The National Drought Mitigation Center conceptually defines drought as “a protracted period of deficient precipitation resulting in extensive damage to crops, resulting in loss of yield”. Three indicators of drought include below normal soil moisture, reduced stream flow, and, most obviously, lack of precipitation. These indicators can be kept track of in order to help mitigate the effects of drought. The U. S. Drought monitor makes maps of the United States that show severity of droughts available to the public (Fig. 1).
Nick Arya in his article, “Write a brief note on the characteristics of Drought”, lists five major characteristics of drought. The first essential characteristic of drought is that it builds over time with an increasing scarcity of water. The second characteristic says that because drought builds over time it does not have a well-defined start. And like the beginning, the end of drought isn’t well-defined either. The end comes gradually, except in extreme cases where a long spell of heavy rainfall causes the end. The fourth characteristic says that drought is either localized or regional, depending on the severity of the drought.
The area affected by the drought is generally an elliptical shape rather than a circular shape. The effects of drought are far reaching, even if the drought itself is localized. In the article “What are the Effects of Drought? ”, Larry West describes some of the lasting effects of drought. One of the more obvious effects of drought is widespread thirst, especially in underdeveloped regions where water is not as readily available as in industrialized countries. Along with a reduction in drinking water, existing stores of drinking water can become contaminated because fresh water is not being introduced to the system.
Contamination of drinking water causes disease to spread through populations. Because drought conditions are due to a lack of precipitation and soil moisture crops and agriculture are also negatively affected. The negative effects on agriculture can cause a decrease in the production of food and cause hunger and famine. Reduced levels of water sources and food sources can stir up conflicts between people and in extreme cases, start battles and wars. The lack of moisture in soil and vegetation alike make for prime conditions for wildfires to occur.
These can be easily started and difficult to put out. This can cause loss of life and property. In extreme cases of prolonged drought, much like the circumstances of the Dust Bowl, migration and relocation of populations becomes common. Figure 1. Most recent map of the United States showing current drought conditions. There are many variables that contribute to drought formation so predicting drought events is difficult. One of the major causes of drought globally is the occurrence of high pressure cells, in which sinking air prevents cloud formation and decreases precipitation (Hanson, 1991).
In the United States ENSO patterns cause above normal precipitation levels in some parts of the country but in other parts of the country temperature levels will rise and drought conditions will occur (NDMC). On the west coast of the United States the displacement of the Polar Front Jet Stream will bring large amounts of precipitation in the winter, but in the summer it can cause severe heat and lack of precipitation and result in drought (NDMC). Figure 2. Representative map of the United States showing areas of high pressure, drought-causing conditions (Hanson, 1991). The effects of climate change that are facing the 21 t century, in terms of drought, are highly variable based on location.
According to the NDMC global precipitation could increase 7-15%, while at the same time global evapotranspiration could increase by 5- 10%. The general pattern is expected to show more precipitation at high latitudes and lower precipitation at the mid to low latitudes. This is significant because in the midcontinent regions, evapotranspiration will be greater than precipitation and drought will occur. Increased temperatures along with decreased precipitation will allow for more persistent, longer lasting droughts.
Juliet Eilperin’s article titled “Climate change means more frequent droughts and floods, UN panel says in report” covers a report issued by the UN Intergovernmental Panel on Climate Change. This report says that climate change will amplify the climate extremes already seen today. This supports the idea that areas already afflicted with drought-sensitive climates are likely to see longer, more intense drought. Because there are so many different models for the future of climate change it is difficult to accurately predict the effects that climate change will have on any one climate event.