Understanding Hydrological Repartitioning and Shifts in Drought Regimes in Central and South-West Asia Using MODIS Derived Perpendicular Drought Index and TRMM Data

In this paper, we use perpendicular drought indices (PDIs) and precipitation patterns to identify hydrological repartitioning in agricultural regions located in central and south-west Asia over the last decade. The spatio-temporal patterns of surface drought derived from perpendicular drought index (PDI) and modified perpendicular drought index (MPDI) from 250-m MODerate Resolution Imaging Spectroradiometer (MODIS) data in 8-day time steps are compared against two other drought indices: the Standardized Precipitation Index (SPI) as a meteorological drought index and the potential evapotranspiration (ET 0 ) as an agro-meteorological drought index, along with 8-day MODIS Normalized Difference Vegetation Index (NDVI). The coefficient of variation as the ratio of standard deviation over inter-annual mean drought indices, precipitation from Tropical Rainfall Measuring Mission (TRMM) data are employed to analyse trends and shifts of hydrological regimes and its connection to both climate change and anthropogenic activities in the study area. Significant correlations are found between the PDI, the MPDI and precipitation and other applied meteorological and agro-meteorological drought indices. The results show that Central Asia is one of the areas across the globe experiencing dramatic shifts in hydrological regimes, and is being severely impacted by population growth and climate change. While acknowledging previous studies that used the PDI and the MPDI over some study regions in Iran, this paper, however, confirms implementation of higher resolution data (MOD09Q1) in both spatial (250 m) and temporal (8-days) dimensions shows a greater agreement between the drought information extracted by the PDI, MPDI, and field meteorological measurements. Supported by satellite based precipitation observations, we conclude that the perpendicular drought indices can be used as a drought early warning system over arid and semi-arid climatological conditions.