A new index to assess meteorological drought: the Drought Exceedance Probability Index (DEPI)

Abstract

This paper presents a new index to determine meteorological drought conditions, the Drought Exceedance Probability Index (DEPI), derived from monthly precipitation time series. Its formulation is simple and undemanding in terms of baseline information requirements. This makes the DEPI suitable for routine application to any climate, similar to the well-known Standardized Precipitation Index (SPI). The index is based on the calculation of cumulative rainfall anomalies and their subsequent standardization, similarly to other indices. The hallmarks of the DEPI, and its main comparative advantages, are the process of accumulating anomalies and their standardization process. The paper compares the DEPI with the SPI in several different climates across the world and in all cases the results show the complementarity of both indices. The DEPI shows an excellent ability to reflect the actual severity and duration of droughts, without requiring application on different time scales, unlike the SPI. It is also valid for all types of climates, including arid and semiarid or Mediterranean, for which the literature has shown that using the SPI is problematic.