When droughts occur, they can have a number of negative effects. The drought can cause the destruction of plants and animals, and the deaths of vast numbers of human beings. Droughts can be the result of a failure of winter rains and snows. The absence of winter moisture can affect plants, animals, and humans. In many areas, water supplies are dependent upon winter moisture that is stored for use by farmers and cities, and may, if the drought is prolonged, create immense problems for humans. For example, Los Angeles, California, is dependent for much of its water supplies on snowmelt from the snowpack in the high Sierra Mountains in northern California. If there is a winter snow drought, it is a threat, because water supplies have to be managed very carefully and alternative supplies sought.
The failure of the winter snows or rains, the spring rains, or even summer showers to come can also be accompanied by weather patterns that are damaging. Warm winter temperatures may trick plants into blossoming as if the warm seasons of the year have arrived. The sudden return of cold weather can then bring freezing temperatures that damage or kill plants that have emerged from a wintertime dormant state.
Global warming as a likely cause of the destruction of glaciers is of enormous concern to many scientists, the United Nations, and others because their destruction may greatly affect the rivers of India, China, and Southeast Asia. The Himalayan glaciers are the sources for the largest rivers in Asia. The Indus River, especially in its Punjab area, feeds millions. The Ganges and the Brahmaputra are also the sources of water for 500 million Indians. If the Himalayan ice pack were to disappear because of global warming, then the Yellow, Yangtze, Mekong, and Sal-ween rivers would probably disappear or be reduced to only a trickle of their former flow volumes. The effects could be deadly for billions of people.
Droughts are often accompanied by higher than normal temperatures. The higher temperatures cause plants to suffer heat stress. The heat stress from temperatures that may be 10, 20, or more degrees above normally occurring temperatures dry out plants so that not only crops, but also grasses, brushes, trees, and other plants are vulnerable to dehydration. They may become dormant to endure a drought. Diseases may then successfully attack plants that would not have normally been vulnerable.
The longer a drought continues, the drier the vegetation, including dead-fall and the decaying leaf matter on the ground in wooded areas. The possibility of forest fires, or of fires in more open country, begins to grow at an exponential rate. It is not unusual for drought to be accompanied by many forest fires or brush fires.
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