Monitoring Agricultural Drought Using the Standardized Effective Precipitation Index

Abstract

Drought is a natural disaster that has always had a severe impact on agriculture, especially rain-fed agriculture. Many studies have indicated that different indices, for example the standardized precipitation index (SPI), do not show acceptable efficiency in quantifying agricultural drought. In the current study, an index was utilized that is the so-called standardized effective precipitation index (SEPI). The SEPI employs effective precipitation during the rain-fed wheat-growing season using a two-layer soil-water balance model. In order to assess the efficiency of SEPI in representing and capturing fluctuations of drought years, SEPI was compared with two SPI time series considering different inputs (annual precipitation and growing season precipitation) during 1981–2008 in seven agro-meteorological stations. The results showed that SEPI had better performance for monitoring variations of the normalized wheat yield time series than two SPI-based indices in different climates. For instance, the maximum compatibility (percentage of captured drought years by agricultural drought indices) between SEPI and normalized yield is related to the Sararoud station, in which the SEPI could capture all seven drought years, while two SPI time series could trap only three years out of seven years.