We define drought in four general ways--hydrologic drought, meteorological drought, agricultural drought, and socioeconomic drought. Why the different categories? Each represents a different effect. For example, hydrologic drought represents the effects of drought on water availability from groundwater and surface water, including reservoirs. Agricultural drought considers water availability in the soil to support crop growth. Meteorological considers duration of periods from the last amount of precipitation that equaled or exceeded a specific threshold. Finally, socio-economic drought focuses on the economic effects of water shortage. When you look at a drought report issued by the U.S. Department of Agriculture, you see a combination of meteorological, hydrological and agricultural drought assessments. Drought maps indicate the severity of water shortages in terms of last received significant precipitation, soil moisture and surface and groundwater storage.
Drought Intensity for February 18, (from United States Drought Monitor, http://droughtmonitor.unl.edu/Home/StateDroughtMonitor.aspx?NV):
D0 - Abnormally Dry
D1 - Moderate Drought
D2 - Severe Drought
D3 - Extreme Drought
D4 - Exceptional Drought
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