Geography Note (Chapters 16) PDF

Course Facilitator: Goitom Sisay (Ph.D)  Contents of the course Chapter 1- Introduction-geography, Location, Shape & Size, & Basic Skills of Map Reading Chapter 2- The Geology of Ethiopia and the Horn Chapter 3- The Topography of Ethiopia and The Horn Chapter 4- Drainage...

Course Facilitator: Goitom Sisay (Ph.D)  Contents of the course Chapter 1- Introduction-geography, Location, Shape & Size, & Basic Skills of Map Reading Chapter 2- The Geology of Ethiopia and the Horn Chapter 3- The Topography of Ethiopia and The Horn Chapter 4- Drainage Systems & Water Resource of Ethiopia & the Horn Chapter 5 - The Climate of Ethiopia and The Horn Chapter 6 - Soils, Natural Vegetation and Wildlife Resources of Ethiopia and The Horn Chapter 7 - Population of Ethiopia and the Horn Chapter 8- Economic Activities In Ethiopia  Meaning of Geography It is difficult to forward a definition acceptable to all geographers at all times due to the dynamic nature of the subject and its scope in its long history. Geography has undergone profound changes in its scope and focus: In ancient times, geography was considered to be the mother of many other sciences, including philosophy and the earth sciences. In the 16th century, geography began to emphasize location, focusing on questions of where, why and what. In the mid 18th century, European geographers, especially Germans, considered the relationship between geography with philosophy. This approach caused geography to focus on the relationship between human and the natural environment.  Meaning of Geography ……. In the 19th century, geographical societies and research groups formed. They enhanced the role of geography as a discipline. In the late 20th century, geography became spatial science. From the ancient Greeks to modern-day geographers, geography has been defined differently. However, the following may be accepted as a working definition. Geography is the scientific study of the Earth that describes and analyses spatio-temporal distribution, variations, interactions and relationships of phenomena ( physical, biological and human) over the surface of the Earth 2. The Scope, Approaches and Themes of Geography Geography is a holistic and interdisciplinary field of study Scope means the range and variety of contents which are included in a subject or field of study. The scope of geography is the interface of the atmosphere, lithosphere, biosphere hydrosphere, and anthroposhpere. The scope is wide and diverse in nature  The Scope of Geography…… Geography can be approached by considering a topical-regional continuum The topical (systematic) –approach takes up particular categories of physical or human phenomena as distributed over the Earth Geography of hunger, The geography of climate, The geography of agriculture, The geography of population The Regional approach- focuses on concerns with the associations within regions of all or some of the elements and their interrelationships The geography of Africa, Asia, or Oceania, etc  Themes of Geography Geography has five basic themes 1. Location- is defined as a particular place or position ( Absolute and relative) 2. Place refers to the physical and human attributes of a location. This theme is associated with toponym (the name of a place), site (the description of the features of the place), and situation (the environmental conditions of the place). Each place in the world has its unique characteristics expressed in terms physical and human elements The concept of “place” aids geographers to compare and contrast two places on Earth.  Themes of Geography …. 3. Human-Environment Interaction It human-environment interaction involves three distinct aspects: Dependency- refers to the ways in which humans are dependent on nature for a living Adaptation- relates to how humans modify themselves, their lifestyles and their behavior to live in a new environment with new challenges Modification-allowed humans to “conquer” the world for their comfortable living and desirable end.  Themes of Geography …. 4. Movement - entails to the translocation of human beings, their goods, and their ideas within different spatial and temporal scale. 5. Region- A region is a geographic area having distinctive characteristics that distinguishes itself from adjacent unit(s) of space It could be a formal region or functional/ nodal.  1.2. Location, Shape and Size of Ethiopia and the Horn The Horn of Africa, a region of eastern Africa, is a narrow tip that protrudes into the northern Indian Ocean, separating it from the Gulf of Aden. It includes Djibouti, Eritrea, Ethiopia, and Somalia, whose cultures have been linked throughout their long history. In terms of size, Ethiopia is the largest of all the Horn of African countries, while Djibouti is the smallest. The Horn contains diverse physical elements like the highlands of the Ethiopian Plateau, the Ogaden desert, and the Eritrean and Somali coasts as well as the human aspects.  1.2.1. Location of Ethiopia The location of a country or a place on a map or a globe is expressed in two different ways. These are astronomical and relative locations 1. Astronomical location, also known as absolute or mathematical location, states location of places using the lines of latitudes and longitudes. Astronomically, Ethiopia is located between 3oN (Moyale) and 15oN (Bademe - the northernmost tip of Tigray) latitudes and 33oE (Akobo) to 48o E (the tip of Ogaden in the east) longitudes.  Location of Ethiopia….. The latitudinal and longitudinal extensions are important in two ways. First, as a result of its latitudinal extension the country experiences tropical climate Secondly due to its longitudinal extension there is a difference of one hour between the most easterly and most westerly points of the country 2. Relative location expresses the location of countries or places with reference to the location of other countries (vicinal), landmasses or water bodies. Relative location of Ethiopia Thus in relative term, Ethiopia is a landlocked country located in; East and South East of Sudan West of Dijbouti Northeast of south sudan West and nortwest of Somalia South and southwest of Eritrea North of Kenya  Relative location of Ethiopia In relation to other features in the world the location of Ethiopia might be expressed in the following way, In the Horn of Africa Southwest of the Arabian Peninsula South of Europe Northwest of the Indian Ocean In the Nile Basin The relative location of Ethiopia has implications for its: Climate Socio-cultural Geopolitics Hydropolitics  1.2.2. Size of Ethiopia Ethiopia with a total area of approximately 1,106,000 square kilometers is the 8th largest country in Africa and 25th in the World. The size of Ethiopia also affects both the natural and human environment of the country. The advantages and disadvantages of the size of Ethiopia are Size of Ethiopia…….  1.2.3. The shape of Ethiopia and its Implication Countries of the World have different kinds of shape that can be divided into five main categories Compact - the distance from the geographic center of the state to any of the boarder does not vary greatly. It is easier for defense and for socio-economic integration Fragmented shape countries: They are divided from their other parts by either water, land or other countries. Elongated (linear) shape countries: are geographically long and relatively narrow like Chile. Perforated shape countries: A country that completely surrounds another country like the Republic of South Africa. 17  Protrude shape countries: Countries that have one portion that is much more elongated than the rest of the country like Myanmar and Eritrea.Fragmented 18  The shape of Ethiopia and its Implication…… There are various ways of measuring shape of countries. These measures are known as the indices of compactness.  These indices measure the deviation of the shape of a country from a circular shape, which is the most compact shape.  Since there is no country with absolutely circular shape, those approximating a circular shape are said to be more compact  There are four most commonly used measures of compactness. These are: 1. Area-Boundary(A/B) ratio: The ratio of area of country to its boundary length.  The higher the A/B ratio, the greater the degree of compactness.  The shape of Ethiopia and its Implication…… 2. Boundary-Circumference(B/C) ratio: The ratio of boundary length of a country to the circumference of a circle having the same area as the country itself. It measures how far the boundary of a country approximates the circumference of a circle of its own size. Therefore, the nearer the ratio to 1 the more compact the country is. 3. Area-Circumference(A/C) ratio. The ratio of the area of the country to the circumference of the smallest inscribing circle. It compares the area of the country with the circumference of a circle that passes touching the extreme points on the boundary of the country  The shape of Ethiopia and its Implication……. The higher the A/C ratio, the greater the degree of compactness. 4. Area-Area (A/A’) ratio: The ratio of the actual area of a country to the smallest possible inscribing circle The area of the inscribing circle is the area of the smallest possible circle whose circumference passes through the extreme points on the boundary. Half-length of the longest distance between two extreme points gives radius of the inscribing circle. The nearer the ratio to 1, the more compact the country is.  The shape of Ethiopia and its Implication…… Ethiopia’s shape compared to some other countries 1.3. Basic Skills of Map Reading A map is a simplified, diminished, plain representation of all or part of the earths surface as viewed from vertically above. Although many disciplines use maps, they have a special significance for Geographers as primary tools for displaying and analyzing spatial distributions, patterns and relations. Importance of maps Provide the basis for making geographical details of regions are powerful tools for making spatial analysis of geographical facts of areas represented.  Importance of maps…… are useful for giving location of geographical features by varied methods of grid reference, place naming etc.... make storage of the geographical data of areas represented. are potentially used to asses’ reliable measurements of the geographical features. The measurements can be of area size, distance etc are used on various disciplines like land use planning, military science, epidemiology, geology, economics, history, archaeology, agriculture etc.  Types of Map Although most maps have similar characteristics, they can differ from one another in many ways 1. Topographical maps (General-Purpose Maps): Topographic maps depict one or more natural and cultural features of an area.  Show limited detailed information They could be small (1:50,000)depending on the size of the area represented.  Types of Map…… 2. Special purpose/statistical maps/thematic maps or topical maps These are maps, which show distribution of different aspects such as temperature, rainfall, settlement, vegetation etc. Soil maps Vegetation maps Climate map Marginal Information on Maps Maps are used to convey information. To read maps effectively, map users need information about the map. Such information is presented in the maps margins and is known as marginal information. Marginal information includes:  Marginal Information on Maps…… a. Title: It is the heading of the given map which tells what the map is all about. b. Key (legend): It is the list of all convectional symbols and signs shown on the map with their interpretation. c. Scale: It is the ratio between the distance on the map and the actual ground distance. This information indicates the extent to which the area that is represented in the map has been reduced Scales enable the map user to interpret the ground measurement like road distance, areal sizes, gradient etc.  Marginal Information on Maps….. It can be expressed as representative fraction, statements/verbal scale, and linear (graphic) scale. d. North arrow: It is indicated with the north direction on a map; used to Shows the north direction on the map. e. Margin: Is the frame of the map. It is important for showing the end of the mapped area. f. Date of compilation: It is a date of map publication. This enables map users to realize whether the map is updated or out- dated.  Marginal Information on Maps….. Basic Principles of Map Reading- map readers need to have ideas about the symbol and also the real World (landscapes) knowledge of directions is an important principle in reading maps locating places using latitudes and longitudes or grid references  left to right,- easting (heading eastward), and northing's (heading in a northward direction).  Chapter Two: The Geology Of Ethiopia And The Horn Geology is an Earth science that studies the evolution of the earth, the materials of which it is made of and the processes acting upon them. Much of Geology is concerned with events that took place in the remote past Geological understanding must, therefore, be obtained by inferences and clues These clues are based on Rocks and landforms- Direct Method Characteristics of seismic waves – Geo-Physics Geochemistry (analysis of the detailed composition of rocks which can give clues as to their origin) Geochronology (methods for finding the ages of rocks, usually from the radioactive elements they contain).  Continental Drift Theory Alfred Wegener proposed the hypothesis of continental drift in 1911 The continental drift hypothesis proposes that the earth’s continents were once assembled to form the super single continent Pangaea. The large super continent was then split into Gondwanaland where Africa is a part and Laurasia; and later into smaller fragments over the last million years. These then drifted apart to form the present arrangement of continents.  Wegener’s Evidence He gathered information from many different sources and used it as evidence for his hypothesis 1. Structural- Fit of the continents: The opposing coastlines of continents often fit together like puzzle pieces  Wegener’s Evidence…… 2. Palaeontological- Distribution of fossils: The distribution of plants and animal fossils on separate continents forms definite linked patterns if the continents are reassembled. fossils are remains of living things that lived long ago. similar fossils have been discovered in matching coastlines on different continents.  Wegener’s Evidence…… 3. Match of mountain belts, rock types: If the continents are reassembled as Pangaea, mountains in West Africa, North America, Greenland, and Western Europe match up. Some mountain ranges on different continents seem to match Ex: ranges in Canada match Norway and Sweden Ex: Appalachian Mtn. match UK mtn  Wegener’s Evidence…… 4. Paleoclimatic- : rocks formed 200 million years ago in India, Australia, South America, and southern Africa all exhibited evidence of continental glaciations. 2.1 The Geologic Processes: Endogenic & Exogenic Forces  Geology studies how Earth's materials, structures, processes and organisms have changed over time. These processes are divided into two major groups 1. The internal processes (endogenic) include volcanic activity and all the tectonic processes (folding, faulting, orogenesis (mountain building), and epeirogenesis (slow rising and sinking of the landmass). These processes result in building of structural and volcanic features like plateaus, rift valleys, Block Mountains, volcanic mountains, etc. 2. The external (exogenic) processes are geomorphic processes. They include weathering, mass transfer, erosion and deposition. They act upon the volcanic and structural landforms by modifying, roughening and lowering them down. The landmass of Ethiopia, as elsewhere, is the result of the combined effect of endogenic and exogenic processes 2.3. The Geological Time Scale and Age Dating Techniques The Earth is believed to have been formed approximately 4.6 billion years ago and the earliest forms of life were thought to have originated approximately 3.5 billion years ago. The geological time scale measures time on a scale involving four main units: An epoch is the smallest unit of time on the scale and encompasses a period of millions of years. Epochs are clumped together into larger units called periods. Periods are combined to make subdivisions called Eras. An eon is the largest period of geological time. Era Period Began (in Million End Major Events (million years ago) Years) Quaternary 1.6 Present Major glaciers in North America and Europe (1.5) Cenozoic Tertiary 70 1.6 Rocky Mountains (65), individual continents take shape. Cretaceous 146 70 Dinosaurs extinct (65), western interior seaway and marine reptiles (144 – 65) Mesozoic Jurassic 208 146 Pangaea (one land mass) begins to break up (200) Triassic 225 208 First mammals and dinosaurs Permian 290 225 Greatest extinction on Earth (245) Pennsylvanian 322 290 First reptiles Paleozoic Mississippian 362 322 Coal-forming forests Devonian 408 362 First land animals and first forests (408) Silurian 439 408 Life invades land Ordovician 510 439 First fish appeared Cambria 600 510 Great diversity of marine invertebrates Proterozoic 2,500 600 Marine fossil invertebrates (600) Precambrian Archean 4,500 2,500 Earliest fossils recorded (3,500), earlies t rock formation (4,000)  Age Dating Techniques There are two techniques of knowing the age of rocks: Relative and absolute age dating. Relative dating is geological evidence to assign comparative ages of fossils. Use the layers of rock formation and sequences of depositions – "What is on top of the older rocks?“ This only works if the area has been undisturbed.  Absolute Dating- Also known as Radiometric techniques. Uses radioactive elements such as uranium (U) and thorium (Th) decay naturally to form different elements or isotopes of the same element. Every radioactive element has its own half-life. Half-life is the time needed for half of a sample of a radioactive element to undergo radioactive decay and form daughter isotopes. Two of the major techniques include: 1. Carbon-14 Technique: Upon the organism’s death, carbon-14 begins to disintegrate at a known rate, and no further replacement of carbon from atmospheric carbon dioxide can take place. Carbon-14 has half-life of 5730 years. 2. Potassium-Argon Technique: (K-Ar) Dating The decay is widely used for dating rocks. Geologists are able to date entire rock samples in this way, because potassium-40 is abundant in micas, feldspars, and hornblendes. Potassium-40 has half-life of 1.3 billion years.  Rate of Decay t0 All atoms are parent isotope or some known ratio of parent to daughter 1 half-life period has elapsed, half of the t1 material has changed to a daughter isotope (6 parent: 6 daughter) 2 half-lives elapsed, half of the parent t2 remaining is transformed into a daughter isotope (3 parent: 9 daughter) 3 half-lives elapsed, half of the parent t3 remaining is transformed into a daughter isotope (1.5 parent: 10.5 daughter) We would see the rock at this point. 2.4. Geological Processes and the Resulting Landforms of Ethiopia and the Horn 2.4.1. The Precambrian Era Geologic Processes (4.5 billion - 600 million years ago) It covers 5/6th of the Earth’s history. Due to its remoteness in time and the absence of well-preserved fossils, our knowledge of the events is limited. The major geologic event of this Era was Orogenesis-that resulted in intense folding Old basement complex (crystalline basement= metamorphic rock= Precambrian era) In addition, the Precambrian era was known for extensive denudation responsible for peneplanation. The penepnained land was covered with younger rock formation later in the Mesozoic and cenozoic eras.  The Precambrian Era Geologic Processes......... These sequences of geological processes and activities have resulting landforms and structures. As such, the Precambrian rocks are overlaid by later rock formations of different ages. Despite the Precambrian rocks are overlaid by sequences of rock formation, they are fond exposed in the following areas: In the northern part: Western lowlands, parts of northern and central Tigray. In the western Part: Gambella, Benishangul-Gumuz (Metekel and Asossa), western Gojjam, western Wellega, Illuababora, and Abay gorge. In the southern Part: Guji, southern Omo, and parts of southern Bale and Borena. In the eastern part: Eastern Hararghe. 2.4.2. The Paleozoic Era Geologic Processes (600million - 225 million years ago) The major geological process of this Era was denudation (erosion). The gigantic mountains that were formed by the Precambrian orogeny were subjected to intense and prolonged denudation. At the end, the once gigantic mountain ranges were reduced to a “peneplained” surface. Because of the limited deposition within Ethiopia, rocks belonging to this Era are rare in the country 2.4.3. The Mesozoic Era Geologic Processes (225-70 million yrs ago) It was an Era of slow sinking and rising (epeirogenesis) of the landmass. This process affected the whole present-day Horn of Africa and Arabian landmass. At the same time the land was tilted eastward and therefore lower in the southeast and higher in the northwest. The three periods of the Mesozoic era experienced epeirogenesis in one form or another.  The Mesozoic Era Geologic Processes........ Triassic period: During this period, land subsidence (sinking) began in the south eastern part of Ethiopia and progressed towards the north western part of the country. Sinking was followed by the sea invasion (transgression) from the Indian Ocean. As a result, the sea invaded the land from the southeast towards the northwest Transgression of the sea resulted in the deposition (sedimentation) of the first sedimentary rock in Ethiopia which is now called Adigrat (lower) sandstone, after its geological naming.  The Mesozoic Era Geologic Processes........ Due to the tilting of the landmass during the transgression and regression of the sea, and due to the direction of the invading and retreating sea, the age and thickness of the Sandstone layers vary in a Southeast - Northwest direction As such, the Adigrat sandstone is older and thicker in the southeast and progressively decreases in age and thickness north-westward  The Mesozoic Era Geologic Processes........ Jurassic period It is manifested by the continued sinking of the land and deepening of the sea in Ethiopia. As a result, sedimentation of another (second type of sedimentary rock) layer took place. This is now called Hintalo limestone. This limestone is composed of remains of dead creatures of the invading sea, sands and gravels.  The Mesozoic Era Geologic Processes........ Cretaceous period During this period great up lifting began. In Ethiopia, great uplifting took place in the north western part. Because of this, the sea which had covered the land surface of Ethiopia was forced to go back (regress). The regression was followed by the deposition of the third layer, called upper sandstone, which is thicker and younger in the Southeast, while in the Northwest it is older and thinner.  The Mesozoic Era Geologic Processes........ The transgressing sea and Mesozoic sediments nearly covered the whole of Ethiopia. Hence, by the end of the Mesozoic era, many parts of Ethiopia were covered by the three layers of Mesozoic marine sediment. Such as Central Tigray, western slopes of Western highlands, and Southeast lowlands. 2.4.4. The Cenozoic Era Geologic Processes (70million years ago - Present) The tectonic and volcanic activities that took place in this Era have an important effect in the making of the present-day landmass of Ethiopia and the Horn of Africa. These five major geologic activities are: A) The continuation of the uplifting of land masses that began at the end of the Mesozoic era resulted in elevated surface mainly in central Ethiopia reaching a maximum height of 2000meters. B) Following this uplifting and fracture, a huge mass of lava known as the Trappean lava series flowed out covering the Mesozoic sediment deposits forming the plateaus of Ethiopia.  Cenozoic era…. C) Major faulting and rifting took place in Central Ethiopia and Ethiopian rift system was formed. It is said to be related with the theory of plate tectonics. According to the theory, the Rift Valley may be lying on the Earth’s crust below which lateral movement of the crust in opposite directions producing tensional forces (in the divergent plate boundaries) that caused parallel fractures or faults on the sides of the up-arched swell. As the tension widened the fractures, the central part of the landmass collapsed to form an extensive structural depression known as the Rift Valley  Cenozoic era…. Reversed tilting and volcanic activity, later (Pleistocene) blocked the connection and isolated the extension of the sea, allowing much of the water to evaporate. As a result, thick saline materials accumulated.  The Formation of the Rift Valley…….. During the same period, the area between the Danakil Depression and the Red Sea was uplifted to form the Afar Block Mountains. The Ethiopian Rift Valley is part of the Great East African Rift system that extends from Palestine-Jordan in the north to Malawi- Mozambique in the south, for a distance of about 7,200 kilometers. Of these, 5,600 kilometers is in Africa, and 1,700 kilometers in Eritrea and Ethiopia. On land, the widest part of the Rift Valley is the Afar Triangle (200- 300 km).  The Formation of the Rift Valley…….. The Red Sea, the Gulf of Aden, and the East African System meet and form the triangular depression of the Afar where the Kobar Sink lies about 125 meters below sea level. The Rift Valley region of Ethiopian is the most unstable part of the country. There are numerous hot springs, fumorales, active volcanoes, geysers, and frequent earthquakes. The formation of the Rift Valley has the following structural (physiographic) effects: It divides the Ethiopian Plateau into two.  The Formation of the Rift Valley…….. It separates the Arabian landmass from African landmass. It causes the formation of the Dead Sea, Red Sea and the Gulf of Aden troughs. It creates basins and fault depressions on which the Rift Valley lakes are formed. Faulting and graben formation are not only limited to the Rift Valley. For example, similar tectonics activities have occurred in the Lake Tana Basin. However, the formation of Lake Tana had been accentuated by volcanic activity so that lava flow in the southeast had dammed part of the rim to deepen the basin  Cenozoic era…. D) The deposition of quaternary volcanic eruption and depositions are often termed as the Aden volcanic series which includes: Numerous and freshly preserved volcanic cones, many of which have explosive craters. Some of these are active Dubi, Erta Ale, Afrera etc. Of these, Erta Ale is the most active volcano in Ethiopia. Volcanic hills and mountains, some of which are semi-dormant (Fantale, Boseti-Gouda near Adama, Aletu north of Lake Ziway, Chebbi north of Lake Hawassa etc.). Extensive lava fields and lava sheets some of which are very recent. Lava ridges. Thermal springs, fumaroles etc.  Cenozoic era…. E. The occurrence of marked climatic variations in the quaternary period resulted in quaternary sediments/recent deposits. During the Quaternary period of the Cenozoic Era, the Earth experienced a marked climatic change, where warmer and dry periods were alternating with cooler and wet periods.. This was the time of the last ‘’Ice Age’’ in the middle and high latitude areas and the time of the ‘‘Pluvial Rains’’ in Africa. The heavy Pluvial Rains eroded the Ethiopian plateau and the eroded materials were deposited in the Rift Valley lakes.  Cenozoic era…. Lake and marshy areas became numerous and deep: Many were enlarged and covered much area and even merged together. Example, Ziway-Langano-Shalla; Hawasa-Shallo; Chamo-Abaya; Lake Abe and the nearby smaller lakes and marsh basins formed huge lakes After the ‘‘Pluvial Rains’’, the Earth’s climate became warmer and drier. Thus, it increased the rate of evaporation that diminished the sizes of the lakes. Areas covered with water and sediments were exposed. Accordingly, there are different types of deposits which are known to us at present.  Quaternary Volcanic Eruptions and Depositions….. These deposits are divided into the following based on the place they occupy, the manner of deposition and depositing agent. Lacustrine deposits: Deposits on former lakebeds and swampy depressions. Fluvial deposits: Deposits on the banks of rivers, flood plains both in plateau, foothills etc. Glacio-fluvial deposits and erosional features: These occurred on high mountains, such as Bale and Kaka Mountains. Aeolian deposits: are windblown deposits. Coastal and marine deposits: Deposits on sea invaded and sea-covered  Quaternary Volcanic Eruptions and Depositions….. The quaternary deposits are mainly found in the Rift Valley (Afar and Lakes Region), Baro lowlands, southern Borena, and parts of north western low lands. Generally, the Cenozoic rocks cover 50% of the land mass of the country. These include Highland Tertiary volcanic (basalts), Tertiary as well as Quaternary volcanic, and sediments of the rift valley. 2.5. Rock and Mineral Resources of Ethiopia  Rock and Mineral Resources of Ethiopia….. The occurrence of metallic minerals in Ethiopia is associated with the Precambrian rocks. The exploitation and search for mineral deposits in Ethiopia has been taking place for the past 2,000 years Such has been the case of gold production and utilization, which has become part of Ethiopia’s history, tradition and folklore (legend). The mining and working of iron for the manufacture of tools, utensils and weapons, and the use of salt and salt-bar all these indicate to a fairly long mining tradition. However, presently mineral production from Ethiopia has been negligible by World standards. 2.5.1. Brief Facts and Current State of Main Minerals in Ethiopia Geological surveys proved that Ethiopia has abundant mineral resources of metals and precious metals, coal, and industrial minerals. Gold has been mined in Ethiopia for quite long time, mainly from Benishangul-Gumuz (Metekel) and Adola.  Operating mines produce gold from primary sources in such localities as Dermi-dama, Sakoro and Lega-dembi. Mechanised alluvial working is confined to the state operated gold field of Adola.  Facts and Current State of Main Minerals in Ethiopia.. Secondary gold deposits are common in the following localities: Adola, Murmur Basin, Makanisa (Guba and Wombera), Kaffa. Shakiso, Awata Basin, Dawa Basin, Ghenale Basin, Ujama Basin,  In Gambella and Illuababora (Akobo River), In Sidama (Wondo), Borena (Negele-Yabelo area) and in Benishangul-Gumuz (Sherkole), West Wellega, Mengi-Tumat-Shangul areas to the Sudanese border, and the drainage of the Didessa and Birbir. Platinum: The Yubdo area in Wellega, is the only active Ethiopian Platinum mine. Platinum occurrences have been reported from Delatti in Wellega, and the valley of Demi-Denissa and Bone Rivers as well as Tullu Mountain area in Sidama. Tantalum: Significant deposit of tantalum and niobium is found in southern Ethiopia. It occurs in Adola area where Kenticha Tantalum mine with resources of more than 17,000 metric tons of world class ore reserve is found. The sedimentary and volcanic rock activities are also resourceful. Extensive lignite deposits in Ethiopia are found in Nedjo (Wellega), and in small amounts in Chilga (Gonder) are found in the sedimentary formations laid in between Trapean lava.  However, important Lignite, one of the lowest ranked coal, is known to occur in many localities such as in the Beressa Valley and Ankober (North Shewa), Sululta (nearAddis Ababa), Muger Valley (West Shewa), Aletu valley (near Nedjo), Kariso and Selmi Valleys (Debrelibanos), Zega wodem gorge (near Fiche), Didessa Valley (southwest of Nekemte), Kindo and Challe Valley (Omo confluence), Adola,Wuchalle (north of Dessie), Chukga area (on Gonder-Metema road), Dessie area (near Borkena River). These areas are promise to be a good prospect to meet some of the local industrial and domestic needs. Gemstones Gemstones, including amethyst, aquamarine, emerald, garnet, opal, peridot, sapphire, and tourmaline occur in many parts of Ethiopia, mainly in Amhara and Oromia Regional States. Quality Opal was first discovered by local people in Wadla and Dalanta woredas, North Wello in Amhara Regional State. Potash The potash reserve in the Danakil (Dallol Depression) of the Afar region is believed to be significant. Gypsum and Anhydrite A limited amount of gypsum is produced for domestic consumption in Ethiopia, mainly for the cement industry, but very large deposits are known to occur in sedimentary formations of the Red Sea coastal area, Danakil Depression, Ogaden, Shewa, Gojjam, Tigray, and Hararghe. Total reserves are probably enormous because the thickness of the gypsum deposits is many hundreds of meters and the formation are known to extend laterally for hundreds of kilometers. Clay Ethiopia is endowed with industrial clay material. Alluvial clay deposits for bricks and tile, pottery and pipe industry occur in Adola, Abay gorge, and the Rift Valley lakes region. Ceramic clay for the production of glasses, plates, bricks is found at Ambo and Adola. Tabor ceramic industry in Hawassa gets most of its raw materials from local sources. Marble Crystalline limestone is widespread in the basement rocks of Ethiopia. Marble has been quarried in such localities as west of Mekelle and south of Adwa in Tigray. In the east in Galetti, Soka, Ramis, Rochelle, Kumi and other valleys of Chercher Mountain in West Hararghe. In the northwestern also in areas built of Precambrian schist in Gonder, and the Dabus River and other neighboring river basins in Benishangul- Gumuz and Gojjam.  Construction stones Basalt, granite, limestone and sandstone are important building stones. For the surfacing of roads and compaction, basalt, scoria and other volcanic rocks are extensively used. Mesozoic limestone is an important raw material for cement and chalk production. The earlier cement works at Dire Dawa and the recent ones at Muger Valley, Abay gorge (Dejen), Tigray (Messebo) are using similar raw materials from these rock formations.  2.5.2. Mineral Potential Sites of Ethiopia According to the Ethiopian geological survey, the geologic formations that host most mineral potentials of Ethiopia includes three major greenstone belts and other formations. These are: 1. The Western and South-western-greenstone belt They contain various minerals: primary gold occurrences (Dul,Tulu- Kape,Oda-Godere, Akobo,Baruda,Bekuji-Motish and Kalaj);Yubdo Platinum, Base metals of AzaliAkendeyu, Abetselo and Kata;Fakushu Molybdenite and the iron deposits of Bikilal, Chago, Gordana and Korre, Benshagul-Gumuz- Marble, Akobo and Asosa placer gold deposits and etc. 2. The Southern greenstone belt: It is known as the Adola belt, which comprises the primary gold deposits and occurrences of Lega-dembi, Sakaro, Wellena, Kumudu, Megado-Serdo, Dawa Digati, Moyale and Ababa River; the columbo- tantalite of kenticha and Meleka, and the Adola nickel deposit and other industrial minerals. 3. The Northern greenstone belt(Tigray): This belt comprises of the primary gold occurrences of Terakemti, Adi- Zeresenay, and Nirague. The base metals of Terer, Tsehafiemba and other parts of Tigray, Placer gold occurrences of Tigray.  Chapter 3: The Topography Of Ethiopia And The Horn 3.1 General Characteristics of the Ethiopian Physiography Flat-topped plateaus, high and rugged mountains, deep river gorges and vast plains. Altitude ranges from 125 meters below sea level (Kobar Sink) to the highest mountain in Ethiopia, Mount Ras Dashen (4,620 m.a.s.l), which is the fourth highest mountain in Africa. The Roof of East Africa because more than 50% of the Ethiopian landmass is above 1,000 meters of elevation; and above 1,500 meters makes 44% of the country. For most parts of the country are sources of many rivers and streams, the country is described as the “Water Tower of East Africa”.  Ethiopian Physiography… Taking the 1,000 meters contour line for the highland-lowland demarcation, one observes the following contrasting features between the Ethiopian highlands and lowlands: Characteristics of Ethiopian highlands: - Moderate and high amount of rainfall (>600 mm per year). - Lower mean annual temperature (2,000 m.a.s.l).  Ethiopian Physiography…… The remaining 44% of the Ethiopian lowlands are characterized by: - Fewer amounts of rainfall and higher temperature. - High prevalence of tropical diseases. - Lower population densities. - Nomadic and semi-nomadic economic life. - Vast plain lands favorable for irrigation agriculture along the lower river basins. 3.2. The Physiographic Divisions of Ethiopia The three major physiographic units are: 1.The Western highlands and lowlands 2. The South-Eastern (Eastern) highlands and lowlands 3.The Rift Valley Below is the map showing the topography of Ethiopia  3.2.1. The Western Highlands and Lowlands Includes all the area west of the Rift Valley. Makes up about 44% of the area of the country. Encompass nearly the whole western half of Ethiopia. Further subdivided into four groups of highlands (76.3%) and four groups of lowlands (23.7%). 1. The Western Highlands a. The Tigray Plateau Extends from the Tekeze gorge in the south to central Eritrean highlands. Separated from the Eritrean plateau by the Mereb River. Lies to the southeast of the upper course of the Mereb/Gash River and to the northeast of Tekeze River Gorge. Constitutes about 13% of the area of the region. Most of the land being in between 1,000 and 2,000 meters above sea level.  The Western Highlands and Lowlands…. Denudation has created residual features of granite hills, rugged topography, and Ambas. High mountains in this plateau include Mount Tsibet (3988 m.a.s.l), Mount Ambalage (3291 m.a.s.l), and Mount Assimba (3248 m.a.s.l). The famous monastery at Debre-Damo is also located in this plateau region.  The Western Highlands and Lowlands…. b. North Central Massifs Is the largest in the western highlands ( near to 53%). Much of its northern and southern limit follows the Abay and Tekeze gorges. In its central part, it accommodates the Lake Tana basin surrounded by plains of Fogera and Dembia in the north & an upland plain in its south. 58% of the region is at an altitude of > 2,000 meters making it, next to the Shewan Plateau. Consists of the Gonder, Wello and Gojjam Massifs. Among the known mountain peaks, the most popular ones include  The Western Highlands and Lowlands….. - Mount Ras Dashen (4,620 m.a.s.l) - Mount Weynobar/Ancua (4462 m.a.s.l) - Mount Kidis Yared (4453 m.a.s.l) and Mount Bwahit (4437 m.a.s.l) in the Simen Mountain System - Mount Guna (4,231m.a.s.l) in the Debre Tabour Mountain System - Abune Yoseph (4,260 m.a.s.l) in the Lasta highlands of Wello and - Mount Birhan (4,154 m.a.s.l) in the Choke Mountain System in Gojjam are also part of Simen Mountain System. Yeju-Wadla Delanta land bridge (ridge) has been significant in history. It served as a route of penetration by the Turks, Portuguese, and Italians etc. North Central Massifs…..  The Western Highlands and Lowlands….. c. The Shewa Plateau/central highlands Is bounded by the Rift Valley in the east & southeast, by the Abay gorge in its northern & western limit, & the Omo gorge in the south and west. Occupies a central geographical position in Ethiopia. Is the smallest of the Western highlands (constituting 11 %). Has the largest proportion of elevated ground (3/4th of its area-above 2000 m). Is drained, outward in all directions by the tributaries of Abay, Omo, and Awash. The tributaries of Abay-Guder, Muger, Jema etc. have cut deep gorges and steep sided river valleys.  The Western Highlands and Lowlands….. They have created several tablelands and isolated plateau units in the north. The tributaries of Omo and Awash have dissected the other sides of the plateau. Has relatively extensive flat-topped uplands, giving it the appearance of a true plateau. Highest mountain in the Shewan plateau include Mount Abuye-Meda (4,000 m.a.s.l) in Northern Shewa, Mount Guraghe (3,731 m.a.s.l) in the south.  The Western Highlands and Lowlands….. d. The South-western Highlands Consists of the highlands of Wellega, Illuababora, Jimma, Kaffa, Gamo and Gofa. Is separated from the adjacent highlands by the Abay and Omo river valleys. Extends from the Abay gorge in the north to the Kenya border and Chew Bahir in the south. Accounts for 22.7% of the area of the region & is the second largest in the Western highlands. About 70% of its area is lies within 1,000-2,000 meters altitude. Is the wettest in Ethiopia & is drained by Dabus, Deddessa (tributaries of Abay), Baro, Akobo and the Ghibe/Omo rivers.  The Western Highlands and Lowlands….. Accommodates the most numerous and diverse ethnic linguistic groups in Ethiopia. Guge Mountain (4,200 masl) is the highest peak in this region.  The Western Highlands and Lowlands….. 2. The Western Lowlands Are the western foothills & border plains that extend from Western Tigray in the north to southern Gamo-Gofa in the South. Make 23.7% of the area of the physiographic region. The general elevation ranges between 500 and 1000 masl. Is further subdivided into four by the protruding ridges. These are Tekeze lowland, Abay-Dinder lowland, Baro lowland, and Ghibe lowland from north to south.  The Western Highlands and Lowlands….. With the exception of the Baro lowland, the region is generally characterized by arid or semi-arid conditions. Pastoral or semi-pastoral economic activities dominate the area. The Ghibe/Omo lowland structurally also belongs to the Rift Valley. In the Western lowlands, there are small but important towns (in terms of agriculture, history, or are simply border towns and frontier ports);These are Humera, Metema, Omedla, Kurmuk, Gambella etc. 3.2.2. The Southeastern Highlands and Lowlands Is the second largest in terms of area & accounts for 37% of the area of Ethiopia. The highlands make up 46% of the physiographic division while the rest is lowland..  The Southeastern Highlands and Lowlands….. 1. The Southeastern Highlands A.The Arsi-Bale-Sidama Highlands Found to the east of the Lakes Region. Make up 28.5% of the area of the region and 62% of the south - Eastern Highlands. The well-known mountains in Arsi Highlands are Mount Kaka (4,180 m.a.s.l), Mount Bada (4,139 m.a.s.l) and Mount Chilalo (4,036 m.a.s.l). The Bale highlands are separated from the Arsi highlands by the head and main stream of Wabishebelle. The Afro-Alpine summit of Senetti plateau is found in Bale high lands. The highest mountain peaks in Bale Mts. are Tulu-Demtu (4,377 m.a.s.l) and Mount Batu (4,307 m.a.s.l). The Arsi-Bale Highlands are important grains producing areas with still high potential.  The Southeastern Highlands and Lowlands….. The Sidama Highlands are separated from the Bale Highlands by the Ghenale river valley. The prominent feature in Sidama highland is the Jemjem plateau, an important coffee growing area.  The Southeastern Highlands and Lowlands….. Rivers Wabishebelle and Ghenale along with their tributaries have dissected this physiographic region. Specially, Weyb River, tributary of Ghenale, has cut an underground passage (Sof Omar cave, i.e. a spectacular cavern) through the Mesozoic Limestone rocks. The cave is found near Bale Mountains.  The Southeastern Highlands and Lowlands….. B. The Hararghe Plateau Is a north-easterly extension of the south-eastern highlands & extends from the Chercher highland in the south-west to Jigjiga in the east. Makes up 38% of the South Eastern highland and 17.4% of the whole physiographic region. Has the smallest proportion of upper highland (>2,000 meters) & is a low lying and elongated region. The left-bank tributaries of Wabishebelle drain it. The highest mountain here is Mount Gara-Muleta (3,381 m.a.s.l). 2. The Southeastern Lowlands Are located in the southeastern part of the country and are the most extensive lowlands in Ethiopia: Make up 54% of the area of the physiographic region & around one-fifth of the country. Is divided into Wabishebelle plain (60%) & the Ghenale Plain (40%). Include the plains of Ogaden, Elkere, and Borena. Because of the harsh climatic conditions, these lowlands are little used and support very small population. Are sparsely inhabited by pastoral and semi-pastoral communities. Its economic potential includes animal husbandry, irrigation, agriculture and perhaps exploitation of petroleum & natural gas.  3.2.3. The Rift Valley Is a tectonically formed structural depression & is bounded by two major more or less parallel escarpments. Has separated the Ethiopian Highlands and Lowlands into two. It extends from the Afar triangle in the north to Chew Bahir It covers 18% of the area of Ethiopia. It is elongated and funnel shaped, with a NE-SW orientation. It opens out in the Afar Triangle, where it is the widest, and narrows down to the south. The floor of the Rift Valley is made up of interconnected troughs, grabens and depressions.  The Rift Valley….. Volcanic rocks, fluvial and lacustrine deposits cover the floor. In many places, numerous volcanic domes, hills and cinder cones rise from the floor. Altitude in the floor ranges from 125 m.b.s.l at Dallol Depression, to as high as 2,000 m.a.s.l in the Lakes region. Because of its altitudinal variation and positional differences, the climate also varies from warm, hot and dry to cool and moderately moist conditions. Similarly, the social and economic life reflects this pattern. Sparsely inhabited by pastoralists where as in others parts people practice some rain-fed agriculture. It is Further subdivided into three physiographic sub-regions: The Afar Triangle, the Main Ethiopian Rift, and the Chew Bahir Rift. The Rift Valley…..  The Rift Valley….. i. The Afar Triangle Is the largest and widest part of the Rift Valley & makes up 54% of the Rift Valley area. Is bounded by the high western and eastern escarpments in the west and east respectively, and by the Afar and Aisha Horst in the northeast. The area is generally of low altitude (300-700 meters). Is triangular-shape lowland. Its elevation drops from 1,000 meters in the SW to below sea level in the North (Danakil depression) and in the east, where the shores of Lake Asal, fluctuating at around 125 meters below sea level The lowest point in this region represents the lowest sub-aerial point of the African continent.  The Rift Valley….. The depression, which hosts one of the most hostile environments on Earth (Max. temp. > 50 Degree Celsius, at Dallol). The area is characterized by faulted depressions, volcanic hills, active volcanoes, volcanic ridges, lava fields and low lava platforms. Lakes (Abe, Asale, and Afrera) occupy some of these basins. A prominent feature in this region is the Denakil Depression (Kobar Sink). Separated from the Red Sea by a 200 meters high land barrier, much of it lies below sea level. A larger part of this is covered by thick and extensive salt plain. Lake Asale and Lake Afrera occupy the lowest parts of this sunken depression. The Afar Triangle is generally hot and dry. The only respite one gets in the Southern part is from the waters of the Awash River. The economic importance of this region includes salt extraction, irrigation along the Awash River & electric potential from geothermal energy.  The Rift Valley….. ii. The Main Ethiopian Rift/Central Rift Refers to the narrow belt of the Rift Valley that extends from Awash River in the north to Lake Chamo in the south. With the exception of the Arbaminch area, the bounding escarpments are generally low. Is the narrowest & the highest & has an average width of 50-80 kms and general elevation of 1,000-2,000 m.a.s.l. The floor in many places is dotted by cinder cones & volcanic mountains. The big ones include Mount Fentale, Boseti-guda (near Adama), Aletu (north of Lake Ziway) & Chebi (north of Lake Hawasa).  The Rift Valley….. Contains numerous lakes formed on tectonic sags and fault depressions. Is generally milder and watery. Here rain-fed agriculture is practiced. Other resource bases include the recreational value of the lakes, the agricultural importance of some streams and lakes, and the geothermal energy potential.  The Rift Valley….. iii. The Chew Bahir Rift Is the smallest and the southern-most part of the Rift Valley. Gneissic highlands of Konso and the surrounding highlands separate it from the Main Ethiopian Rift to the north. The characteristic feature of this region is the broad and shallow depression, which is a marshy area covered by tall grass, into which the Segen and Woito streams empty. 3.3. The Impacts of Relief on Biophysical and Socioeconomic Conditions The highly dissected character of the landscape over much of the country influence the various socioeconomic aspects of Ethiopia as presented hereunder. 1.Agricultural practices Relief influences farm size and shape in that in an area of rugged terrain the farmlands are small in size and fragmented and tend to be irregular in shape.  Choice of farming techniques and farm implements are highly influenced by relief. Relief influences crop production. The practice of animal husbandry is also influenced by relief. 2.Settlement pattern Rugged & difficult terrain hinders the development of settlement and its expansion. Highlands of Ethiopia are densely settled.  The Impacts of Relief ….. The highlands of Ethiopia are characterized by sedentary life & permanent settlements while lowlands that are inhabited by pastoralists have temporary settlements. 3. Transportation and communication The highly dissected nature of the landscape is a barrier to the development of transportation. The difficult terrain makes infrastructure development & maintenance costly. TV and radio communications are also highly influenced by relief. The rugged topography rendered rivers less navigable due to the waterfalls, deep gorges and steep cliffs. 4. Hydroelectric power potential The great difference in altitude coupled with high rainfall created suitable conditions for a very high potential for the production of HEP in Ethiopia.  The Impacts of Relief ….. 5. Socio-cultural feeling The rugged terrain as a result of excessive surface dissection resulted in isolation of communities that led to the occurrence of cultural diversity. People who live in the highlands - degegnas (mountaineers) and those who live in the lowlands-kollegnas (lowlanders). 6. Impacts on climate The climate of Ethiopia is a result of the tropical position & the great altitudinal variation. Highlands with higher amount of RF & lower rate of Evaporation tend to be moisture surplus compared to the moisture deficit lowlands. 7. Impacts on soil Steep mountain slopes have shallow and little developed soils. 8. Impacts on natural vegetation Relief through its effect on climate and hydrology affect the type of natural vegetation grown in an area.  Chapter Four DRAINAGE SYSTEMS AND WATER RESOURCE OF ETHIOPIA AND THE HORN  4.1 Introduction About 71% of the earth’s total surface is covered by water bodies majorly occupied by seas and oceans. Of the earth’s total water surface, nearly 97.5% is alkaline accumulated in seas and oceans. Alkaline water is water that is slightly basic. It contains basic minerals such as calcium, magnesium, or bicarbonate. These compounds bind to hydrogen ions in solution, making the water more basic. The remaining 2.5% is fresh water, of which nearly 68.7% is deposited in glaciers, 30.1% in ground water, 0.8% in permafrost and 0.4% in surface waters. Water in lakes, rivers, atmosphere, soils and wetlands are considered as surface waters. Surface and ground waters are by far the most abundant and easily available fresh waters. However, fresh water is distributed unevenly throughout the world following varied latitudinal locations, climatic and topographic setups.  Introduction …….. As you have discussed in the third chapter, the topographic setup of Ethiopia is characterized by complex blend of massive highlands, rugged terrain, and low plains. The diverse topographical setup, relatively higher rainfall and its nearness to equator made the country to have larger volume of ground and surface water. Around 0.7% of the total land mass of Ethiopia is covered by water bodies. Although it requires further detailed investigation, the country’s surface water potential as studied in different integrated river basin master plans is estimated to be 124.4 billion cubic meters (BCM). Consequently, many call Ethiopia, the water tower of “Eastern Africa”.  4.2. Major Drainage System of Ethiopia The flow of water through well-defined channel is known as drainage. A drainage system is made up of a principal river and its tributaries (the rivers that flow into it). A river system begins at a place called the source or headwater and ends at a point called mouth. Therefore, a drainage system is branched network of stream channels together with the adjacent land slopes they drain. The drainage pattern of an area is the outcome of the geological processes, nature and structure of rocks, topography, slope, amount and the periodicity of the flow. A drainage basin is the topographic region from which a river and its tributaries collect both the surface runoff and subsurface flow. It is bounded by and separated from other river basins by a water divide or topographic divide.  Major Drainage System of Ethiopia…… The general patterns of major river basins in Ethiopia are determined by topographical structures which can be clarified as: a. The topography of the outward sloping of the Western and South eastern plateaus b. The structural formation of the Rift Valley with its in-ward-sloping escarpments resulting mainly in an inland drainage system. c. Faults and joints that structurally influence part of the courses of many rivers. The Major Drainage Systems Following the complex physiographic setup and geological makeup, Ethiopia possesses three broadly classified drainage systems namely Western, Southeastern and Rift Valley Drainage Systems. Western and the Southeastern drainage systems are separated by the Rift Valley system.  4.2.1. The Western Drainage Systems The Western Drainage Systems are the largest of all drainage systems draining 40 percent of the total area of the country and carry 60 percent of the annual water flow. Most of the catchment area coextends with the westward sloping part of the western highlands and western lowlands. This drainage system comprises four major river basins namely the Tekeze, Abay, Baro-Akobo, Ghibe (Omo). Unlike other river basins in the system, the Ghibe (Omo) flows southward. The Abay, Tekeze and Baro flow westward ultimately joining the Nile  The Western Drainage Systems….. The largest river both in volumetric discharge and coverage in the western drainage systems is the Abay. Abay river basin covers an area of 199,812 km2, covering parts of Amhara, Oromia and Benishangul-Gumuz regional states. Together with its tributaries, most of which are left-bank tributaries; it carries 65 percent of the annual water flow of the region. Abay which rises from Lake Tana (some sources indicate its origin from Sekela, Choke mountain) flows about 1,450 kilometers and joins the White Nile in Khartoum, Sudan to form the Nile River.  The Western Drainage Systems….. More than 60 streams drain the Abay within elevation ranging between 500 - 4261 meters above sea level. The largest of these is Ghilgel Abay (Little Abay). Abay flows eastward, turns 180 degree to make a large bend and after cutting an impressive and deep gorge emerges out in the west. Similarly, the Tekeze and its tributaries, carrying 12 percent of the annual water flow of the region drains 82,350 Km2 of land surface within elevation ranging between 536-4517 meters above sea level. Erosion in the basin resulted in large tablelands, plateau blocks and isolated mountain groups.  The Western Drainage Systems….. The basin has two main tributaries (Angereb and Goang) which rises in the central highlands of Ethiopia. Tekeze River is termed Atbara in Sudan, which is a tributary of the Nile. The total mean annual flow from the basin is estimated to be 8.2 billion metric cubes (BMC). The Baro-Akobo and Ghibe / Omo rivers drain the wettest highlands in the south and southwestern Ethiopia. They carry 17 percent and 6 percent of the annual water flow respectively. The Ghibe/ Omo river basin drains an area of 79,000 km2 with an estimated mean annual flow of 16.6 BMC.  The Western Drainage Systems….. In the lower course, the Baro River flows across an extensive marshy land. Baro/Akobo river basin has an area of 75,912 km2, covering parts of the Benishangul-Gumuz, Gambella, Oromia, and SNNPR. The total mean annual flow from the river basin is estimated to be 23.6 BMC. The Baro together with Akobo forms the Sobat River in South Sudan. The Ghibe / Omo River finally empties in to the Chew-Bahir at the mouth of Lake Turkana (an elongated Rift Valley lake) thereby forming an inland drainage. 4.2.2. The Southeastern Drainage Systems Nearly the entire physiographic region of southeastern part of Ethiopia is drained by the southeastern drainage systems.  The Southeastern Drainage Systems ….. The basin which is mainly drained by Wabishebelle and Ghenale, slopes south-eastwards across large water deficient plains. Major highlands of this basin include plateaus of Arsi, Bale, Sidama and Harerghe. Wabshebelle and Ghenale rivers cross the border into Somalia, carrying 25 percent of the annual water flow of Ethiopia. Ghenale River basin has an area of 171,042 km2, covering parts of Oromia, SNNPR, and Somali regions. Ghenale, which has fewer tributaries but carries more water than Wabishebelle, reaches the Indian Ocean.  The Southeastern Drainage Systems ….. The Ghenale basin flows estimated to be 5.8 BMC within elevation ranging between 171-4385 meters above sea level. In Somalia it is named the Juba River. Wabishebelle with a total catchment area of 202,697 km2, is the largest river in terms catchment area. It drains parts of Oromia, Harari and the Somali regions. It is the longest river in Ethiopia. Its tributaries are mainly left bank and, most of them, are intermittent.  The Southeastern Drainage Systems ….. Despite its size, the Wabishebelle fails to reach the Indian Ocean where at the end of its journey it flows parallel to the coast before its water disappears in the sands, just near the Juba River.  4.2.3. The Rift Valley Drainage System The Rift Valley drainage system is an area of small amount of rainfall, high evaporation and small catchment area. The size of the drainage area is restricted by the outward sloping highlands, which starts right from the edge of the escarpment. The Rift Valley drainage system is therefore left with the slopes of the escarpment and the Rift Valley floor itself as the catchment area. The only major river basin is that of the Awash. Awash river basin has a catchment area of 114,123 km2 and has an average annual discharge of 4.9 billion cubic meters.  The Rift Valley Drainage System …… The Awash River originates from Shewan plateau in Central highlands of Ethiopia, and flows 1250 kms. It covers parts of the Amhara, Oromia, Afar, Somali, Dire Dawa, and Addis Ababa City Administration. Awash is the most utilized river in the country. In the Rift Valley drainage systems, there is no one general flow direction, as the streams flow in all directions. Following the rift valley orientation the Awash flows in a NE direction. It finally ends in a maze of small lakes and marshy area; the largest of which is Lake Abe on the Ethio-Djibouti border.  The Rift Valley Drainage System …… The Afar drainage sub-basin has practically no stream flow. It is an area of little rain, very high temperature and very high evaporation. Lake Afrera and Asale are the only main surface waters in the basin which are not the result of any meaningful surface flow. Their formation is related to tectonic activities. The Southern part of the Rift Valley sub-basin is characterized by a number of lakes and small streams. It is also described as lakes region. The lakes occupy fault depression  The Rift Valley Drainage System …… There are small streams that drain down from the nearby mountain slopes which supply water to the lakes. For example, Meki and Katar Rivers flow into Ziway Bilate into Abaya and Segen into Chew Bahir. Likewise, some of these lakes are interconnected. Lakes Ziway and Langano drain into Lake Abijiata through the small streams of Bulbula and Horocolo respectively.  4.3. Water Resources: Rivers, Lakes and Sub-Surface Water 4.3.1. The Ethiopian Rivers Unlike many other African countries, Ethiopia is endowed with many rivers. Majority of the rivers originate from highland areas and cross the Ethiopian boundary. Altogether, Ethiopian rivers form 12 major watersheds separating the Mediterranean Sea from the Indian Ocean drainage systems.  Table 4.1: Data on major Ethiopian rivers River Catchment Annual Terminus/ Major tributaries Area(km2) Volume Mouth BMC Abay 199,812 54.5 Mediterranean Dabus, Dedessa, Fincha, Guder, Muger, Jema, Beshilo Wabishebelle 202,697 3.4 Coast of Indian Ocean Ramis Erer, Daketa Fafan Genale Dawa 171,042 6 Indian-Ocean Dawa, Weyb, Welmel, Mena Awash 114,123 4.9 Inland-within Ethiopia Akaki, Kesem, Borkena, Mile Tekeze 87,733 8.2 Mediterranean Goang, Angereb Gibe (Omo) 79,000 16.6 Lake Turkana Gojeb Baro Akobo 75,912 23.23 Mediterranean Akobo  The Ethiopian Rivers …… Owing to the highland nature of the Ethiopian landmass, surface ruggedness, the outward inclination of the highlands, and the climatic conditions, Ethiopian rivers have the following characteristics. Almost all major rivers originate from the highlands elevating more than 1500 meters above sea level, Majority of Ethiopian rivers are trans-boundary, Due to the marked seasonality of rainfall, Ethiopian rivers are characterized by extreme seasonal fluctuation. In the wet season, runoff is higher while during the dry seasons they became mere trickles of water/even dry up,  The Ethiopian Rivers …… Due to surface ruggedness they have rapids and waterfalls along their course, They have cuts, steep-sided river valleys and deep gorges along their courses, Rivers in Ethiopia flow on steep slopes having steep profiles. Some of the rivers serve as boundaries, both international and domestic administrative units.  4.3.2. The Ethiopian Lakes Relatively Ethiopia is rich in lakes. Almost all Ethiopian lakes are result of tectonic process that took place during Quaternary period of Cenozoic era. Except few Ethiopian lakes, majority of lakes are located within the Rift Valley System. The lakes in the drainage are mainly formed on faulted depressions and are clustered along the system forming linear pattern. Lake Tana, the largest lake in Ethiopia occupies a shallow depression in the highlands.  The Ethiopian Lakes …… The Tana depression is believed to be formed following slower sinking and reservoir by lava flow between Gojjam and Gonder massifs. Ethiopia is also gifted with crater lakes. These include the lakes at and around Bishoftu, Wonchi (near Ambo), Hayk (near Dessie) and the Crater Lake on top of Mount Zikwala. Lake Ashenge (Tigray) is formed on a tectonic basin. Other types of lakes in Ethiopia are man-made such as Lakes Koka, Fincha and Melka Wakena, and many other lakes dammed following hydroelectric power generation projects.  The Ethiopian Lakes …… Cluster of lakes are lined up within main Ethiopian rift. Lake Abaya is the largest of all the lakes in the system. The southern tip of the Rift Valley forms the marshy land called the Chew Bahir which is drained by Segan and Woito. Shala and Ziway are the deepest and the shallowest lakes in the central Ethiopian Rift  Table 4.2: Area and depth of some of Ethiopian Lakes Lake Area (km2) Max. Lake Area Max. Depth(m) Depth(m) (km2) Tana 3600 9 Abijata 205 14 Abaya 1162 13.1 Awassa 129 10 Chamo 551 13 Ashenge 20 25 Ziway 442 8.95 Hayk 5 23 Shala 409 266 Beseka 48.5 11 Koka 205 9  4.3.3. Subsurface (Ground) Water Resource of Ethiopia As compared to surface water resources, Ethiopia has lower ground water potential. However, there exists higher total exploitable groundwater potential. Climatic and geophysical conditions determine the availability of groundwater resource. Based on existing scanty knowledge, the groundwater potential of Ethiopia is estimated to be 2.6 - 6.5 BMC. However, this estimate is now considered underestimated. Considering various separate studies, Ethiopian potential of groundwater is believed to range between 12-30 BMC.  4.4. Water Resources Potentials and Development in Ethiopia The enormous water resource potential of Ethiopia is underutilized due to so many factors. However, there are plenteous of opportunities that can transform the resource into our collective social and economic needs. The followings are some of potential development uses of water resource of Ethiopia. a) Hydro-electric Potential Ethiopian rivers have a very high potential for generating electricity. The exploitable potential of hydroelectric power is estimated at about 45000 megawatts.  Water Resources Potentials and Development in Ethiopia……. The first hydroelectric power generation plant was installed on Akaki River (Aba Samuel) in 1932. Currently many hydroelectric power dams are operating and many others are under construction to realize Ethiopia's ambitious energy goals. Grand Ethiopian Renaissance Dam (GERD) is the country's largest dam under construction aiming to generate 6400 megawatts. Gilgel Gibe III hydropower project has gone operational generating 1870 megawatts.  Water Resources Potentials and Development in Ethiopia ……. Currently Ethiopia is administering 14 hydroelectric power plants constructed on Lake Aba Samuel, Koka, Tis Abay, Awash, Melka Wakena, Sor, Fincha, Gibe/Omo, Tana Beles and Tekeze, generating close to 4000 megawatts of energy. Besides the domestic use of generated electricity, the country is exporting electricity to the neighboring countries. The major problem related to the use of Ethiopian rivers for the generation of hydroelectric power is the seasonal flow fluctuations and impact of climate change and variability. The severe erosion from the highlands and sedimentation in the reservoirs is also a critical problem for hydroelectric power generation.  Water Resources Potentials and Development in Ethiopia ……. b) Irrigation and Transportation The terrain in Ethiopia is so rugged that it limits the uses of Ethiopian rivers both for irrigation and transportation. In the highlands, steep slopes, rapids, waterfalls, narrow and deep valleys and gorges are important obstacles. But on the lowlands, their demand for irrigation is high. Regardless of existing physiographic setups, Ethiopia's potential of irrigation is estimated to be 5.3 million hectares. The Baro-Akobo and Genale Dawa river systems have large irrigation potential compared to other basins.  Water Resources Potentials and Development in Ethiopia……. Despite the untapped irrigation practice, more than 60% of the area under irrigation so far is located in Rift Valley Drainage System. Except few, majority of hydro-electric reservoirs are multi-purpose and are expected to contribute for irrigation. Majority of Ethiopian rivers are not suitable for transportation. The Baro at its lower course is the only navigable river. Comparatively, Ethiopian lakes are much suitable for transportation than rivers. Lake Tana and Abaya are relatively the most used for transportation  Water Resources Potentials and Development in Ethiopia ……. c) Fishing and Recreation The majority of Ethiopian lakes are rich in fish. Currently the annual production of fish is estimated to be 31.5 thousand tons. The exploitable potential is however, by far greater than the current production. Exploitable fish potential in lakes varies. Currently Lake Tana leads the potential by estimated 8,000-10,000 tons per year. Fish production from Lake Chamo is estimated at 4,500 tons per year.  Water Resources Potentials and Development in Ethiopia ……. However, more than 60% of fish supplies are coming from Ethiopian main Rift Valley lakes. However, some of the lakes are currently threatened by sedimentation, invasive species, over exploitation and expansion of investments around lakes. There are a variety of fish, birds and other aquatic life forms in the lakes, some of which are only endemic to Ethiopia, with immense scientific purposes. This and the scenic beauty of the lakes, the hot springs, the spectacular river gorges & the most impressive waterfalls make Ethiopian rivers & lakes important recreational & tourist attractions. Chapter 5 : The Climate Of Ethiopia & the Horn Of Africa 5.1 Introduction  Ethiopia, is characterized by a wide variety of altitudinal ranges and diverse climatic conditions.  In addition, because of its closeness to the equator and the Indian Ocean, the country is subjected to large temporal and spatial variations in elements of weather and climate.  The climate of Ethiopia is, therefore, mainly controlled by the seasonal migration of the Intertropical Convergence Zone (ITCZ) and associated atmospheric circulations as well as by its complex topography.  The convergence of Northeast Trade winds forms the ITCZ, which is a low-pressure zone.  Climate of Ethiopia…. ITCZ, circles the Earth generally near the equator where the trade winds of the Northern and Southern Hemispheres come together. It is characterized by convective activity which generates often vigorous thunderstorms over large areas. It is most active over continental land masses by day and relatively less active over the oceans. Climate of Ethiopia…. Climate of Ethiopia….  Climate of Ethiopia…. Weather is the instantaneous or current state of the atmosphere composing temperature, atmospheric pressure, humidity, wind speed and direction, cloudiness and precipitation. Climate refers the state of the atmosphere over long periods, decades and more. It is the composite of daily weather conditions recorded for long periods of time. 5.2. Elements and Controls of Weather and Climate All weather conditions may be traced to the effect of the Sun on the Earth. Most changes in weather involve large scale horizontal motion of air which is called wind. Here are lists of major elements and controls of weather and climate. Table 5.1 Elements and controls of weather and climate Elements Controls 1. Temperature 1Latitude/angle of the Sun 2. Precipitation and 2Land and water distribution humidity 3. Winds and air pressure 3Winds and air pressure 4Altitude and mountain barriers 5Ocean currents  Climate of Ethiopia…. 5.2.1. Controls of Weather and Climate  What do you think is the source of summer rainfall in Ethiopia?  Have you ever noticed varying lengths of days and nights by seasons? What do you think is the reason behind?  The climate of any particular location on earth is determined by a combination of many interacting factors.  These include latitude, elevation, nearby water, ocean currents, topography, vegetation, and prevailing winds.  Moreover, the global climate system and any changes that occur within it also influence local climate.  Climate of Ethiopia…. a. Latitude Latitude is the distance of a location from the equator measured in degrees. The sun shines directly on equator for more hours during the year than anywhere else. As you move further away from the equator towards the poles, less solar insolation is received during the year and the temperature become colder. Ethiopia’s latitudinal location has bearings on its temperature. Latitudinal location of Ethiopia and the Horn resulted in: oHigh average temperatures, oHigh daily and small annual ranges of temperature, oNo significant variation in length of day and night between summer and winter.  Climate of Ethiopia…. b. Inclination of the Earth's Axis  The Earth's rotation axis makes an angle of about 66½° with the plane of its orbit around the sun, or about 23½° from the perpendicular to the ecliptic plane.  This inclination determines the location of the Tropics of Cancer, Capricorn, and the Arctic and Antarctic Circles.  As the earth revolves around the sun, this inclination produces a change in the directness of the sun's rays; which in turn causes the directness of the sun and differences in length of day and seasons. Climate of Ethiopia….  Climate of Ethiopia…. Equinoxes and Solstices An equinox is the instant of time when the sun strikes the plane of the Earth's equator. During this passage the length of day and night are equal. Moreover, revolution of the earth along its orbit, the inclination of its axis from the plane of that orbit, and the constant position (parallelism) of the axis causes seasonal changes in the daylight and darkness periods. Equinox appears twice a year. There are two types of equinoxes:  Climate of Ethiopia…. 1. The Vernal (Spring) equinox It is the day when the point of verticality of sun’s rays crosses the equator northwards. It experiences in Northern Hemisphere when the sun is exactly above the equator. During this period, the length of day and night are equal. It marks the beginning of spring season. March 21 marks the offset of the this equinox. 2. The Autumn equinox It appears when the sun crosses equator giving approximately equal length between day and night. It appears to happen when the visible sun moves south across the celestial equator on 23rd of September. It marks the beginning of Autumn season.  Climate of Ethiopia…. Solstice It is an event when the overhead sun appears to cross northern or southern points relative to the celestial equator resulting in unequal length of days and nights in the hemispheres. The Summer Solstice On June 21st, the northern hemisphere has maximum tilt towards the sun experiencing longest daylight of the year. It is the astronomical first day of summer in the Northern Hemisphere. The sun is at its highest position in the noonday sky, directly above 23½0 in the Tropic of Cancer. The Winter Solstice On 22nd of December, the day when the maximum southward inclination is attained in the Southern Hemisphere..  Climate of Ethiopia…. In this event the sun travels shortest length causing longest night and shortest daylight. In the Northern Hemisphere, it occurs when the sun is directly over the Tropic of Capricorn, which is located at 23½° south of the equator. c. Altitude Altitude is the height of location above the sea level. Under normal conditions there is a general decrease in temperature with increasing elevation. The average rate at which temperature changes per unit of altitudinal change is known as lapse rate. The lapse rate is limited to the lower layer of the atmosphere ( troposphere)  Climate of Ethiopia…. The normal lapse rate is 6.5°C per kilometer rise in altitude. There are 3 types of lapse rates: i. Dry adiabatic laps rate An adiabatic lapse rate is the rate at which the temperature of an air parcel changes in response to the expansion or compression process associated with a change in altitude. When air rises, it expands because there is less weight of air upon it. Thus, if a mass of dry air at sea level rises to an altitude of about 5486.22meters, the pressure upon it is reduced by nearly half and consequently its volume is doubled.  Climate of Ethiopia…. If the upward movement of air does not produce condensation, then the energy expanded by expansion will cause the temperature of the mass to fall at the constant dry adiabatic lapse rate. The rate of heating or cooling is about 10°C for every 1000m of change in elevation. This rate applies only to unsaturated air, and thus it is called the dry adiabatic laps rate. The rate at which rising or sinking saturated air changes its temperature is less than the dry adiabatic rate. Prolonged cooling of air invariably produces condensation, thereby liberating latent heat.  Climate of Ethiopia…. Therefore, rising and saturated or precipitating air cools at a slower rate than air that is unsaturated. This process is called wet adiabatic temperature change. The rate of cooling of wet air is approximately 50c per 1000meters ascend. iii. Environmental lapse rate/Atmospheric lapse late This refers to the actual, observed change of temperature with altitude. The fact that air temperature is normally highest at low elevations next to the earth and decreases with altitude.  Climate of Ethiopia…. This decrease in temperature upward from the earth's surface normally prevails throughout the lower atmosphere called troposphere because of temperature inversions. The rate of change is 6.50C/1000meters. 5.3.1 Spatio-temporal Distribution of Temperature The spatial distribution of temperature in Ethiopia is primarily determined by altitude and latitude. The location of Ethiopia at close proximity to equator, a zone of maximum insolation, resulted for every part of the country to experience overhead sun twice a year. However, in Ethiopia, as it is a highland country, tropical temperature conditions have no full spatial coverage. They are limited to the lowlands in the peripheries.  Climate of Ethiopia…. Away from the peripheries the land begins to rise gradually and considerably, culminating in peaks in various parts of the country. Thus temperature, as it is affected by altitude, decreases towards the interior highlands. Mean annual temperature varies from over 300C in the tropical lowlands to less than 100C at very high altitudes. The Bale Mountains are among highlands where lowest mean annual temperatures are recorded. The highest mean maximum temperature in the country is recorded in the Afar Depression. Moreover, lowlands of NW, W and SE Ethiopian experiences mean maximum temperatures of > 300C  Climate of Ethiopia…. Environmental influences have their own traditional expressions in Ethiopia and there are local terms denoting temperature zones as shown in the table below. Altitude Mean annual Temp Description Local (meter) (0C) Equivalent 3,300 and 10 or less Cool Wurch above 2,300 - 3,300 10 – 15 Cool Dega Temperate 1,500 - 2,300 15 – 20 Temperate Woina Dega 500 - 1,500 20 – 25 Warm Kola Temperate below 500 25 and above Hot Bereha  Climate of Ethiopia…. The temporal distribution of Ethiopian temperature is characterized by extremes. The major controls determining its distributions are latitude and cloud cover. However, some parts of the country enjoy a temperate climate. In the tropics, the daily range of temperature is higher and the annual range is small, whereas the reverse is true in the temperate latitudes. In Ethiopia, as in all places in the tropics, the air is frost free and changes in solar angles are small making intense solar radiation. Ethiopia’s daily temperatures are more extreme than its annual averages.  Climate of Ethiopia…. Daily maximum temperature varies from a high of more than 37oC over the lowlands in northeast and southeast to a low of about 10-15oC over the northwestern and southwestern highlands. The variation in the amount of solar radiation received daily is small throughout the year. In Ethiopia and elsewhere in the Horn of Africa, temperature shows seasonal variations. For example, months from March to June in Ethiopia have records of highest temperatures. Conversely, low temperatures are recorded from November to February. It is not easy to observe distinct variation in temperature between seasons as the sun is always high in the tropics. However, there is a slight temperature increase in summer.  Climate of Ethiopia…. Southern part of Ethiopia receives highest records of temperature in autumn and spring following the relative shift of the sun; whereas in the northern part of the country, summer season is characterized by higher temperature. It has to be noted that certain seasons should have special considerations. For instance, unlike other parts of Ethiopia, the southern and southwestern highlands experience reduced temperature. This is because the temperature and the amount of energy reaching the surface is directly related with the directness of the sun.  Climate of Ethiopia…. 5.3.2 Spatio-temporal Distribution of Rainfall  Rainfall in Ethiopia is influenced by the position of Intertropical Convergence Zone (ITCZ).  The convergence of Northeast Trade winds and the Equatorial westerlies forms the ITCZ, which is a low-pressure zone.  The inter-annual oscillation of the surface position of the ITCZ causes a variation in the Wind flow patterns over Ethiopia and the Horn.  Following the position of the overhead sun, the ITCZ shifts north and south of the equator.  As the shift takes place, equatorial westerlies from the south and southwest invade most parts of Ethiopia bringing moist winds. The ITCZ shifts towards south of the equator (Tropic of Capricorn) in January.  Climate of Ethiopia…. During this period, the Northeast Trade Winds carrying non- moisture-laden dominates the region. Afar and parts of Eritrean coastal areas experience rainfall in this period. Following the directness of the sun in March and September around the equator, the ITCZ shifts towards equator. During this time, the central highlands, southeastern highlands and lowlands receives rainfall as the south easterlies bring moist winds. Seasonal or Temporal Variability's of rainfall in Ethiopia The seasonal and annual rainfall variations observed in Ethiopia are the results of the macro-scale pressure systems and monsoon flows which are related to the changes in the pressure system.  Climate of Ethiopia…. 1. Summer season (June, July, August) oFrom mid-June to mid-September, majority of Ethiopian regions, except lowlands in Afar and Southeast, receive rainfall during the summer season as the sun overheads north of the equator. High pressure cells develop on the Atlantic and Indian Oceans around the tropic of Capricorn although the Atlantic contributes a lot; the Indian Ocean is also source of rainfall. During this season, Ethiopia and the Horn of Africa come under the influence of the Equatorial westerlies (Guinea monsoon) and Easterlies. Hence, these winds are responsible for the rain in this season.  Climate of Ethiopia…. 2. Autumn Season (September, October and November) In autumn the ITCZ shifts towards the equator weakening the equatorial westerlies. During this season, the south easterlies from Indian Ocean showers the lowlands in southeastern part of Ethiopia. 3. Winter season (December, January and February) The overhead sun is far south of equator. Northeasterly winds originating from the landmass of Asia dominantly prevail Ethiopian landmass. However, it has no significant coverage compared to other seasons. The northeasterly winds crossing the Red Sea carry very little moisture and supplies rain only to the Afar lowlands and the Red Sea coastal areas.  Climate of Ethiopia…. 4. Spring Season (March, April and May) The noonday sun is shining directly on the equator while shifting north from south. The shift of the ITCZ, results in longer days and more direct solar radiation providing warmer weather for the northern world. In this season, the effect of the northeast trade wind is very much reduced. Conversely, the Southeasterlies from the Indian Ocean provide rain to the highlands of Somalia, and to the central and southeastern lowlands and highlands of Ethiopia.  Climate of Ethiopia…. Rainfall Regions of Ethiopia Based on rainfall distribution, both in space and time, four rainfall regions can be identified in Ethiopia and the Horn. These are: i. Summer rainfall region This region comprises almost all parts of the country, except the southeastern and northeastern lowlands. The region experiences most of its rain during summer (kiremt), while some places also receive spring (Belg) rain. The region is divided in to dry and wet summer rainfall regions. Hence, the wet corresponds to the area having rainfall of 1,000mm or more. The High altitudes and the windward side experience such rainfall amount.  Climate of Ethiopia…. ii. All year-round rainfall region It has many rainy days than any part of the country. It is a rainfall region in the southwestern part of the country. The wetness of this region is particularly due to the prepotency of moist air currents of equatorial westerlies called the Guinea Monsoons. Both duration and amount of rainfall decreases as we move from southwest to north and eastwards. The average rainfall in the region varies from 1,400 to over 2,200mm/year.  Climate of Ethiopia…. iii. Autumn and Spring rainfall regions The region comprises areas receiving rain following the influence of southeasterly winds. South eastern lowlands of Ethiopia receive rain during autumn and spring seasons when both the north easterlies and equatorial westerlies are weak. About 60% of the rain is in autumn and 40% in spring. The average rainfall varies from less than 500 to 1,000mm. iv. Winter rainfall region This rainfall region receives rain from the northeasterly winds. During the winter season, the Red sea escarpments and some parts of the Afar region receive their main rain.  Climate of Ethiopia…. 5.4 Agro-ecological Zones of Ethiopia Due to diversified altitude and climatic conditions, Ethiopia possesses five agro-climatic zones (Bereha, Kolla, Woina Dega, Dega and Wurch) traditionally been defined in terms of temperature.  Climate of Ethiopia…. The Wurch Zone The Wurch-zone is an area having altitude higher than 3,200meters above sea level and mean annual temperature of less than 10oC. Mountains having typically fitting characteristics of this zone include mountain systems of Ras Dashen, Guna, Megezez in North Shoa, Batu, Choke, Abune Yoseph etc. Dega Zone This is a zone of highlands having relatively higher temperature and lower altitude compared to the wurch Zones. In Ethiopia, the Dega-zone is long inhabited and has dense human settlement due to reliable rainfall for agriculture and absence of vector-borne diseases such as malaria.  Climate of Ethiopia…. Weyna Dega Zone It lies between 1500-2,300meters above sea level This zone has warmer temperature and moderate rainfall highly suitable for majority of crops grown in Ethiopia. Hence, the zone includes most of the agricultural land. It is the second largest zone covering more than 26% of the landmass of Ethiopia. The Weyna Dega zone has also two growing seasons. Kolla Zone Peripheries in south, southeast, west and northeastern part are mainly in this category making the first largest zone covering more than 52% It is the climate of the hot lowlands with an altitudinal range of 500 to 1500meters above sea level. Average annual temperature ranges between 20oC and 30oC.  Climate of Ethiopia…. Although mean annual rainfall is erratic, it can be as high as 1500mm in the wet western lowlands of Gambella. Bereha Zone It is the hot arid climate of the desert lowlands largely confined to lowland areas with altitude of lower than 500meters. Around Danakil depression, the elevation goes below the sea level. Its average annual rainfall is less than 200mm, and average annual temperature is over 27.5oC. Djibouti, majority of Somalia, and coastal areas of Eritrea are categorized under Kolla and Bereha zones. Figure 5.2. Traditional Agro Ecological Zones of Ethiopia.  Climate of Ethiopia…. 5.5. Climate Change: Causes, Consequences and Response Mechanisms  Climate change refers to a change in the state of the climate that can be identified by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. 5.5.1. Current Trends of Climate in Ethiopia  Besides spatial & temporal variations in different parts of the country, Ethiopian climate experiences extremes such as drought, flood etc.  Ethiopia ranked 5th out of 184 countries in terms of its risk of drought.  Climate of Ethiopia…. In Ethiopia, 12 extreme drought events were recorded b/n 1900 - 2010. Among the 12, seven of the drought events occurred since 1980. The majority of these resulted in famines. The severe drought of 2015-2016 was exacerbated by the strongest El Nino that caused successive harvest failures and widespread livestock deaths in some regions. Trends in Temperature Variability In Ethiopia the mean annual temperature has shown 0.2°C to 0.28°C rise per decade over the last 40-50 years.  Climate of Ethiopia…. A rise in average temperature of about 1.3°C has been observed between 1960 and 2006. Higher rise in temperature was noted in drier