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

Compound extremes characterized by simultaneous or consecutive incidence of multiple
extreme events (i.e. dry and hot extremes), or fusion of extreme events amplifying their
individual impacts, or amalgamation of non-extreme events resulting in an extreme impact
when combined. Our key focus was on understanding compound extremes, particularly the
interaction between prolonged dry spells and intense heat waves. We explored the individual
extremes of drought (dry extreme) and high temperatures (hot extreme) using some essential
indices like SPI, STI, WSDI and CDD. Also to better understand these complex events, we
employed two specialized tool, the Compound Drought and Hot Extreme Index (CDHI) and
one of the Joint extreme index (JEI) i.e. WDS (Warm and Dry Spell) for meteorological
subdivision-17 i.e. west Rajasthan region. Both CDHI and JEIs are used to characterize the
joint occurrence of extreme precipitation and temperature. In this study, we employed
temperature data from the Indian Meteorological Department (IMD), recorded at a resolution
of 1 degree, covering the years 1951 to 2019. Additionally, we gathered monthly
precipitation data, which was observed at a finer resolution of 0.25 degrees, spanning from
1901 to 2019. Moreover, to seamlessly integrate and refine our analyses, we applied 2D
bilinear interpolation, using Euclidean interpolation principles, to align the 0.25-degree
gridded 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 SPI
and STI data proves challenging. Therefore, CDHI served as a valuable metric for comparing
the overall severity of compound drought and hot extremes. A lower CDHI value indicates
more severe compound drought and hot extremes, and vice versa. The CDHI values for the
years 1987 and 2002 were -2.91 and -2.51, respectively, suggesting severe compound drought
and hot extremes in 1987. Also, as we plotted the time series plot for the meteorological
subdivision 17, i.e., west Rajasthan region, it was observed that when the time periods were
tiny (1, 3, or 6 months), the SPI, STI, and CDHI frequently moves above or below zero. But
as the time periods were lengthened or increased (12, 24, 36, or 48 months), the SPI, STI, and
CDHI responded dilatorily to changes in precipitation, i.e., overall periods with positive and
negative values of indices reduced, but the ones which appeared were longer in duration.