Abstract

Here we propose a new methodology for calculating the Standardized Evapotranspiration Deficit Index (SEDI) at the global scale using the difference between the actual evapotranspiration (ET) and the atmospheric evaporative demand (AED). ET was estimated by the Global Land Evaporation Amsterdam Model (GLEAM) v3a. The SEDI has been proposed recently to quantify drought severity based on the difference between actual evapotranspiration (ET) and the atmospheric evaporative demand (AED). Our findings demonstrate that, regardless of the AED dataset used for calculations, a log-logistic distribution is needed in order to fit the ED time series. As such, in many regions worldwide, the SEDI is insensitive to the AED method used for calculation. The SEDI showed significant correlations with the Standardized Precipitation Evapotranspiration Index (SPEI) across a wide range of regions, particularly for short SPEI time-scales. Overall, while this work provides a robust approach for calculating spatially and temporally comparable SEDI estimates, regardless of the climate region and land surface conditions, further studies remain needed to assess the performance and the applicability of the SEDI to quantify drought severity across varying crop and natural vegetation areas.

Highlights

  • Different studies have demonstrated the importance of the atmospheric evaporative demand (AED) in triggering drought or intensifying drought severity [1,2]

  • The log-normal and Weibull distributions showed a markedly high percentage of series with no solution for the Standardized Evapotranspiration Deficit Index (SEDI) suggesting that they are least suited for SEDI calculation, so they were removed from further analyses

  • After testing eight different candidate probability distributions, we found that the log-logistic distribution showed clear advantages for calculating the SEDI

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Summary

Introduction

Different studies have demonstrated the importance of the atmospheric evaporative demand (AED) in triggering drought or intensifying drought severity [1,2]. For these reasons, several drought indices use the AED in their formulations. Drought indices based only on AED have been recently formulated under the premise that AED anomalies are strongly connected with precipitation, soil moisture and actual evapotranspiration (ET) anomalies [4,5]. Kim and Rhee [6] proposed the Standardized Evapotranspiration Deficit Index (SEDI) using ET data estimated based on the Bouchet hypothesis. We follow the same nomenclature to refer to a standardized drought index based on the ED.

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