Global Water Problems: Present and

Global Water Problems: Present and Future
The single biggest water problem worldwide is scarcity. In much of the world, existing water supplies are insufficient to meet all of the urban, industrial, agricultural, and environmental demands. The primary condition determining whether a region has a water surplus or experiences water scarcity is whether precipitation exceeds potential evaporation. In regions where potential evaporation exceeds precipitation, there is minimal runoff available to be intercepted and stored for later use, leading to a critical dependence on the timing and amount of rainfall. The regions of greatest concern due to water scarcity are those of the global Savannah zone, which extends through much of Africa, parts of Southeast Asia, and the middle of South America. Many of the countries in Savannah zones have rapidly growing populations and insufficient wealth to permit the importation of food to feed their inhabitants. In the absence of substantial assistance from other countries, these nations may face widespread starvation in the future.
One manifestation of scarcity is attributable to the economic forces that influence different uses of water. The value of water in urban and industrial uses is typically far larger than its value in agriculture. Environmental uses, which tend to be undervalued by markets and quasimarkets, usually have significantly less value than urban uses. As the world population increases by several billion or more over the next 30 years, market forces will cause a significant reallocation of water resources from the agricultural and environmental sectors to the urban sector. This will result in intensifying stress on water-based ecosystems and on the world's food production capacity.