5.1 Water cycle and fresh water supply  (Page 8/47)

Another water resource problem associated with groundwater mining is saltwater intrusion    , where overpumping of fresh water aquifers near ocean coastlines causes saltwater to enter fresh water zones. Saltwater intrusion is a significant problem in many coastal areas of the U.S. including Long Island, New York; Cape Cod, Massachusetts; and southeastern and Gulf Coastal states. The drop of the water table around a cone of depression in an unconfined aquifer can change the regional groundwater flow direction, which could send nearby pollution toward the pumping well instead of away from it. Finally, problems of subsidence (gradual sinking of the land surface over a large area) and sinkholes (rapid sinking of the land surface over a small area) can develop due to a drop in the water table.

The water supply crisis

The water crisis    refers to a global situation where people in many areas lack access to sufficient water or clean water or both. This section describes the global situation involving water shortages, also called water stress. The next section covers the water crisis involving water pollution. Figure Countries Facing Water Stress in 1995 and Projected in 2025 shows areas of the world experiencing water stress as defined by a high percentage of water withdrawal compared to total available water. Due to population growth the 2025 projection for global water stress is significantly worse than water stress levels in 1995. In general, water stress is greatest in areas with very low precipitation (major deserts) or large population density (e.g., India) or both. Future global warming could worsen the water crisis by shifting precipitation patterns away from humid areas and by melting mountain glaciers that recharge rivers downstream. Melting glaciers will also contribute to rising sea level, which will worsen saltwater intrusion in aquifers near ocean coastlines. Compounding the water crisis is the issue of social injustice; poor people generally get less access to clean water and commonly pay more for water than wealthy people.

According to a 2006 report by the United Nations Development Programme, in 2005, 700 million people (11% of the world’s population) lived under water stress with a per capita water supply below 1,700 m ³ /year Although 1,700 m ³ /year sounds like a lot of water for every person, it is the minimum amount that hydrologists consider is needed to grow food, support industry, and maintain the environment in general. (Watkins, 2006 ). Most of them live in the Middle East and North Africa. By 2025, the report projects that more than 3 billion people (about 40% of the world’s population) will live in water-stressed areas with the large increase coming mainly from China and India. The water crisis will also impact food production and our ability to feed the ever-growing population. We can expect future global tension and even conflict associated with water shortages and pollution. Historic and future areas of water conflict include the Middle East (Euphrates and Tigris River conflict among Turkey, Syria, and Iraq; Jordan River conflict among Israel, Lebanon, Jordan, and the Palestinian territories), Africa (Nile River conflict among Egypt, Ethiopia, and Sudan), Central Asia (Aral Sea conflict among Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, and Kyrgyzstan), and south Asia (Ganges River conflict between India and Pakistan).