G9 U2 Climate of Ethiopia PDF

2. CLIMATE OF ETHIOPIA Introduction Climate is an important control over agricultural activities, and the materials thedistribution of flora and fauna and available for...

2. CLIMATE OF ETHIOPIA Introduction Climate is an important control over agricultural activities, and the materials thedistribution of flora and fauna and available for shelter and clothing. in consequence largely determines the Unit Outcomes By the end of this unit, you will be able to: recognize the meaning and concepts of weather and climate; identify elements of climate; distinguish elements of climate from its controls; compare and contrast the spatial and temporal variations of climate; and identify factors affecting climate of Ethiopia. 37  Grade 9 | Geography MAIN CONTENTS 2.1 MEANING OF WEATHER AND CLIMATE 2.2 ELEMENTS OF WEATHER AND CLIMATE 2.3 CONTROLS OF WEATHER AND CLIMATE IN ETHIOPIA 2.4 CLIMATIC REGIONS AND SEASONAL VARIATIONS IN ETHIOPIA 2.5 MEASUREMENTS OF WEATHER AND CLIMATE Unit Summary Review Exercise 2.1 MEANING OF WEATHER AND CLIMATE At the end of this section, you will be able to: recognize the meaning and concepts of weather and climate; define weather and climate; and describe the difference between weather and climate. KEY TERMS մ Climate մ Weather What do you know about the concepts of weather and climate? Do you see any change in the weather day in and day out? The word “weather” and “climate” are closely related but have quite different meaning. Weather refers to the condition of the atmosphere in terms of temperature, rainfall, pressure, wind, moisture, cloud cover, humidity etc. observed in a certain place over a short period of time. It is a phenomenon which varies very much from hour to hour, even from day to day. While climate is a pattern of weather condition experienced in an area over a long period of time. It considers the trends, fluctuation and vibration that may occur in departure from the average conditions in time and space. A large area can experience only one type of climate. 38  UNIT TWO CLIMATE OF ETHIOPIA Answer the following question. 1. Write a minimum of three major differences between weather and climate. 2.2 ELEMENTS OF WEATHER AND CLIMATE At the end of this section, you will be able to: identify elements of weather and climate; define the elements of weather and climate; and differentiate the elements of weather and climate from their controls. KEY TERMS Activity 2.1 մ Air pressure մ Precipitation մ Cloud cover մ Temperature մ Humidity մ Wind What are elements of weather and climate? What is the significance of knowing the climatic condition of a place? Both weather and climate are composed of the following elements. Þ Precipitation - is any liquid or frozen water that forms in the atmosphere and falls back to the Earth in form of rain, sleet, hail, and snow. Þ Temperature - is the degree of measurement of hotness or coldness of an object. Þ Humidity - is the concentration of water vapor present in the air Þ Air pressure - is the force exerted on a surface by the air above it as gravity pulls it to Earth. 39  Grade 9 | Geography Þ Wind - Wind is the movement of air, caused by the uneven heating of the Earth by the sun and the Earth’s own rotation. Þ Sunshine- is a direct sunlight to which a given area is exposed. Þ Cloud- is any visible mass of water droplets or ice crystals suspended in the atmosphere. The distribution of these elements over the surface of the earth is uneven in terms of magnitude and time. This spatial and temporal distribution of climatic elements is governed by the climate control factors described in the sections below. Activity 2.2 Answer the following question. 1. List the most important elements of weather and climate in Ethiopia. 2.3 CONTROLS OF WEATHER AND CLIMATE IN ETHIOPIA At the end of this section, you will be able to: distinguish elements of climate from its controls.  KEY TERMS մ Altitude մ Mountain barriers մ Distance from the sea մ Ocean currents մ Latitude There are varieties of climate in Ethiopia. The spatial and temporal distribution of the climatic elements in Ethiopia is determined by various physical factors which are generally known as controls of weather and climate. The most important are: 40 UNIT TWO CLIMATE OF ETHIOPIA a) Latitude b) Altitude c) Mountain Barriers d) Revolution of the earth and the inclination of the earth’s axis e) Distance from the sea f) Ocean Current a) Latitude Latitude, as a climate control, is the angular location of a place or point with reference to the direct rays of the sun. When we speak of the latitudinal impact on the climate of Ethiopia, we are considering angle of the sun ray in country. This is because the rays of the sun fall vertical on the equator and slanting in the temperate and polar regions. Ethiopia’s location within the tropical zone results in; Þ high temperatures during most of the year, Þ high daily (diurnal) ranges of temperature, Þ relatively small annual ranges of temperature, and Þ little difference between summer and winter in the ratios of daylight to night. b) Altitude Do you have information about the altitude of the place where you are living? Is it a highland or lowland? Is the temperature mild or hot or cold? Altitude is the main factor that determines the spatial distribution of temperature in Ethiopia. Different places that exist on the same plane or angle of the rays of the sun might be expected to experience equal temperatures. However, due to the impact of altitude, they do not. For example, three Ethiopian cities, Bako, Addis Ababa, and Awash all lie on the 9oN latitude, and therefore they might be expected to receive equal magnitudes of direct rays from the sun and therefore equal temperatures. However, their altitudes vary, and therefore their temperatures vary, as shown in Table 2.1. 41  Grade 9 | Geography Table 2.1. The Role of Altitude in Modifying Temperatures Towns Latitude Altitude Average annual temperature Addis Ababa 9oN 2,200 m.a.m.s.l. 16oC Bako (West Shewa) 9oN 1,800 m.a.m.s.l. 17oC Awash 9oN 916 m.a.m.s.l. 25oC The table illustrates the effect of altitude on temperature, confirming the fact that temperature decreases as altitude ascends from the lowlands towards the interior highlands. c) Mountain Barriers Mountain barriers can affect climate in that they exert influence on the spatial distribution of rainfall. Places located on the leeward side of mountains (also called rain shadow) receive little rain. The side of the mountain facing the wind laden with moisture is called the windward side mountain. Leeward side is named the other side of the mountain that does not face the laden moisture. Figure 2.1. Effects of Mountain Barriers d)Revolution of the Earth and the Inclination of the Earth’s Axis The axis of the earth inclines 23½o to the normal of the elliptic. As the earth revolves around the sun, this inclination produces a change in the angle of the sun’s rays, thereby affecting the length of time that the sun shines on the earth every other day. Changes in the length of the day and angle (directness) of the sun’s rays cause seasons. These different seasons result in the temporal variation of temperature in a year in Ethiopia. 42  UNIT TWO CLIMATE OF ETHIOPIA e) Distance from the Sea Don’t you expect that water bodies or lakes (at local levels) have a moderating effect on the climate of vicinal or adjacent land areas? Water bodies and landmasses have different levels of heat absorption. Land masses absorb and release heat energy more quickly than water bodies do. Distance from the sea affects the Horn’s climate only in coastal areas that are adjacent to the Red Sea and the northwestern Indian Ocean. Towards the interior, the role of distance from the sea in climate control is insignificant. f) Ocean Current Warm and cold ocean currents can affect the climate of coastal regions, but only when local winds blow in from the sea. Warm currents heat the air over the ocean and bring higher temperatures over land. Cold currents can lower air temperatures and can bring colder temperatures over land. In Ethiopia the role of ocean current in climate control is inconsequential. NOTE Among the above mentioned controls of climate, the climate of Ethi-opia is dominantly controlled by altitude and latitude. Activity 2.3 Answer the following questions 1. Explain how Ethiopia’s latitudinal location affects the distribution of climate. 2. Why is altitude known as the strongest of all the controls of climate in Ethiopia? 3. Why every place in Ethiopia experiences the overhead sun twice in a year? 43  REGIONS AND SEASONAL Grade 9 | Geography 2.4 CLIMATIC VARIATION IN ETHIOPIA At the end of this section, you will be able to: identify agro-climatic zones of Ethiopia; and compare and contrast the spatial and temporal variations of climate in Ethiopia. KEY TERMS մ Agro-climatic zones մ Kolla մ Alpine or Afro-Alpine մ Subtropical մ Bereha մ Woina Dega մ Dega մ Wurch/Kur մ Inter-Tropical Convergence Zone 2.4.1 Agro-climatic Zones of Ethiopia In Ethiopia, the impact made by altitude has resulted in the formation of five agro- climatic zones. These zones have traditionally been defined in terms of temperature (see Table 2.2). Table 2.2. Agro-climatic Zones Altitude in Traditional agro- Global equivalence Mean annual meters ecological name temperature in C o 3,300 and above Wurch/Kur Alpine or Afro-Alpine 30 44  UNIT TWO CLIMATE OF ETHIOPIA a)Wurch-Zone Areas Do you know that the term wurch has resemblance to temperature severity? The Wurch-zone areas have the highest altitudes and lowest temperatures. Frequently they have temperatures of less than 10oC. These areas exist in the very high mountains of South Gondar, Wollo, Shewa, Arsi and Bale. Example: Þ Mt. Ras Dashen in Semine Gondar Þ Mt. Guna in South Gondar Þ Mt. Megezez in North Shewa Þ Mt. Batu in Bale, etc. b) "Dega-Zone Areas What crops are grown in Dega areas? The Dega-zone areas are highland areas with lower altitudes and higher temperatures than Wurch-zone areas. Historically, Dega-zone agro-climatic areas were the home of concentrated human settlement. They were chosen because of the features below: Þ Secure location (from which people could defend themselves from threats) Þ Reliable rainfall Þ Absence of tropical diseases such as malaria, etc. Due to this high concentration of human population, the Dega zone has been intensively cultivated and has a high rate of soil erosion, overgrazing and deforestation. Some of the humid areas of this zone support two growing periods per year under rain-fed agriculture. Example: Þ Dinsho in Bale Þ Hulla in Sidama Þ Chillallo in Arsi Þ Debresina in North Shewa C) Woina-Dega-Zone Areas What is your understanding why the term Woina Dega comes after Dega? Does the term mean milder Dega? The Woina-Dega-zone areas contain most of Ethiopia’s agricultural land. They are the country’s main areas producing: Þ Surplus grain Þ Inset and its derivatives 45  Grade 9 | Geography In the Woina-Dega zone, as in the Dega zone, there can be two growing seasons when rainfall reliability is high. d) Kolla Zone Areas What are the dominant crops grown in Kolla areas? Kolla is a (warm-to-hot semi-arid climate). Kolla is the climate of the hot lowlands with an altitudinal range of 500 to 1500 m a.s.l. Average annual temperatures are between 20oC and 30oC. Although mean annual rainfall ranges between 410 mm and 820 mm, it can be as high as 1600 mm in the wet western lowlands of Gambella. Rainfall is highly variable from year to year. Example: Western lowlands. e) Bereha-Zone Areas Can we grow crops in Bereha zone areas? Bereha is the hot arid climate. Bereha is the climate of the desert lowlands that are found below 500 m above mean sea level where the average annual rainfall is less than 400 mm, and average annual temperature is over 30oC. Bereha is usually characterized by strong wind, high temperature, low relative humidity, and little cloud cover. Evapotranspiration is always in excess of rainfall in some places. Example: Danakil depression in Afar lowlands. 2.4.2 Seasonal Variation in Ethiopia A season is a period of the year characterized by a particular set of weather conditions resulting from the inclination of the earth’s axis and the revolution of the earth around the sun. The same cycle of season is repeated year after year. 2.4.2.1 Seasonal Variation of Temperature in Ethiopia Can you identify the temperature differences in Ethiopia between the months of April/May and those of October/November? How do these differences occur? In Ethiopia, temperatures vary from season to season. For example, in most parts of Ethiopia, high temperatures are recorded from March to June. Conversely, low temperatures are recorded from November to February. These variations are primarily due to: Þ the tilting of the earth at 23½º to the normal elliptic, and Þ the distance of the overhead sun and its apparent north-south movement across the equator as the earth revolves around the sun. 46  UNIT TWO CLIMATE OF ETHIOPIA During the winter season of the northern hemisphere, Ethiopia experiences the “Bega” season. During this season, day have clear skies. Thus, the incoming solar rays are intense. As a result temperature increases in day time and abruptly decreases at night because of clear sky. This, therefore, results in high diurnal range of temperature. Þ The mean maximum temperatures are experienced over the western, north eastern and south eastern lowlands while the lowest temperatures are over the Semein and Arsi-Bale mountains. Þ The highest temperature i.e. over 45oC is recorded in the Danakil Depression - the hottest place of Ethiopia. 2.4.2.2 Seasonal Variation of Rainfall in Ethiopia Do you distinguish the two concepts spatial and temporal? Which of the two terms is very much explanatory in the distribution of rainfall in time series? Rainfall, like temperature is a major element of climate. Ethiopia experiences marked spatial and temporal variations of rainfall. A. Spatial Variation of Rainfall in Ethiopia The spatial variation is the result of strength and nature of prevailing weather systems following the oscillation of the Inter Tropical Convergence Zone (ITCZ). NOTE As described earlier, Ethiopia’s weather systems also result from the apparent movement of the overhead sun, prevailing winds and the presence of barrier that checks the moisture arrival into the area Inter-Tropical Convergence Zone (ITCZ) It is a low atmospheric pressure zone formed by the convergence of northeasterly and southeasterly trade winds. It shifts north and south of the equator following the position of the overhead sun. In June, its position is at the Tropic of Cancer. During this time, Ethiopia comesunder the influence of the Equatorial Westerlies and Easterlies. As they originate from water 47  Grade 9 | Geography bodies, these winds bring moisture to the highlands, but decrease their magnitude and length of rainy periods northwards. In December, its position shifts to the Tropic of Capricorn leaving the region for the prevalence of the Northeast Trade winds that are non-moisture-laden as they originate from the continental landmass. During this time only lowland areas in Afar region close to the coast receive some amount of rain given that these winds pick up little moisture as they blow passing over the Red Sea. In most of Ethiopia, it becomes dry season. In March and September, the position of the ITCZ is around the equator. Hence,the Equatorial Easterlies provide rain to the Southeastern lowlands, Central and highlands of Ethiopia. B. Temporal Variation of Rainfall in Ethiopia Ethiopia’s rainfall is characterized by seasonal variation. There are two main rainy seasons: Kiremt (summer) that extends from June to August and Belg (spring) that covers the time from March to May. These two rainy seasons contribute more than 90% of the country’s rain supply. There are two other rainy seasons namely the Meher (autumn) rains and the Bega (winter) rains. Compared to the two main rainy seasons, the duration, volume, and aerial coverage of Meher (autumn) rains that takes place from September to November are less. The Bega (winter) is generally the dry season that takes place from December to February. It supplies small amount of rain only to the Afar lowlands. 2.4.3 Rainfall Regions of Ethiopia Based on rainfall distribution, both in space and time, five types of rainfall regions can be identified in Ethiopia. These are: a) Year-round rainfall region (wet in most months) b) Summer rainfall region c) Autumn-and-spring rainfall region d) Winter rainfall region e) Merged spring, summer, and autumn rainfall region Each region is discussed in turn as follows 48  UNIT TWO CLIMATE OF ETHIOPIA a. Year-round Rainfall Region (wet in most months) In Ethiopia, the area of year-round rainfall includes the southwestern plateau comprising the highlands of Wollega, Kafa, Illubabor and Gamo and Goffa. The reason for the high rainfall and an exceptionally long wet season is due to the dominance of the equatorial Westerlies wind system. They pick up moisture from the Atlantic Ocean. This region can be represented by the following stations: Gore, Mizan, Metu, Bonga, Gambella, etc. The region has more rainy days than any other part of the country. The average rainfall varies from 1400 mm to 2200 mm. The year-round rainfall region is represented by the letter B on Figure 2.2. b. Summer Rainfall Region The summer rainfall region is the largest in the country. This region consists of the Northwest Highlands and Western Lowlands, and can be represented by the following stations. Debre Markos, Fitche, Gondar, Bahir Dar, etc. Its moisture-bearing winds are the Equatorial Westerlies and Easterlies. The summer rainfall region is represented by the letter A in Figure 2.2. c. Autumn-and-Spring Rainfall Region The autumn-and-spring rainfall region covers the southeastern highlands and associated southeastern lowlands. They can be represented by the following stations: Gode, Moyalle, Jigjiga, Yabello The region’s moisture-bearing winds are the Equatorial Easterlies. They pick up moisture from the Indian Ocean, and they blow over the autumn and spring rainfall region when the Northeasterlies and Equatorial Westerlies are weak. The region’s average rainfall varies from less than 500 to 1000 mm. The autumn-and-spring rainfall region is represented by E in Figure 2.2. 49  Grade 9 | Geography NOTE In Ethiopia, highland rainfall is more dependable than lowland rainfall. However, highland dependability decreases from the southwestern highlands in all directions. In short, rainfall variability (deviation from the expected amount and time) decreases from areas of heavy rains to areas of low rainfall. d. Winter Rainfall Region The winter rainfall region consists of the eastern escarpment of the western highlands, the middle Rift Valley section and the Afar subdivision. The winter rainfall region can be represented by the Assaita station (Afar Region). The region’s moisture-bearing winds are, for the most part, the North Easterlies. The air mass is continental (dry) and has only a short sea trajectory (that is the Red Sea). It is represented by letter D in Figure 2.2. The region’s total annual moisture is very low and of short duration. e. Merged Spring, Summer, and Autumn Rainfall Region The merged spring, summer and autumn rainfall region is the smallest in the country. It consists mainly of the western foothills of the Southeastern Highlands. The region’s total annual rainfall varies from 1500 mm to 1000 mm. It covers a corridor that stretches from the Sidama Highlands to the Hararge Plateau. The merged spring, summer, and autumn rainfall region is represented by the letter C in Figure 2.2. It can be represened by the following stations namely, Assaita, Awash, and etc. 50  UNIT TWO CLIMATE OF ETHIOPIA Figure 2.2. Rainfall Regions of Ethiopia Activity 2.4 Answer the following questions 1. What do we mean by spatial and temporal in the context of Geography? 2. Identify your own agro-climatic zone by referring to your area’s altitude. You might be able to obtain the meters above sea level value of your altitude from your area’s kebele offices or from those of other agencies in your area. Your teacher may help you as you try to get that information so that you can use it to identify your agro-climatic zone. 3. Identify all the characteristics of your agro-climatic zone. 4. Identify the factors that are responsible for the spatial and temporal variation of temperature and rainfall in Ethiopia 5. State the dominant wind systems over Ethiopia during the “Bega” and “kiremt” seasons. 6. Identify your locality, based on its rainfall seasons. In which seasons do you experience rain? 7. What moisture-bearing winds prevail over your area? 8. What is the attractive factor for the moisture coming as rain to your locality? 51  Grade 9 | Geography 2.5 MEASUREMENTS OF WEATHER AND At the end of this section, you will be able to: measure the temperature variation from the thermometer; read the amount of rainfall receipt from a rainguage; measure air pressure with a barometer; and detect wind direction with the help of a wind vane. CLIMATE KEY TERMS մ Anemometer մ Thermometer մ Barometer մ Wind vane մ Rain gauges A. Measuring and Recording Air Temperature Temperature is a very important element of climate and weather. The instrument for measuring temperature is the thermometer, which is a narrow glass tube filled with mercury or alcohol. It works on the principle that mercury expands when heated and contracts when cooled. On thermometers,- temperatures are marked in one of two ways. In °F. (Fahrenheit) the freezing-point is 32°F. and the boiling- point is 212°F. For most scientific purposes the Centigrade °C. scale is preferred. Its freezing-point is 0°C. and its boiling-point is 100°C. These two scales are interconvertible. Look at the following formula:  100 5 180 9 C=(F-32)* =(F-32)* F=(C* )+32=(C* )+32 180 9 100 5 52  UNIT TWO CLIMATE OF ETHIOPIA Focus Mean daily temperature: it is calculated by adding the maximum and minimum temperature of the day and dividing the sum by 2. Daily (diurnal) range of temperature: it is the difference between the daily maximum and daily minimum temperature. Mean monthly temperature: is determined by adding together the daily averages and the dividing the number of days in a month. Mean annual temperature: it is calculated by adding the mean monthly temperatures and dividing the sum by 12. Annual range of temperature: it is the difference between the temperatures of the hottest and coldest months. b. Measuring and Recording Rainfall Rainfall is measured using a rain gauge. The rain gauge is usually anchored in the ground with the top of the gauge around 30cm above the ground surface to ensure that rain splash does not affect the results. The depth of the rain in millimeters can be read from the side of the container at least once a day (usually at 9:00a.m). A records is kept of the amount of rain (if any) which has fallen during the past 24 hours. At the end of a month the daily amount rainfall records are added together and this gives, of course, the total amount of rainfall for that month. Focus Mean monthly rainfall:it is calculated by adding all the amounts of rainfall on daily basis for the month and dividing the sum by the number of days of the month. Total annual rainfall: it is calculated by adding the amounts rainfall of the 12 months. Mean annual rainfall: it is calculated by adding the annual amounts of rainfall for 35 years and dividing the sum by the number of those years. 53  Grade 9 | Geography C. Measuring and Recording Air Pressure Air is made up of a number of mixed gases and has weight. It therefore exerts a pressure on the earth’s surface which varies from place to place and from time to time. This force that presses on the surface of any object can be fairly accurately measured. The instrument for measuring pressure is a barometer. The unit more commonly used for measuring pressure is called millibar and millimeter. At sea level, the mercury column is 1013.25 millibars, or 760 mm. d. Measuring and Recording Wind Speed Wind speed can be measured using an anemometer. The anemometer should be held at arm’s length, above the head so that the cups can rotate without any interference. e. Measuring and Recording Wind Direction Wind direction is reported by the direction it is blowing from, according to the compass. Wind blowing from the west is travelling eastwards so is called a westerly wind, not an easterly wind. Wind direction is often observed using a wind vane.