On the definition of droughts

In this paper, several considerations for developing a practical, analytical definition of droughts are discussed. These considerations include (1) selection of the nature of the water deficit to be studied (hydrological, meteorological, or agricultural); (2) selection of the averaging period used to discretize a continuous time series (months, seasons, or years); (3) selection of the truncation level used to separate droughts from the remainder of the time series (mean or median); and (4) method of regionalization or standardization. These decisions are discussed in terms of their impacts on various approaches to drought frequency analysis. In this paper, drought events are considered to be composed of duration, magnitude (average water deficiency), and severity (cumulative water deficiency). An application of the proposed drought definition procedure is presented for the case of a frequency analysis of multiyear hydrologic droughts.