Climate Change and Extreme Rainfall in Indian Coastal Cities

Which of the following Indian coastal cities may get impacted extremely resulting from climate change?

Mumbai, Panaji, Mangaluru, Kozhikode, Kollam, Nagercoil Chennai, Ongole, Kakinada, Vizag, Brahmapur, Puri & Digha

Which of above Indian coastal cities are more at risk of floods resulting from exposure to multiple flood drivers including extreme high tide, storm surge, extreme rainfall and high river flow?

And, in which of the above coastal cities, compound flood events would occur, upon various flood driving factors coinciding in space and time?

Which of above Indian coastal cities are poised to Jacking Effect of high tide that would possibly prevent urban flooding from being discharged into the sea through the drainage network, and thereby reducing the drainage capacity of the coastal urban drainage network, upon the occurrence of high tides?

Will the impacts of flooding in these low-lying, densely populated, and highly developed cities could remain to be devastating with wide-ranging social, economic and environmental consequences – at any point of time – in the near future – resulting from current climate change?

In the above listed cities, where could we expect the coupled effect of both storm surges and extreme rainfall resulting from climate change – that may possibly lead to (severe) flooding in those coastal areas?

How exactly to go about assessing the spatio-temporal dynamics of the meteorological drivers of compound flooding along those Indian coastal cities?

Whether the concept of Compound Flooding has already been assessed – on a local scale - for ALL of the above coastal cities as a precautionary measure?

Are we in a position to project the likelihood of the joint occurrence of storm surge & extreme rainfall in the above coastal cities individually?

Have we studied the probability of co-occurrence of extremes in meteorological tide and in rainfall in Indian coastal cities that provides insight into large-scale rainfall-driven compound flooding in low-lying coasts and compound flooding in estuaries of small-size and medium-size rivers?

How many of the above Indian coastal cities are in estuarine regions? In those estuarine regions, whether such compound flooding could elevate water levels to a point, where flooding gets initiated?

How many of the above Indian coastal cities are poised to a situation, where, a destructive storm surge already causing widespread water-flooding – even, in the absence of extreme rainfall?

Of course, with an additional extreme rainfall (from climate change), to what extent, in those cities, the flood depth will further get increased and to what extent, the areal extent of the inundated area will further get spreading?

How many of the above Indian coastal cities are poised to a situation, where, a combination of moderate storm surge with an extreme rainfall event would cause flooding?

Have we so far deduced the interdependency between storm surge and extreme rainfall in the above Indian coastal cities as a function of highest annual storm surge, highest daily rainfall, highest annual rainfall & highest storm surge (using copula theory/Kendall’s rank correlation coefficient)?

What kind of variations that have been observed in the dependency between storm surge and extreme rainfall among various Indian coastal cities? How have they altered the flood risk so far? And, how would it alter the flood risk in the future?

Do we have dynamic maps of sea-level pressure and winds towards identifying the prevailing synoptic weather situations that may probably cause compound flooding in ALL Indian coastal cities?

Suresh Kumar Govindarajan, Professor [HAG]

IIT Madras, 22-Dec-2024