Geosystems: An Introduction to Physical Geography - Chapter 9 - Water Resources (PDF)

Geosystems: An Introduction to Physical Geography Updated Fourth Canadian Edition Chapter 9 Water Resources Copyright © 2019 Pearson Canada Inc. 2-1 Learning Objectives (1...

Geosystems: An Introduction to Physical Geography Updated Fourth Canadian Edition Chapter 9 Water Resources Copyright © 2019 Pearson Canada Inc. 2-1 Learning Objectives (1 of 2) Describe the origin of earth’s waters, report the quantity of water that exists today, and list the locations of Earth’s freshwater supply. Illustrate the hydrologic cycle with a simple sketch, and label it with definitions for each water pathway. Construct the water-budget equation, define each of the components, and explain its use. Learning Objectives (2 of 2) Discuss water storage in lakes and wetlands, and describe several large water projects involving hydroelectric power production. Describe the nature of groundwater, and define the elements of the groundwater environment. Evaluate the Canadian water budget, and identify critical aspects of present and future freshwater supplies. Water Resources The chapter discusses the origin and distribution of water on Earth, the hydrologic cycle, and a water-budget approach to understand global water balance. It explores surface and groundwater resources, discusses water quantity and quality, and concludes by addressing the importance of water quantity and quality in irrigation, industrial, and municipal uses. Water on Earth Earth's hydrosphere contains 1.36 billion cubic kilometers of water. Water originates from icy comets and planetesimals. In 2007, Spitzer Space Telescope observed water vapour and ice during planet formation 1000 light- years from Earth. Water migration and outgasses occur during planet formation. Water on Earth Water and water vapor emerge from deep layers below the Earth's surface, releasing in the form of gas. In the early atmosphere, outgassed water vapor condensed and fell to Earth in torrential rains. Land temperatures had to drop below 100°C for water to remain on Earth's surface, a process that occurred 3.8 billion years ago. The lowest places filled with water, forming ponds, lakes, seas, and oceans. Massive water flows washed over the landscape, carrying both dissolved and solid materials to these bodies. Outgassing of water continues today, visible in volcanic eruptions, geysers, and surface seepage. Water Outgassing from the Crust emerge from layers deep within and below the crust We can LOSE water to space and land when forming new compounds temperatures with other elements! < 100oC Replaced by more water emerging from the Earth Worldwide Equilibrium Water is the most common compound on Earth's surface, with a steady-state equilibrium due to constant gains and losses. Gains occur from pristine water emerging from Earth's crust, while losses occur from water dissociation into hydrogen and oxygen, escaping Earth's gravity, or breaking down and forming new compounds. The amount of water stored in glaciers and ice sheets varies, leading to periodic global sea level changes. Eustasy refers to changes in global sea level caused by changes in ocean water volume. Glacial ice melt is a key factor in these changes, with cooler climatic conditions lowering sea levels and warmer periods increasing sea level. Current global sea level rise is accelerating due to higher temperatures melting more ice and ocean water thermally expanding.  Distribution of Earth’s Water Today 1 Earth's continental land predominantly in Northern Hemisphere. 2 Water dominates surface in Southern Hemisphere. 3 Earth appears to have an oceanic and land hemisphere. Distribution of Earth’s Water Today Oceans contain 97.22% of all water, with 48% in the Pacific Ocean. 2.78% is nonoceanic freshwater, either surface or subsurface. Ice sheets and glaciers contain the most freshwater. Groundwater is the second largest amount. Less than 1% of freshwater is in lakes, rivers, and streams. The Hydrologic Cycle The hydrologic cycle is a global system of water, water vapour, ice, and energy. It circulates and transforms water across Earth's lower atmosphere, hydrosphere, biosphere, and lithosphere. The cycle is divided into three components: atmosphere, surface, and subsurface. Water's residence time in each component varies, with short periods in the atmosphere and longer periods in deep-ocean circulation, groundwater, and glacial ice. Slower parts of the cycle can buffer during periods of water shortage. Water in the Atmosphere Figure 9.4: Simplified model with water volume estimates. Ocean as starting point for discussion. Over 97% of Earth's water in oceans. 86% of Earth's evaporation occurs over oceans. Evaporation: net movement of free water molecules from wet surface into less than saturated air.  86 +14 = 100 78 + 22 = 100 20 = 8 + 12 Figure 9.4 The hydrologic cycle model Water travels endlessly through the hydrosphere, atmosphere, lithosphere, and biosphere. The triangles show global average values as percentages. Note that all evaporation (YELLOW) (86% + 14% = 100%) equals all precipitation (BLUE) (78% + 22% = 100%), and advection in the atmosphere is balanced by when all of Earth is considered. surface runoff and subsurface groundwater flow Water in the Atmosphere Water from land environments, including soil, passes through plant roots and leaves through transpiration. Transpiration releases water to the atmosphere through stomata in leaves. Control cells around stomata conserve or release water. A single tree can transpire hundreds of litres of water on a hot day, a forest millions. Together, evapotranspiration represents 14% of the water entering Earth's atmosphere. Water in the Atmosphere 1 86% of ocean evaporation combines with 12% from land to produce 78% of precipitation. 2 The remaining 20% of ocean evaporation and 2% of land-derived moisture produce 22% of precipitation. 3 The oceanic portion of the cycle contributes to the majority of continental precipitation. 4 Variations in the cycle across regions can lead to water surpluses and shortages. Water at the Surface Rain flows overland or soaks into soil. Interception occurs, with precipitation landing on vegetation or ground cover. Stem flow refers to water draining across plant leaves and stems to the ground. Throughfall refers to precipitation falling directly to the ground, including non-stem flow drips. Snow can accumulate for hours or days before melting or remain in the snowpack throughout winter. Water at the Surface 1 Water soaks into subsurface through infiltration or soil surface penetration after rain or snowmelt. If impermeable, water flows 2 downslope as overland flow or surface runoff. 3 Overland flow also occurs when soil is fully infiltrated and saturated. 4 Excess water may remain in puddles or ponds or form channels, forming streamflow. Water at the Surface 1 8% of water movement occurs on or through land. 2 95% of water movement comes from surface waters washing across land. 3 Only 5% is slow-moving subsurface groundwater. 4 Rivers and streams are dynamic, fast-moving compared to subsurface groundwater. Water in the Subsurface 1 Water infiltrates subsurface through percolation, a slow passage through porous substances. 2 Soil-moisture zone contains subsurface water accessible to plant roots. 3 Water bound to soil affects availability to plants. 4 76% of precipitation infiltrates subsurface, with 85% returning to the atmosphere via evaporation or transpiration. Water in the Subsurface Soil saturation leads to gravitational water percolating into deeper groundwater. The water table is the top of this zone, where soil spaces are completely filled with water. Water discharges at the intersection of the water table and stream channel, producing base flow, which includes groundwater. Streams and groundwater eventually flow into oceans, continuing the hydrologic cycle. Some streams flow into closed lake basins, where water evaporates or soaks into the ground. Groundwater flows slowly towards the sea, intersecting the surface or seeping underground. Water in the Subsurface Source Water Budgets and Resource Analysis 1 Can establish a water budget for any Earth's surface area. 2 Measures input and distribution of precipitation and evapotranspiration. 3 Includes evaporation, transpiration, and surface runoff. 4 Includes moisture stored in the soil- moisture zone. 5 Covers any time frame from minutes to years. Water Budgets and Resource Analysis 1 Water budget functions like a money budget, balancing precipitation and evaporation, transpiration, and runoff. 2 Soil-moisture storage acts as a savings account, accepting deposits and yielding withdrawals of water. 3 Water budgets can result in surplus or deficit if not met, leading to crop yields. 4 Thornthwaite developed a methodology for solving irrigation and water use problems. 5 He recognized the relationship between water supply and demand varies with climate. Components of the Water Budget Soil Water Change Rate: ∆𝑆 = 𝑃 − 𝐸𝑇 ∆𝑡 ∆ S = change in soil moisture ∆ t = change in time P = precipitation ET = evapotranspiration. Water Supply: Precipitation 1 Provides moisture to Earth's surface in various forms like rain, snow, or hail. 2 Rain gauge collects rainfall and snowfall for depth, weight, or volume measurement. 3 Wind shield reduces underestimation by catching raindrops that arrive at an angle. Water Supply: Precipitation Precipitation Measurements Worldwide 1 Over 100,000 locations monitored. 2 Global annual precipitation averages map displayed.  Water Demand: Potential Evapotranspiration Evapotranspiration is the actual water expenditure to the atmosphere. Potential evapotranspiration (PE) is the amount of water that would evaporate and transpire under optimal moisture conditions. A dry bowl illustrates the concept: if the bowl could be replenished with water, the total water demand would be PE. If the bowl dries out, the unmet PE is the water deficit. 𝐴𝐸 = 𝑃𝐸 − 𝑑𝑒𝑓𝑖𝑐𝑖𝑡 Subtracting the deficit from PE yields actual evapotranspiration (AE). Water Demand: Potential Evapotranspiration Evapotranspiration measurement using evaporation pan or evaporimeter Automatic replacement of water in evaporation pan. Lysimeter: Isolates representative soil, subsoil, and plant cover for moisture measurement. Rain gauge: Measures precipitation input next to lysimeter. Water Demand: Potential Evapotranspiration Thornthwaite's indirect method estimates PE for midlatitude locations using mean air temperature and daylength. Works well for large-scale regional applications using data from hourly, daily, monthly, or annual time frames. Works better in some climates than others. PE values for the United States and Canada are presented in Figure 9.8. Higher values occur in the South, with highest readings in the Southwest. Lower PE values are found at higher latitudes and elevations. Porosity Source Water Storage: Soil Moisture Soil-moisture storage (ST) is the volume of water accessible to plant roots in the subsurface soil-moisture zone. ST is a savings account of water that receives deposits and provides for withdrawals. The soil-moisture environment includes three categories of water: hygroscopic, capillary, and gravitational. Only hygroscopic and capillary water remain in the soil-moisture zone. Types of Soil Moisture ET = 0 ET ≈ >0, 0) Deficit phase: Storage is less than full There is utilization (plants are growing, there is evaporation), PE >0) Calculating a Water Budget Drought: The Water Deficit Meteorological Drought: Defined by the degree of dryness and duration of dry conditions. Region-specific due to differing atmospheric conditions. Agricultural Drought: Causes by shortages of precipitation and soil moisture affecting crop yields. Losses can be significant, running in the tens of billions of dollars annually in North America. Drought: The Water Deficit Hydrological Drought: Effects of precipitation shortages on water supply. Causes by decreased streamflow, drop in reservoir levels, decline in mountain snowpack, and increase in groundwater mining. Socioeconomic Drought: Results when reduced water supply exceeds demand for goods or services. Considers water rationing, wildfire events, loss of life, and other widespread impacts of water shortfalls. Drought: The Water Deficit Drought is a natural and recurring climate feature, especially in the U.S. Southwest. Scientists are indicating that increased aridity in the region is linked to global climate change and expansion of subtropical dry zones. Human-caused warming and natural climate variability are causing a trend towards lasting drought. Droughts previously linked to sea-surface temperature changes in the tropical Pacific Ocean will continue, worsened by climate change and expansion of the hot, dry subtropical high-pressure system and summertime continental tropical air mass. This shift of Earth's primary circulation systems and semi-permanent drought into a region of steady population growth and urbanization necessitates urgent water- resource planning. Drought: The Water Deficit Australia experienced its worst drought in 110 years, linked to record high temperatures. The Horn of Africa, including Somalia and Ethiopia, experienced its worst drought in 60 years and food crisis in 2010 and 2011. Drought patterns in east Africa are linked to sea- surface temperature patterns in the Indian Ocean. In 2012, the U.S. Department of Agriculture declared nearly one-third of all counties federal disaster areas due to drought conditions. 16 of the 16 droughts from 1980 to 2011 cost over $1 billion each, making drought one of the costliest U.S. weather events. Surface Water Resources Earth's surface water distribution is uneven. Large-scale management projects are used to redistribute water resources geographically or through time. This reduces deficits, holds surpluses for later release, and improves water availability. Freshwater is primarily found in snow, ice, rivers, lakes, and wetlands. Surface water is also stored in reservoirs, artificial lakes formed by dams on rivers. Earth's Largest Streamflow Volumes Largest within and adjacent to tropics. Reflects ITCZ's continual rainfall. Lower streamflow regions in subtropical deserts, rain-shadow areas, and continental interiors. Snow and Ice Glaciers, permafrost, and polar ice store the largest amount of surface freshwater on Earth. Seasonal melting from glaciers and annual snowpack contribute to water supplies. Snowpack melting in reservoirs behind dams is a primary water source for humans worldwide. Rising temperatures are accelerating glacial melting rates, with some scientists predicting most glaciers will disappear by 2035. Climate change is causing mountain glaciers to recede faster than anywhere else, affecting water supplies in Asia's Tibetan Plateau. The Yangtze and Yellow Rivers, which supply water to approximately 520 million people in China, are affected by the worsening drought in western China. Disappearing glaciers will affect high-elevation water supplies, especially during the dry season. Snow and Ice Source Rivers and Lakes Freshwater lakes, fed by precipitation, streamflow, and groundwater, store about 125 000 km3, or 0.33% of Earth's surface freshwater. 80% of this volume is in 40 of the largest lakes, and 50% is in 7 lakes. Lake Baikal in Siberian Russia holds the greatest single volume of lake water, containing almost as much as all five North American Great Lakes combined. Small lakes make up about one-fourth of global freshwater lake storage. Saline lakes and salty inland seas, not connected to the ocean, contain about 104,000 km3 of water. Examples include Utah’s Great Salt Lake, California’s Mono Lake and Salton Sea, Southwest Asia’s Caspian and Aral Seas, and the Dead Sea between Israel and Jordan. Rivers and Lakes Effects of Climate Change on Lakes Rising air temperatures are affecting global lakes, with some rising due to glacial ice melting and others falling due to drought and high evaporation rates. Longer summers alter the thermal structure of lakes, affecting normal mixing between deep and surface waters. Slowing or stopping mixing threatens continued decline of fish stocks. Effects of Climate Change on Lakes Lake Tahoe in the Sierra Nevada is warming at 1.3 C° per decade, with the highest rate in the upper 10m. Nonnative, invasive species like large- mouth bass, carp, and Asian clam are increasing in warming lakes, while cold- water species are declining. Lake Tanganyika in East Africa, surrounded by 10 million people, has risen to 26°C, the highest in a 1500-year climate record. Hydroelectric Power Reservoirs, or lakes, are formed by dams on rivers, with an estimated global volume of 5000 km3. The world's largest reservoir by volume is Lake Kariba in Africa. Dam construction serves flood control and water-supply storage, but also generates hydroelectric power, which supplies nearly one-fifth of the world's electricity. Hydropower is a highly variable source of renewable energy due to its dependence on precipitation. Hydroelectric Power China's Three Gorges Dam, the world's largest, is 2.3 km long and 185 m high. Relocation of over 1.2 million people to accommodate the 600-km-long reservoir upstream from the dam. Project involved environmental, historical, and cultural losses. Benefits include flood control, water storage, and electrical power production. Reservoir filled to its design capacity in October 2012, but potential water pollution and landslides may necessitate additional 300,000 relocations. Hydroelectric Power Significant hydroelectric projects in Canada include the Nelson River project in Manitoba, Churchill Falls project in Newfoundland and Labrador, and the $12 billion Gull Island Dam in Québec. These projects face engineering and political issues. In the US, hydropower accounted for 8% of total electricity production in 2011, with significant environmental impacts. Many large hydropower projects are old and production is declining. Worldwide, hydropower is increasing, with several large projects proposed and under construction in Brazil. Hydroelectric Power Pipelines and aqueducts are crucial for water transfer in dry regions. The California Water Project uses storage reservoirs, aqueducts, and pumping plants to adjust water budget. Winter runoff is held back for summer release, and water is pumped from northern to southern parts. The California Aqueduct, completed in 1971, flows from the Sacramento River delta to Los Angeles, servicing irrigated agriculture. The Central Arizona Project moves water from the Colorado River to Phoenix and Tucson. Wetlands Wetlands are areas permanently or seasonally saturated with water, characterized by vegetation adapted to gleysolic soils (soils saturated long enough to develop anaerobic, or “oxygen-free,” conditions). Wetlands can contain freshwater or saltwater. Types of wetlands include marshes, swamps, bogs, and peatlands. Wetlands are significant sources of freshwater and recharge groundwater supplies. Wetlands They absorb and distribute floodwaters when rivers flow over their banks. Major examples include the Amazon River floodplain, which stores water and mitigates flooding. Wetlands improve water quality by trapping sediment and removing nutrients and pollutants. Constructed wetlands are increasingly used for water purification. Source Groundwater Resources Groundwater is the largest potential freshwater source on Earth, larger than all surface lakes and streams combined. It covers an area of approximately 83,400,000 km3, equivalent to 70 times all freshwater lakes worldwide. Groundwater is tied to surface supplies for recharge through soil and rock pores. Its accumulation occurred over millions of years, necessitating careful management to prevent depletion with excessive short-term demands. Groundwater Resources Groundwater supplies 80% of global irrigation and drinking water. Polluted groundwater poses a threat to water quality and global food security. Overconsumption depletes groundwater volume beyond natural replenishment rates. 50% of the U.S. population uses groundwater for freshwater. In some states, groundwater supplies 85% of water needs, with rural areas having 100%. Annual groundwater withdrawal in Canada and the U.S. increased over 150% between 1950 and 2000. Groundwater Resources Areas of the United States indicated in dark blue are underlain by productive aquifers capable of yielding freshwater to wells at 3.33 L/s or more (for Canada, 0.4 L/s). Source The Groundwater Environment Precipitation is the primary source of groundwater, moving downward as gravitational water from the soil-moisture zone. Water moves through the unsaturated zone, the zone of aeration, where some pore spaces contain air. Gravitational water accumulates in the saturated zone, where soil pore spaces are completely filled with water. The zone of saturation stores water in its numerous pores and voids, bounded by an impermeable layer of rock. The upper limit of the saturation zone is the water table, which drives groundwater movement towards areas of lower elevation and pressure. Aquifers and Wells Aquifers are subsurface layers of permeable rock or unconsolidated materials that allow groundwater to flow. Unconfined aquifers have a permeable layer above and an impermeable one beneath. Confined aquifers are bounded by impermeable layers of rock or unconsolidated materials. An aquitard is a layer with low permeability but cannot conduct usable amounts of water. The zone of saturation may include the saturated portion of the aquifer and part of the underlying aquiclude. Aquifers and Wells Humans extract groundwater through wells drilled downwards until they penetrate the water table. Shallow drilling results in a "dry well," while deep drilling can lead to impermeable layers and less water. Water in unconfined aquifers needs pumping to rise above the water table. In confined aquifers, water under pressure creates a potentiometric surface for self-rise. the height that water would rise in a well penetrating the pressurized aquifer system Aquifers and Wells Potentiometric surface can be above ground level. Artesian water, confined under pressure, can rise in wells. Artesian wells are common in the Artois area in France. In some wells, pressure may be inadequate, requiring pumping to reach surface.  Aquifers and Wells Restricted recharge area Recharge area of of a confined an unconfined Unconfined aquifers have a aquifer aquifer recharge area above the entire aquifer, allowing water to percolate down to the water table. Confined aquifers have a more restricted recharge area, leading to groundwater contamination. Pollution from the confined area, like leakage from a disposal pond, can contaminate nearby wells. Perched Aquifer  Unconfined aquifer Well in unconfined Confined aquifer aquifer Confining layer Well in confined aquifer Recharge area Potentiometric Water table surface Flowing artesian well Groundwater at the Surface Water flows outward in springs, streams, lakes, and wetlands where the water table intersects the ground surface. Springs are common in karst environments where water dissolves rock and flows underground. Hot springs are common in volcanic environments where water is heated underground before emerging at the surface. In the southwestern United States, a ciénega is a marsh where groundwater seeps to the surface. Groundwater at the Surface Groundwater interacts with streamflow to provide base flow during dry periods and supplement it during periods of water surplus. In humid climates, the water table is higher than the stream, supplying a continuous base flow to a stream, an effluent stream (a). In drier climates, the water table is lower than the stream, causing influent conditions where streamflow feeds groundwater, sustaining deep-rooted vegetation (b). Overuse of Groundwater Drawdown occurs when pumping rate exceeds water replenishment flow or horizontal flow around the well. This results in a cone of depression, lowering the water table around the well. Over-pumping near the ocean or seacoast can cause freshwater to migrate inland, contaminating wells near the shore (saltwater intrusion). Pumping freshwater back into the aquifer may halt seawater intrusion, but once contaminated, reclaiming the aquifer becomes difficult. Source  Overuse of Groundwater Groundwater mining involves utilizing aquifers beyond their flow and recharge capacities. Waterloo, Ontario, is the largest urban groundwater municipality in Canada, relying on groundwater for municipal supplies. Depletion of groundwater aquifers has led to conservation efforts and Recovery would take at exploration of other water sources. least 1000 years if Chronic groundwater overdrafts occur in groundwater mining the Midwest, West, lower Mississippi stopped today! Valley, Florida, and eastern Washington. Irrigated agriculture is unsustainable on the Groundwater mining is particularly southern High Plains concerning for the High Plains Aquifer. Recharge Times Overuse of Groundwater Overuse of groundwater can draw contaminants toward the well as in this example Septic effluent initially flowed downhill, away from the well The cone of depression and drawdown causes the septic effluent to flow uphill, toward the well  Desalination Desalination removes organic compounds, debris, and salinity from seawater, brackish water, and saline groundwater. Over 14,000 desalination plants worldwide, with freshwater production projected to nearly double between 2010 and 2020. 50% of all desalination plants are in the Middle East, with the Jebel Ali Desalination Plant in the UAE being the largest. Saudi Arabia's 30 desalination plants Jebel Ali Power and Desalination Plant supply 70% of its drinking water needs, reducing groundwater mining and saltwater intrusion issues. Pollution of Groundwater Surface water pollution contaminates groundwater during recharge and slow-moving groundwater remains polluted virtually forever. Pollution sources include industrial injection wells, septic tank outflows, hazardous-waste disposal sites, industrial toxic waste, agricultural residues, and urban solid-waste landfills. Suspected leakage from 10,000 underground gasoline storage tanks at U.S. gasoline stations is believed to be contaminating local water supplies with cancer-causing gasoline additives. Abbotsford Aquifer There are numerous potential sources of contamination including: agricultural handling of manure fertilizer use pesticide use septic systems fuel storage tanks surface mining activities stormwater runoff industrial activities urban gardening practices Source Pollution of Groundwater About 35% of groundwater pollution comes from point sources, while 65% is nonpoint source, coming from a broad area. Nitrates contaminate nearly all groundwater under agricultural land in Canada, below Canadian drinking water quality guidelines. The 1996 State of Canada’s Environment Report noted nitrate levels were more than four times greater than Canadian drinking water guidelines in some areas. OSDS = Open Source Dissemination System Fracking Geoscientists identify economically viable oil or gas areas. Methane is a significant natural gas reservoir in shale deposits. Canadian shale plays recognized in Maritime Provinces, Québec and Ontario, Prairie Provinces, and British Columbia. Prospective plays underlie much of Alberta. Fracking Horizontal drilling techniques and hydraulic fracturing have opened access to large amounts of natural gas. Horizontal drilling exposes more rock, allowing more gas release. A pressurized fluid is pumped into the well to break up the rock, using 90% water, 9% sand or glass beads, and 1% chemical additives. The specific chemicals used are yet undisclosed by the industry. Gas flows up the well to be collected at the surface. Fracking Fracking uses large quantities of water, with each well system consuming approximately 15 million litres. It produces toxic wastewater, often stored in wells or containment ponds. Leaks or failures in pond retaining walls can spill pollutants into surface water and groundwater. Methane gas leaks around well casings can cause contamination, flammable tap water, and explosions. Methane leak rates in many fracking areas exceed standards, erasing the advantage of gas mining over coal. Conflicts between production companies and groups like First Nations people, ranchers, farmers, and environmentalists have occurred.  Methane contributes to air pollution and global climate change. Injection of fluid into wastewater wells linked to earthquake activity and ground instability. Impacts vary on air, water, land, and living Earth systems. Unknown environmental effects of shale gas extraction require further scientific study.  Our Water Supply Human thirst for adequate water supplies is a major issue in the 21st century. Increases in per capita water use double the rate of population growth. Accessible water supplies are not well correlated with population distribution or growth regions. Table 9.1 shows unevenness of Earth's water supply, including population, land area, annual streamflow, and projected population change. The adequacy of Earth's water supply is tied to climatic variability, water usage, development, affluence, and per capita consumption. TABLE 9.1 Regional Comparison of Factors Influencing Global Water Supply *Includes Canada, Mexico, and the United States. **CO2 data for U.S. and Canada; Mexico per capita emissions are 4.0 tonnes. Note: Population data from 2012 World Population Data Sheet (Washington, DC: Population Reference Bureau, 2012). CO2 data from PRB 2009. Our Water Supply North America's annual streamflow is significantly lower than Asia’s and has only 6.6% of the world's population. In northern China, 550 million people in approximately 500 cities lack adequate water supplies, costing the country over $35 billion a year. In Africa, 56 countries share over 50 river and lake watersheds, with population growth and increased irrigation enhancing water demand. 12 African countries currently experience water stress, while 14 have water scarcity. Groundwater reserves on the African continent are larger than previously thought, but with ongoing drought, these reserves could be quickly depleted. Water shortages increase international conflict, endanger public health, reduce agricultural productivity, and damage ecological systems. Future political agendas will focus on water-resource stress related to decreasing quantity and quality. Water Supply in Canada Derives from surface and groundwater sources. About 9% of Earth's renewable water is distributed over 7% of Earth's landmass. Accessible sources include rivers, lakes, ponds, reservoirs, groundwater aquifers, snowpack, glaciers, ice fields, and precipitation. Measurements of precipitation across Canada are challenging due to vast landmass hydrology. Despite being relatively “water rich” and a “developed country”, many First Nations communities lack adequate drinking water – a National Shame Water Supply in Canada Diagram shows streamflow distribution in Canada, illustrating low flows, peak flows, and runoff. Peak flows occur earlier in the year to the south and later to the north, often causing spring flooding. Surface runoff (runoff plus streamflow) varies between 75,000 m/s in low flow times to over 134,550 m/s in high flow times. Water Supply in Canada 60% of Canada's freshwater drains to the north, while 85% of the population lives within 300 km of the southern border. Urbanization is increasing the gap between supply and demand, putting pressure on all freshwater sources. Demands for domestic water supplies, agriculture, industry, and streamflow maintenance are increasing. Climate change's uncertain effects add to the stress. Despite these challenges, many Canadians believe governments will protect and sustain the freshwater supply. Water Withdrawal and Consumption Rivers and streams make up 0.003% of Earth's surface water, but they account for about four-fifths of the surplus 1700 km3/yr. Water withdrawal involves the removal or diversion of water from surface or groundwater supplies, followed by its return. Examples include industry, agriculture, and municipal use. Consumptive use involves permanent removal of water from the immediate water environment, not returned, and not available for a second or third use. Instream use involves uses of streamflow while it remains in the channel, including transportation, waste dilution, hydroelectric power production, fishing, recreation, and ecosystem maintenance. Returned water becomes part of all water systems downstream, with Canada using only 9% of its withdrawn water for agriculture and 80% for industry. Future Considerations Water budgets reveal water resource limits. Changes in one side must balance the other, such as increased demand for surplus water. Population growth and economic development increase demand for water. World population growth since 1970 reduced per capita water supplies by a third. Pollution limits the water-resource base, affecting health and growth. Nations share water resources, creating problems. Streamflow represents a global commons, with 145 countries sharing a river basin. The Human Denominator Water Resources → Humans Freshwater, stored in lakes, rivers, and groundwater, is a critical resource for human society and life on Earth. Drought results in water deficits, decreasing regional water supplies and causing declines in agriculture. Humans → Water Resources Climate change affects lake thermal structure, and associated organisms. Water projects (dams and diversions) redistribute water over space and time. Groundwater overuse and pollution deplete and degrade the resource, with side effects such as collapsed aquifers and saltwater contamination. The Human Denominator Issues for the 21st Century Maintaining adequate water quantity and quality will be a major issue. Desalination will increase to augment freshwater supplies. Hydropower is a renewable energy resource; however, drought-related streamflow declines and drops in reservoir storage interfere with production. Drought in some regions will intensify, with related pressure on groundwater and surface water supplies. In the next 50 years, water availability per person will drop as population increases, and continuing economic development will increase water demand. Quizlets Review Questions 1. Approximately where and when did Earth’s waters originate? 2. Describe the location of Earth’s water, both oceanic and fresh. What is the largest repository of freshwater at this time? In what ways is this distribution of water significant to modern society? 3. Sketch and explain a simplified model of the complex flows of water on Earth—the hydrologic cycle. 4. Compare precipitation and evaporation volumes from the ocean with those over land. Describe advection flows of moisture and countering surface and subsurface runoff. Review Questions 5. What are the components of the water-balance equation? Construct the equation and place each term’s definition below its abbreviation in the equation. 6. What is potential evapotranspiration (PE)? How do we go about estimating this potential rate? What factors did Thornthwaite use to determine this value? 7. Explain the operation of soil-moisture utilization and soil-moisture recharge. Include discussion of capillary water and the field capacity and wilting point concepts. Review Questions 8. In the case of silt-loam soil from Figure 9.9, roughly what is the available water capacity? How is this value derived? 9. Describe the four types of drought. 10. What changes occur along rivers as a result of the construction of large hydropower facilities? Review Questions 11. Are groundwater resources independent of surface supplies, or are the two interrelated? Explain your answer. 12. Make a simple sketch of the subsurface environment, labeling the various zones leading down to an unconfined aquifer. Then add a confined aquifer to the sketch. Compare and contrast the two. 13. Describe the consequences of overuse of groundwater. Give specific examples. 14. Discuss the methods by which we can tell which way groundwater flows. Review Questions 15. Describe and discuss the ways in which an aquifer can become contaminated. Give specific examples. 16. Describe and discuss the ways in which groundwater interacts with various types of surface waters. 17. Describe and discuss the water balance equation and its various components. 18. Describe and discuss two different geological occurrences of aquifers. Summary of Chapter 9 (1 of 3) Water molecules came from within Earth over a period of billions of years in the outgassing process. Water covers about 71% of Earth. The hydrologic cycle is a model of Earth’s water system, which has operated for billions of years from the lower atmosphere to several kilometers beneath Earth’s surface. Evaporation is the net movement of free water molecules away from a wet surface into air. Transpiration is the movement of water through plants and back into the atmosphere. Evaporation and transpiration are combined into one term— evapotranspiration. Summary of Chapter 9 (2 of 3) A water budget can be established for any area of Earth’s surface by measuring the precipitation input and the output of various water demands in the area considered. If demands are met and extra water remains, a surplus occurs. If demand exceeds supply, a deficit results. Groundwater lies beneath the surface beyond the soil moisture root zone. Excess surface water moves through the zone of aeration, where soil is not saturated. Eventually, the water reaches the saturation zone. The upper limit of the water that collects in the saturation zone is the water table. Summary of Chapter 9 (3 of 3) An aquifer is a rock layer that is permeable to groundwater flow in usable amounts. An unconfined aquifer has a permeable layer on top and an impermeable one beneath. A confined aquifer is bounded above and below by impermeable layers of rock or unconsolidated material.