Dear Tom,
I live near San Diego and we are in a drought, but what constitutes a drought?
— Will Redell
Dear Will,
A drought has no single definition. Its onset depends on the geographic location, even economic conditions. A municipality dependent for its drinking water on a reservoir might well assign a water level below which it deems a drought is underway. A very low rain total in a back yard might suggest that at least a “lawn drought” is underway at that location. The Palmer Drought Severity Index measures long-term (months or even years) affects of drought and excessive wetness. The U.S. Drought Monitor measures short-term (weeks or longer) conditions of excessive dryness. Currently, extreme or exceptional drought extends across southern California and also a large area of the Southeast from central Mississippi into the western Carolinas.
