Mapping Compound Hazard Potential of Tropical Cyclone and Anomalous Heat in Eastern Coast of India

Compound hazards, such as the sequential occurrence of Tropical Cyclones (TC) and humid heatwaves in close succession, are more destructive than individual and isolated occurrences of each hazard. While landfalling TCs cause catastrophic consequences from storm surges, strong winds, heavy rain, and pluvial flooding, they are often compounded by anomalous heat. The TC-heat joint occurrence raises significant concerns for public health and critical infrastructure, particularly since powerful TCs may lead to major power outages. For example, TC Remal in May 2024 damaged the coastlines of India and Bangladesh, bordering the Bay of Bengal (BoB), impacting > 10 million people without access to electricity and shelter, with an estimated damage totaling $600 million. For the eastern coast of India, with many small to large port cities, including two major urban agglomerates, Kolkata and Chennai, with populations > 10 million, the likelihood of TC-heat joint occurrence has not been assessed so far. We analyze 251 landfalling TCs on the eastern coast of India between 1982 and 2023. We show that ~16% of terrestrial humid heatwave peaks are compounded by the landfalling TCs, and ~8% of moist heat follows TCs. Further, we show the relative increase in peak wet-bulb temperature in TC-compounded heatwaves is as high as around 7−10% in pre-monsoon (April−May) and post-monsoon (October−December) seasons compared to heatwaves not compounded by the TCs. An anomalous rise in TC-compounded heatwave peaks is more pronounced and often exceeds terrestrial heatwave peaks during the post-monsoon season. Although the annual counts of landfalling TCs over BoB show a decreasing trend, our observational analysis of precursor coincidence rate confirms the increased likelihood of TC-compounded humid heat stress, preconditioned by strong to severe marine heat waves. The derived insights highlight a need to prepare adaptation planning for unprecedented compound tropical cyclones and extreme heat hazards when such sequential hazards are expected to occur more frequently in a warming climate.