Groundwater and Aquifer Depletion
While floodwater is one way to replenish global water resources, floodwater requires large-scale management and coordination of water systems including reservoirs and dams. Water for irrigation, industry, and household uses must be delivered in controlled quantities at specific times, making floodwater an impractical solution to renewing water resources without the necessary management in place.
Also, as the human population has increased, so has trade among nations and more water is used to produce these goods and services. As a result of this increase in environmental trade and urbanization, countries have tried to overproduce in an effort to maintain a competitive edge in the global marketplace. This has placed a burden on the groundwater sources in many nations that have overpumped aquifers in an effort to increase production and trade. This is most notable in the agricultural community. For example, the three main grain producers, China, United States, and India, have all felt the effects of overpumping, or pumping that exceeds the long-term average rate of replenishment. Ultimately, overpumping can lead to a depletion of aquifers and consumption of aquifer reserves, which may lead to cutbacks in grain harvests. Evidence of substantial and widespread drawdown of the piezometric surface beneath many Asian cities, as a result of heavy exploitation of aquifers, also has been accumulating since the early 1970s.
The increase in agricultural production, in both crops and livestock, is significant as much of the water that is used for production cannot be recovered or reused; in essence, it is consumed. According to the United Nations Educational, Scientific and Cultural Organization (UNESCO), world agriculture consumes 70% of the freshwater withdrawn per year.1271
Increased crop production and irrigation negatively affects soil quality and water runoff. Irrigation causes soil erosion, which diminishes the soil quality by reducing soil depth and soil nutrients. Other problems and failures of irrigated agriculture include groundwater overdraft, water quality reduction, water logging, and salinization.133! while these various forms of soil degradation are proven to affect water resources, on a global level, they are very hard to track.191
Increased livestock production directly and indirectly affects the depletion of water resources in that not only do livestock directly consume freshwater but water is also consumed in the production of grains that are fed to the livestock. According to the U.S. Department of Agriculture (USDA), increased crop and livestock production during the next five to seven decades will significantly increase the demand on all water resources, especially in the western, southern, and central United States and in many regions of the world with low rainfall.1271 Strategies such as crop rotation, replacement of trees and shrubs, soil maintenance, and the use of organic mulch promote water conservation by limiting the damage done by crop production.1271
Appropriate water pricing is important for improved water demand and conservation of water.1271 The relatively high cost of treating and delivering water has led many world governments to subsidize water for agricultural and household use. For example, some U.S. farmers pay as little as $0.01 to $0.05 per 1000 L used in irrigation, while the public pays $0.30 to $0.80 per 1000 L treated water for personal use.1341 According to the World Bank,1351 the objectives of fair water pricing are 1) to seek revenue to pay for the operations and maintenance of water availability; 2) to improve water use efficiency; and 3) to recover the full costs of water pumping and treatment.1361
Finally, there is a growing scientific consensus that the buildup of greenhouse gases in the atmosphere is warming the Earth.151 The continued loss of forests and other vegetation and the accumulation of carbon dioxide, methane gas, and nitrous oxide in the atmosphere are projected to lead to global climate change or global warming. Over time, such changes may alter precipitation and temperature patterns throughout the world.1271 These temperature changes might increase soil erosion and deforestation, which could result in greater reductions in water availability worldwide. Salati and Vose1371 claim that regional forest clearance would have severe climatic consequences. Because of the high proportion of water recycled by the rainforest, deforestation would significantly lessen rainfall and increase temperatures.