Severe drought is a natural event that results from disruptions of the water cycle, and that, in turn, interferes with the cycle of nutrients and flow of energy in ecosystems. During periodic onslaughts of drought, glacier melting is intensified, lakes and other water bodies dry up, and the groundwater level sinks, crops are destroyed and societies disrupted. Drought also greatly influences the development of ecosystems. Severe droughts cause widescale alterations in species composition, and major disruptions of ecological communities. As plants die, their roots are no longer able to hold the soil. This results in massive erosion of topsoil rich in nutrients and organic matter. During this period, succession is often set back to bare subsoil. Drought has very different hydrological causes and characteristics, and its effects are less spectacular than those of floods, but they are more insidious and lasting, since they are closely connected with endemic famine in the world, and may in addition undermine for many years the prosperity of an entire region (the case of the Sahel).
The drought in Africa lasted for much of the 1970's and 1980's and created a disaster out of an economic and social situation which was already serious. One of its worst effects is the increasing water shortage for human and animal consumption. As many as 21 out of the 24 food-aid dependent countries are also affected by water scarcity. In Mauritania, sand now covers 6 million extra hectares every year. Another 21 million hectares pass into zero productivity each year. In the last two decades Mauritania has lost 80% of its pasture to the sand. Chile lost 400,000 or 75% of its sheep population, experienced power shortages since electrical generation capacity was reduced by 20%, and faced increased unemployment as a result of the devastating drought in 1967-69. The 1971 Okinawan drought, the worst in history, destroyed sugar-cane and pineapple plantations and caused economic losses amounting to $10 million. During the whole 150 year period 1830-1980 the European and Asian parts of the USSR suffered severe drought damage (81 of those years were dry). Crop failures of 19% and 25% respectively were reported during the 1972 and 1975 droughts. During the last 200 years some 30 great droughts have scourged the USA.
In 1996, Oklahoma, Kansas and Texas ranchers suffered second driest period since the Dust Bowl in the 1930s. Absence of rain and blazing heat pushed thousands of them to the edge of financial ruin and spurred panic selling of cattle in some areas.
The period between 1996 and 1997 was the driest in England and Wales since reliable records began more than 200 years earlier.
During the dry season in Indonesia, much of the country is suffering from water shortages. In cities, trucks, bicycles, motorbikes and people are lined up around the clock at the main water-pumping stations to collect water from the last municipal supply.