Drought looks different based on where and when it occurs, how long it lasts, and whom it affects, which is why drought experts often say, “all droughts are local.” These reasons help explain why no single accepted definition of drought exists. In the most general sense, drought can be defined as an extended period of time when the water availability is less than expected, resulting in supply shortages for some activity or group. Shortages can occur due to changes in the amount of rain or snow that has fallen, shifts in its timing relative to the need, or increased evaporation caused by high temperatures.
Because drought’s definition includes a demand component, drought means different things to different people. In fact, scientists have found more than 150 published definitions of drought. To simplify discussions, drought definitions are frequently classified into five perspectives – meteorological, agricultural, hydrologic, ecological, and socio-economic drought.
Once you move beyond generalizations, drought quickly becomes complex. Its unique characteristics create challenges for planners that differ from other hazards such as tornadoes or hurricanes.