Benchmark worst droughts during the summer monsoon in India

Abstract

During the summer monsoon (June-September) season, drought poses challenges for agricultural activities and water availability in India. We develop a framework considering the timing, areal coverage and severity that can be used for the assessment of meteorological droughts as the monsoon season progresses. We estimate the benchmark worst droughts within the monsoon season (June, July, August and September) using the long-term (1901-2020) gridded rainfall. The benchmark worst droughts were identified considering the extent and severity of drought using the Drought Severity Coverage Index (DSCI). The worst meteorological drought in June, July, August and September occurred in 1923, 2002, 1937 and 1907 with a return period of 68, 200, 147, 188 years, respectively. The worst drought in the entire summer monsoon season occurred in 1918, which had a return period of 238 years. The benchmark droughts during June 1923, July 2002 and monsoon 1918 were associated with the warm sea surface temperature over the equatorial Pacific Ocean. The other two droughts (1937 and 1907) were linked with the off-equatorial warming over the Indo-Pacific region. The leading mode of variability in the Standardized Precipitation Index obtained from empirical orthogonal function analysis showed that the western and central parts of the country are most affected by droughts during the summer monsoon season. The second leading mode exhibited declining trends in rainfall with a bipolar spatial variability centred over the Gangetic Plain and southern India. The estimated DSCI for a 2-500 return period can be used for the drought assessment during the monsoon season in India.