Evolution of Compound Hydro-Climatological Extremes (Droughts and Heatwaves) over India

<p>Extreme hydro-climatological events like floods, droughts, heat waves, cold waves, etc. have become more frequent worldwide, in recent decades. While these extremes severely harm not only a specific society but the entire ecosystem with long-lasting impacts, their simultaneous occurrence may cause even worse harm on a variety of spatial and temporal scales. This thereby necessitates an extended investigation of the ‘Compound events’. Past literature has explored the compound impacts of precipitation and temperature extremes, across the world. In this study, we examine the incidence of droughts and heat waves, individually, as well as their combined effects, by incorporating the possible effect of changes in precipitation spells on drought episodes, i.e., by deploying the recently developed drought index, Standardized Net Precipitation Drought Index (SNEPI).  Heat waves are accounted as instances where the temperature exceeds a threshold (say, 45°C) for longer than three, or six days. We conducted this analysis over the Indian sub-continent, and “Compound Drought-Heatwave” clusters are identified from the individual extreme event clusters. The spatiotemporal extent of the individual and compound occurrences and their temporal evolution are then quantified, along with the regional characteristics. The climatically driest years show an intensified compound impact over Peninsular India (especially over Southern India), presumably as a result of double-digit deficits in the monsoon brought on by La Niña conditions. The findings highlight the rapid transition of severe compound events to extreme ones in certain climatic zones. Furthermore, the significance of the intensity of the compound extremes within the clusters is addressed. This study helps bring valuable insights into the nature of the relationship between the variables involved in compound event occurrences.</p>