Droughts

Historically, droughts affect more people than a heat wave. Not only are there the high temperatures and lack of precipitation, but also the agricultural, economic, and sociopolitical impact on inhabitants within the affected region, as well as those dependent upon goods and services from that area.

Drought areas tend to be warmer than normal for several reasons. One is that the lack of rain-producing clouds allows more sunshine than normal. The other is that the dry ground and parched vegetation result in little evaporation, allowing most of the sun's energy to be used in warming the air. In turn, the increased temperatures result in lower relative humidity, making it less likely to rain.

Types Of Droughts

• A meteorological drought is any substantial prolonged deficit of rainfall. There is no consensus on what the deficit is or what the time period should be.

Usually, this is determined by the locale. For example, climatologically arid regions are not normally considered to be in drought conditions.

The Palmer Drought Severity Index is a long-term meteorological drought severity index published by the NOAA/USDA Joint Agricultural Weather Facility. There are other indices of drought as monitored by the National Drought Mitigation Center, such as Percent of Normal (Precipitation) and the Crop Moisture Index.

• A second type of drought is the hydrological drought in which there are critically low ground water tables and reduced river and stream flow. In addition to a lack of rain, low wintertime snow accumulation in higher elevations can results in this type of drought in adjacent lowlands during the warm season.
• The third type is an agricultural drought, which is perhaps the one most people associate with extreme heat. This is when extended dry periods and general lack of rainfall results in insufficient moisture in the root zone of the soil. This causes an adverse effect on cultivated vegetation.