A Comparative Study on Rainfall Contribution by Cyclonic Disturbances over India Concerning Two Epochs During 1901-2021

Abstract

The Indian subcontinent bounded by the Bay of Bengal and the Arabian Sea is highly vulnerable to destructions induced by cyclonic disturbances (CDs). The stronger devastating winds generated by the CDs, and the torrential rainfall imparts floods and landslides over the places of landfall. To characterize the repercussions due to the warming climate, the trends in rainfall contributions from the CDs (CDRF) over India for two epochs, i.e., the pre-warming period (PWP: 1901-1946) and the current warming period (CWP: 1947-2021) was investigated. The CDs considered either crossed or grazed the Indian coastline, and the rainfall within a radius of five degrees from the storm center has been considered as CDRF to exclude non-CD rainfall. Although the intra-annual variability in the frequency of CDs was appreciable, a seasonal comparison approach was adopted for each time frame under consideration. The average accumulated CDRF during PWP exhibits ~50-70 mm/year, while CWP accounts for over 110 mm/year for the pre-monsoon period. The annual average rainfall indicates an increase in both epochs, whereas the annual CD count shows a positive correlation with CDRF during PWP and a negative correlation for CWP. The percentage contribution of CDRF analogous to the annual rainfall is within 50% during the first epoch, while it exceeds 80% over CWP. A notable increase with a relatively lower contribution and an obscure decline with higher contributions are observed for PWP and CWP, respectively when yearly variability is taken into consideration. For the post-monsoon season, the annual average rainfall is < 100 mm/year and > 140 mm/year, corresponding to PWP and CWP. The annual percentage contribution also follows a similar pattern like pre–monsoon, even though there is an increasing trend for both epochs. The results of the F-test for the annual variability of average CDRF and percentage contribution during the pre-monsoon season are found to be significant at 95% confidence level. Besides, the CDRF is higher over the eastern coastal states, while the annual contributions from CDRF are greater for the state of Gujarat and Rajasthan