Investigation of Potential Evapotranspiration’s Effect on the Drought Index with Various Regions and Climate Conditions

Drought is commonly defined as a period when a low amount of hydrological variables predominate at a region. In this study, we investigate whether potential evapotranspiration (PET) affects a drought index (SPEI) to assess drought phenomenon at East Asia, Europe, the United States, and West Africa. We focus on various climate zones including arid, semiarid, subhumid, and humid zones for the analysis. The pattern of water deficits and spatial trend of the SPEI are examined to understand drought. Moreover, the area ratio of spatial extent and temporal trend (1951-2010) are analyzed to provide an understanding of features of drought. Two datasets such as the Climate Research Unit (CRU) and the National Centers for Environmental Prediction (NCEP) are used for the study. To calculate PET, we apply for the Thornthwaite equation (TH) and the Penman–Monteith equation (PM). The result of water deficit shows negative values in the arid and semiarid zones of most regions, whereas the opposite phenomenon is observed in the subhumid and humid zones. The result of the spatial trend based on the SPEI represents a clearly decreasing trend in East Asia and West Africa. The result of the area ratio of the spatial extent seems to present large values of neutral or decreasing trend in East Asia and Europe. Also, it shows large values of neutral or increasing trend in the United States, and large values of a decreasing trend in West Africa. The area ratio have different results depending on the different climate zones. The temporal trend based on the spatial extent mostly shows no trend or an increasing trend in the study regions.