Rainfall Contribution by Cyclonic Disturbances Over India In Two Epochs During 1901–2021 and Risk Assessment

The peninsular Indian subcontinent bounded by the Bay of Bengal and the Arabian Sea is highly vulnerable to destruction induced by cyclonic disturbances (CDs). Besides the stronger devastating winds generated by the CDs, the torrential rainfall imparts floods and landslides over the places of landfall. To characterize the repercussions owing to the warming climate, trends of rainfall contributions from the CDs (CDR) over India for both the pre-warming (PWP: 1901–1946) and the current warming (CWP: 1947–2021) periods were examined. The CDs considered either crossed or grazed the Indian coastline, and the rainfall within a radius of 5° from the storm center has been considered. The average CDR for PWP is about 60–70 mm/year, while the CWP accounts for over 110 mm/year, with an increasing trend during the pre-monsoon season. The CDR percentage contribution analogous to the seasonal rainfall over India is within 30% for PWP; however, it is nearly 80% for CWP. Additionally, for the post-monsoon season, the average rainfall is <80 mm/year and exceeds 140 mm/year for PWP and CWP, respectively. The variability in percentage contribution is like the pre-monsoon, even though there is an increasing trend for both epochs. Subsequently, the risk induced by the CDR in the coastal states of India is estimated using a statistical approach. The return levels characterize the probable annual maximum CDR via best-fit extreme value theory (EVT) model configuration. The EVT model results exhibit an analogous near-future trend in the eastern coastal states of India, i.e., Odisha, Andhra Pradesh, and Tamil Nadu. The EVT results indicate that these eastern coastal states would exceed the extremely heavy rainfall threshold induced by CDs in <10 years. However, the corresponding timeframe for the western coastal states would be >20 years. Also, the western coastal states of Karnataka, Kerala, and Maharashtra could become prone to excessive hazards induced by extreme CDR in the far future.