Assessment of Compound Drought and Hot Extreme Conditions Over West Rajasthan, India

Compound extremes characterized by simultaneous or consecutive incidence of multipleextreme events (i.e. dry and hot extremes), or fusion of extreme events amplifying theirindividual impacts, or amalgamation of non-extreme events resulting in an extreme impactwhen combined. Our key focus was on understanding compound extremes, particularly theinteraction between prolonged dry spells and intense heat waves. We explored the individualextremes of drought (dry extreme) and high temperatures (hot extreme) using some essentialindices like SPI, STI, WSDI and CDD. Also to better understand these complex events, weemployed two specialized tool, the Compound Drought and Hot Extreme Index (CDHI) andone of the Joint extreme index (JEI) i.e. WDS (Warm and Dry Spell) for meteorologicalsubdivision-17 i.e. west Rajasthan region. Both CDHI and JEIs are used to characterize thejoint occurrence of extreme precipitation and temperature. In this study, we employedtemperature data from the Indian Meteorological Department (IMD), recorded at a resolutionof 1 degree, covering the years 1951 to 2019. Additionally, we gathered monthlyprecipitation data, which was observed at a finer resolution of 0.25 degrees, spanning from1901 to 2019. Moreover, to seamlessly integrate and refine our analyses, we applied 2Dbilinear interpolation, using Euclidean interpolation principles, to align the 0.25-degreegridded precipitation data with the 1-degree gridded framework of temperature. For instance,the SPI values of -1.77 and -2.28 for the monsoon seasons of 1987 and 2002, respectively,suggests that the meteorological drought in 1987 was less severe than in 2002. Conversely,the STI values indicate that 1987 was hotter than 2002, with STI values of 3.15 and 1.91,respectively. Consequently, comparing Compound dry and hot extremes based solely on SPIand STI data proves challenging. Therefore, CDHI served as a valuable metric for comparingthe overall severity of compound drought and hot extremes. A lower CDHI value indicatesmore severe compound drought and hot extremes, and vice versa. The CDHI values for theyears 1987 and 2002 were -2.91 and -2.51, respectively, suggesting severe compound droughtand hot extremes in 1987. Also, as we plotted the time series plot for the meteorologicalsubdivision 17, i.e., west Rajasthan region, it was observed that when the time periods weretiny (1, 3, or 6 months), the SPI, STI, and CDHI frequently moves above or below zero. Butas the time periods were lengthened or increased (12, 24, 36, or 48 months), the SPI, STI, andCDHI responded dilatorily to changes in precipitation, i.e., overall periods with positive andnegative values of indices reduced, but the ones which appeared were longer in duration.