Increased frequency of urban floodings in coastal Indian cities caused by variation in monsoon rainfall: Influencing factors, challenges, and solutions

Coastal cities in India houses nearly 100 million people and are evenly distributed across India’s 7516-kilometer coastline. These cities are important centers of socio-economic activities in the country and are some of the densely populated regions in the world. A number of studies recently have predicted that there is a risk of substantial portions of these cities’ areas being lost to the sea due to sea-level rise in the next few decades, since a major portion of these cities are at a near zero elevation from the mean sea level (M.S.L). Further, in the past few decades, major coastal cities in India have been repeatedly affected by recurrent extreme rainfall events and subsequent floodings. Several studies document that rapid change in the Indian monsoon, increased frequency in the formation of cyclones and the swift changes in the hydro-climatic regime in the Indian Ocean are the major contributors to the occurrence of these extreme precipitations events. While we can safely conclude that these events are likely to occur more frequently in the future, it is important to understand the factors that control and influence these events, comprehend how the cities are and will be affected, and develop feasible policy changes and mitigation action for effective governance. In this paper, we have taken the case of Chennai – an important coastal city located in the southern part of India that has been severely affected by extreme precipitation and subsequent flooding (notably the infamous 2015 Chennai floods) in the past few years, to study the influencing factors contributing to these events and the ground challenges faced by the government machinery in planning and managing these disasters effectively. Our findings indicate that there is a notable variation in the monsoon rainfall pattern in Chennai and the net annual rainfall in the city has increased significantly in the past decade (by ~15%). Further, we found that significant urban centers in the city, especially the regions that are at near zero elevation (± 5 meters above M.S.L) are more vulnerable to flooding, and the important contributing factors to the increased severity of the recent floodings include the lack of adequate stormwater drainage infrastructure and poor policy choice of converting natural surface water bodies (lakes and ponds) into towns during the past three to four decades. We also discuss the planning and execution of Chennai city’s mitigation action during the 2021 floods, analyze its success and shortcomings, and suggest sustainable and feasible policy changes and measures that can be adopted for better management of similar events in the future in other coastal cities as well.