A drought means different things to different people. Technically, a drought is a period of abnormally dry weather sufficiently long enough in a given area to cause a shortage of water, whether it is for crops, recreation, water supply utilities or other purposes. As you can imagine, a drought for someone who lives in a desert region would be very different than for a person living among Wisconsin’s many lakes.
There are several definitions of drought, but in general there are three types. A meteorological drought is any substantial and prolonged lack of rainfall over a period of time in a given region. A hydrological drought is a deficiency in surface or subsurface water supplies. An agriculture drought exists when there is not enough soil moisture to meet the needs of a crop at a particular time.
Because there are different types of droughts, there are different methods of measuring the severity of a drought. For example, a meteorological drought can be defined in terms of the percent deviation from the normal precipitation in the region, while a hydrological drought is defined in terms of stream flow, lake levels and groundwater levels.
An effective measure of the impact of drought on agriculture is the Palmer Drought Severity Index. This index, developed in the 1960s, is based on the supply and demand of a water balance equation. It takes into account the precipitation deficit of a location, the temperature of the region and the locally available water content of the soil.
Currently, the Palmer Drought Severity Index lists southern Wisconsin as having “severe drought” conditions, though conditions are improving with the recent rains.