Exploring the difference between Standard Precipitation Evapotranspiration Index (SPEI) from in-situ meteorological stations and SPEIbase

Abstract

Drought has destructive impacts on all sectors, such as environmental and agricultural sectors, as well as water resources management. The first step in drought evaluation and monitoring is determining the drought index. Because of its vital role, this research aims to investigate the difference between Standardized Precipitation Evapotranspiration Index (SPEI) at different timescales, 3, 6, 9, and 12-month, based on in-situ meteorological stations and SPEIbase, which is a satellite global product. They were compared in two ways: 1) using drought categorization and 2) drought index (SPEI values). The results showed a significant difference between the results obtained from each dataset. Based on the drought categorization, only 61% of the months were within the same categories. The dominant months were within the normal category (N) because of a wide range ranging between -1 and 1. Furthermore, SPEI values calculated using SPEIbase gave more extreme drought events (ED). However, SPEI using in-situ meteorological stations gave more severe drought events (SD) for all time scales. Also, a significant fluctuation can be noticed based on the difference between SPEI from the two datasets. These results can be attributed to many reasons, such as using different time periods, calculating potential evapotranspiration, and the reliability of the precipitation and potential evapotranspiration.