Chapter 5

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University of Toronto Scarborough
Environmental Science
Jovan Stefanovic

Chapter 5, Water Scarcity Defining Scarcity Water scarcity has multiple aspects and diff definitions of scarcity try to capture one or more of these facets Falkenmark Indicator Falkenmark introduced a water crowding indicator: number of people sharing a unit of water - As this indicator increased, there would be an increase in societal water stresses - Later converted from people per unit water to water availability per capita - Current: focuses on how much water is availbel to meet the needs of each prson - Weakeness: doesnot take into account differences in water needs among different countries or regions : the thresholds apply to countries where conditions are conducive to rain-fed agriculture and to those regions where food must be grown using irrigation these two types of countries have different water needs yet they are tied to identical level of water availability WTA Inidcator WTA: withdrawal to availability, also called the criticality ratio Widely used indicator of water scarcity Ratio of annual water availability and uses the thresholds levels to define different levels of stress Takes into accounts different water needs of different countries by using water withdrawals as the numerator Draws our attentioan to when a country is using a large fraction of tis available water supply: at levels of 40% -- should expect systems such as ecosystem degradation etc Weaknesses: 1)Data quality: since the WTA indicator requires data on water use along with water availability---“subject to problems associated with collecting data on water use 2) Timing: diff countries have diff relationshops btwn annual and dry season water availability 3) appropriateness of water use: doesnot indicate whether the withdrawals are appropriate-i.e a poor country with poor infrastructure may appear unstressed by WTA indicator because its water withdrawal levels are so low. Falk indicator vs WTA indicator Falk indicator focuses on natural water endowment , WTA indicator focuses on how countries are using that endowment Therefore, a country with ample water resources per person by falk maybe considered stressed by the WTA indicator if it is using a great deal of water per person (i.e wasteful or export of water-intensive products) Assessing water scarcity at different scales Global water scarcity indicators for global: conclude earth is not water scarce Falk indicator: 3 3 global runoff: 42000 km per year per 6.7 bill people = 6300 m person per year WTA Indicator: 4077km per 42000 km per year = 9.7% ^ both are in no scarcity category Country Scale Falk Indicator Most countries are in the no scarcity category 45 countries have some level of water stress with 19 in severe scarcity category Highest-scarcity countries: Middle East, North Africa countries WTA indicator 67 countries have some level of water stress with 30nin severe category. A number of categories are withdrawing more than 100% of their TRWR either by using groundwater unsustainably or desalination or both More countries are considered water-scarce by the WTA indicator than by Falk indicator. Many countries have a reasonable level of water availability (Falk) but are using too much water (WTA) i.e U.S has abundant water resources but a WTA ratio that places it in slightly stressed category Grid Scale 2 fine-scale global models of water availability and use have been developed: Water Balance Model and WaterGAP2 model Each of these divide the earth in to a grid, 0.5 ° cells on a side and uses globally available data to calculate water availability and withdrawals within each grid scale Water availability : consists of runoff generated within the cell and run off from upstream Water withdrawals: for each cell calculated by sector Voro (2000) used Water Balance model to identify grids that exhibit severe water scarcity as per WTA indicator where withdrawal is over 40% Estimated number of people living in high-scarcity grid ells: 1.8 billion mostly in south Asia, Africa, Middle East,West North America. 0.45 billion people living in high-scarcity countries Voro argue that country-level estimates mask a huge amount of variability within countries esp large countries and that grid-cell estimates better reflect local water situation BUT since countries move water from water-rich area to water-poor areas, not clear whether 50km x 5o km grid cells are right scale for expressing actual water supply available to a pop. But there are envtal and financial costs to water transport—hence grid scale analysis can be best seen as identifying areas where these costs are large, hence no water transport. River Basin Scale river basin: natural unit for assessing water scarcity if to avoid interbrain transfers and move toward watershed management, then the inhabitant of a basin must live within the limits imposed by water availability by within the basin although water availability data readily accessible but water use is gathered at the country level—hence must rely on models Economic Water Scarcity Lack of access to water at household level Large num of people in developing countries donot have access to a reliable supply of safe water for the most basic domestic needs ^ not due to water scarcity at country-level : even the countries with the highest water scarcity have enough water to meet residential needs The house-hold scarcity is due to shortcomings in economic and institutional capacity: the lack of resources to build and maintain the infrastructure needed to supply with clean water Economic water scarcity: refers to situation where economic rather than physical constraints are limiting the development of water infrastructure and resutlign in lack of water availability to individual users The first IWMI indicator of economic water scarcity was based on how rapidly withdrawals needed to increase in the future to satisfy the demands of larger and more developed populations Countries that were not physciallyw ater scarce but needed to icnrese their withdrawals by more than 100% were cosndiered to have sever economic scarcity i.e Sub-Sharan Afric Countries that needed to increase their withdrawals by 25-100% were classified as experiencing a lesser degree of economic water scarcity The second IWMI indicator of economic scarcity is based on current extent of malnutrition since mal is linked to inadequate water infrastructure for irrigation. i.e Sub-Saharan, small parts of latin america . Groundwater Overdraft Groundwater is part of a countries TRWR When groundwater is used more rapidly than it is being recharged, water tables fall over time and variety of problems: 1) Costs increase as wells must be deepend and more energy must be used to pump water from greater depths 2) Irreversible subsidence of the and surface may cocur as pores that were filled with water collapse when the water is pumped out . this subsidence can be patchy and lead to infrastructure problems near the surface i.e buildings tilting . In coatal areas, subsidence can lead to rise in sea level and a increase in total flooding 3) A hydraulic gradient s created which can draw in polluted water fromnearby sites or in coastal areas draw in seawater to replace the freshwater pumped out (seawater intrusion).these contaminants make the remainder of the aquifer unusable. Euity problem ;those that are wealthy can dig deep and pump out groundwater, drying up wells of the neighbors hwo don’t have resources to deepen their wells and the poor neighbors may be paying for the water drawn from their own wells. Intergenerational equity problem: GW that is overpumped today is not available for use by the next generation. Advantages to groundwater use: 1) Does not require the damming
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