Spatio-temporal variation in terminal drought over western India using dryness index derived from long-term MODIS data

Drought has always been one of the major hazards in semi-arid and arid regions of the world. This study was undertaken to investigate spatial trends in terminal drought over western India composed of the states of Rajasthan and Gujarat, which are characterized by semi-arid to arid climate. These two states have always been vulnerable to drought since they receive highly variable moderate to scanty rainfall. Leaf area index (LAI)-based temperature vegetation dryness index (TVDI) for the period 2002–2012 was computed using 8-day composites of Moderate-Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and LAI datasets with 1-km spatial resolution. TVDI maps were prepared for all days of the year (DOY) for the months of September and October, which facilitated our understanding of the spatial extent of drought during different 8-day periods. Based on the analysis, it was found that the LAI-based TVDI could capture drought conditions over space and time. Temporal evolution of the observed crop moisture index (CMI) against TVDI reveals that the TVDI exhibited an increasing trend as the CMI decreased or became negative during the 2002 drought year. A significant and negative relationship (R2=0.23) with TVDI and CMI indicates more sensitivity of TVDI to soil moisture in sparse vegetation canopies under drought conditions. Spatial trends in terminal drought intensity were analyzed using linear regression and Mann–Kendall trend test. It was revealed that a majority of the northern part of the study area witnessed an increase in terminal drought intensity and the southern portion registered negative trends. With 80% confidence, it can be stated that the terminal drought intensity increased at scattered locations over southwestern and central Gujarat. However, over central and southwestern Rajasthan, decreasing trends were registered.