Farmers and city planners are acutely aware of the need for a reliable water supply. Most of us take water for granted. After all, even though it sometimes doesn't rain when we want it too, there's water as near as the faucet - right? This view is shortsighted, and fails to take into account the long-term impact of lack of water, a condition called drought.
The earth is 75% water, so there should always be enough to go around. But, the fact is, over 97% of the earth's water is in the oceans, and because of its salinity, is unusuable. At any given time only about .001% of our water is in the atmosphere. The process of transfer of water from ocean to atmosphere to a usuable form, is called the hydrologic cycle. Disruption of this cycle, either through natural causes or man's mismanagement of his environment, leads to water shortage, or drought.
Prolonged drought can have long-term and possible irreversible consequences, environmentally and economically. From an economic standpoint, drought can cause low water supply, low agricultural yields (which leads to higher food prices or food shortages) and population displacement. The drought in America's Dust Bowl of the 1920s and 1930s caused massive movement of people from dried up farms in the Great Plains and caused an economic recession.
Worse, and probably least understood, is the impact prolonged drought has on our environment. When water levels are unnaturally low over long periods of time, it impacts the growth of plant species that had adapted to the availability of the water. Plants become susceptible to boring insects and disease, have less resistance to diseases and can suffer root death. Some plants, such as cacti, have adapted to a low water environment, but they are a habitat for specific insects and animals. When drought causes die-off of plant species, it also affects the other creatures that have used these plants for food and shelter. When smaller animals die or relocate, it impacts the larger animals that feed off them. Thus, a prolonged drought can alter or destroy biodiversity of a region.
Some of this change caused by alterations in the hydrologic cycle is normal and probably unavoidable. That which is due to human mismanagement, however, is within our power to change. The Dust Bowl, for instance, which altered the ecological and economic face of the Great Plains region of the United States, was a direct result of over farming and deforestation by farmers. If earth is to continue to be a home to our species, we must learn to live in harmony with all its creatures, and protect their habitats - lest we lose our own.