The Quantification of Drought: An Evaluation of Drought Indices

Indices for objectively quantifying the severity of meteorological, agricultural, and hydrological forms of drought are discussed. Indices for each drought form are judged according to six weighted evaluation criteria: robustness, tractability, transparency, sophistication, extendability, and dimensionality. The indices considered most promising for succinctly summarizing drought severity are computed for two climate divisions in Oregon for 24 water years, 1976–99. The assessment determined that the most valuable indices for characterizing meteorological, hydrological, and agricultural droughts are rainfall deciles, total water deficit, and computed soil moisture, respectively.