Trends and behaviour of meteorological drought (1901-2008) over Indian region using standardized precipitation-evapotranspiration index

Monthly gridded (0.5 degrees x0.5 degrees) standardized precipitation-evapotranspiration index (SPEI) data of 1901-2008 were used to detect spatial pattern of temporal trend in meteorological drought during the Indian summer monsoon period. The SPEI data were converted into drought duration, magnitude and types of occurrence to capture overall drought scenario. A non-parametric (Mann-Kendall test) method was used to test for monotonic trend at each grid level, whereas the magnitude was estimated using Sen's method. Further, a field significance test was performed at major meteorological regions level to assess whether the individual trends identified could occur by chance in an analysis of large number of time series analysed. Significant (=0.05) increasing trend of both drought duration and magnitude during the monsoon was found over parts of eastern, central and north-eastern region of India, whereas the parts of west coast, arid western region and north India showed significantly decreasing trend. The trends in mid- as well as late-season drought were contributing towards significant increase in drought condition, whereas trends in early-season drought were responsible for decrease in drought events. The time series analysis of rainfall and potential evapotranspiration (PET) illustrated that over eastern part of India the increase in drought was attributed due to decrease in rainfall, whereas the decrease in drought occurrence over western arid region was mainly because of decrease in PET.