ENV200 Chapter 11 Notes

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School of Environment
Romila Verma

CHAPTER 11 – WATER: RESOURCES AND POLLUTION [11.3] WATER AVAILABILITY AND USE ­ Water availability determines the location and activities of humans on the earth ­ Renewable water supplies (e.g., surface water, shallow groundwater) are cleansed and replenished by the hydrologic cycle ­ Water is a renewable resource, but renewal takes time ­ The highest per capita water supplies occur in countries with wet climates and low population densities We use water for many purposes ­ Water can be recycled if its quality isn't degraded by use ­ Water withdrawal = the total amount of water taken from a water body o Much of this water can be returned to circulation in a reusable form ­ Water consumption = loss of water due to evaporation, absorption, or contamination ­ Agriculture uses 70% of total water withdrawal, worldwide o Most common type of irrigation in developing countries is to flood the whole field or run water in rows between crops  50% of this water is lost through evaporation or seepage from unlined irrigation canals bringing water to fields o Sprinklers are more efficient in distributing water, but are costly and energy-intensive o Water-efficient drip irrigation is even more efficient ­ Water is required to grow and prepare the food we eat Industrial and domestic uses tend to be far lower than agricultural use ­ Industrial water use represents 25% of total water withdrawal, worldwide o Cooling water for power plants is by far the largest single industrial use of water  Much of the cooling water can be recycled for other uses o Biofuel production is a rapidly growing demand for water ­ Domestic water use represents 6% of total water withdrawal, worldwide o Amount of water used per household varies depending on a country's wealth  People in developed countries consume on about ten times more water daily than those in developing countries  Poorer countries often can't afford the infrastructure to obtain and deliver water to citizens ­ Many attempts have been made to enhance local supplies and redistribute water o Cloud seeding = distributing condensation nuclei in humid air to help form raindrops  Effective, but essentially taking moisture from one area for the benefit of another o Desalination = removing salt and other minerals from seawater  Sometimes the principal source of water where energy and money are available but water is scarce [11.4] FRESHWATER SHORTAGES ­ Clean drinking water and basic sanitation are necessary to prevent communicable diseases and to maintain a healthy life o 1 billion people lack access to clean drinking water o 2.5 billion people lack basic sanitation ­ Water shortages are expected to become even worse Water scarcity is a growing problem ­ 1/3 of the world’s population lives in countries where water supplies don't meet everyone's minimum essential water needs o Local conditions can be much worse than the country-wide mean ­ Water use has been increasing about twice as fast as population growth over the past century o Conflicts are likely to increase as different countries compete for the same limited water supply (e.g., water wars) ­ Sometimes the problem isn’t the total amount of water but access to clean water o Results in a variety of diseases linked to contaminated water and lack of sanitation Living in an age of thirst ­ Global warming is expected to exacerbate water scarcity o Dry areas will get drier o Wet areas will be wetter ­ Drought = an extended period of consistently below average precipitation that has a substantial impact on ecosystems, agriculture, and economies o Dust Bowl (1930s)  Only lasted about 6 years  Wind stripped topsoil from millions of hectares of land  Billowing dust clouds turned day into night  People were forced to leave farms and migrate to other areas ­ John Wesley Powell o Concluded that there isn't enough water to support a large human population o Recommended that the political organization of the West be based on watersheds so that everyone in a given jurisdiction would be bound together by the available water  Farms should be limited to local surface-water supplies  Cities should be small, oasis settlements Groundwater supplies are being depleted ­ Groundwater provides 40% of the fresh water for agricultural and domestic use (e.g., drinking) in the United States ­ Overuse of groundwater supplies dries up wells, natural springs, and even groundwater-fed wetlands, rivers, and lakes ­ Sources of contamination o Pollution of aquifers through dumping of contaminants on recharge zones o Leaks through abandoned wells o Deliberate injection of toxic wastes ­ Aquifer depletion o Groundwater is being withdrawn from aquifers faster than natural recharge can replace it o On a local level, this causes a cone of depression in the water table o On a broader scale, excessive pumping can deplete a whole aquifer  Aquifers can take thousands of years to recharge  Aquifers are non-renewable resources ­ Aquifer collapse o Water withdrawal allows aquifers to collapse, followed by subsidence
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