1/ With climate change, the storyline has changed for Mumbai and the coastline of India. This thread discusses how storms surge from intense cyclones, heavy rains, and sea-level rise are all overlapping—to create prolonged large-scale floods.
#MumbaiMustPrepare @MumbaisMagic Image: Liam Reading, American Geophysical Union (AGU)/Eos.
2/ Arabian Sea is brewing more intense cyclones than ever. Tauktae was the most intense cyclone (220 km/hr) that came very close to Mumbai. Cyclones drive storm surges—huge waves (5 m high) that push water onto the land, flooding the coast.
◉ Flood = storm surge
3/ Cyclones are bringing more rains than ever. Global warming has made more water available as warm air holds more moisture. Tauktae brought heavy rains of 230 mm in a day (SantaCruz, Mumbai), an all-time record for May.
◉ Flood = storm surge + rain water.
4/ Sea level rise is at a fast pace along the coast of Mumbai, at about 3 cm per decade now. This may be 5 cm in the coming decades, which means half a meter underwater in a century.
◉ Flood = storm surge + rain water + sea level rise.
5/ These floods occasionally ride on a high tide, compounding the impact and prolonging the floods inland. This happened with Cyclone Yaas on Odisha coast, despite it being a moderately severe cyclone (120 km/hr).
◉ Flood = storm surge + rain water + sea level rise + high tide.
6/ We always forget to add that the coastal population is increasing. Increasing exposure due to the rising population is one of the most important causes for losses due to increased vulnerability to climate change.
Mumbai population = 21 Million in 2021 and 42 million in 2050.
7/ As cyclone season gets over, Mumbai should get ready for heavy rains. Our research shows a threefold rise in widespread extreme rains that cause largescale floods, not only along the west coast but also central and north/east parts of India.
8/ Unequal scenes.
Where are the rivers, flood plains, and mangroves that should be absorbing the Mumbai floods? As strong winds, rains, and floods lash out, will it be those shacks that get flooded first or will it be their blue tarpaulin roofs that get blown away? Image: Johnny Miller, Unequal Scenes.
9/ Improved monitoring, forecasts and disaster management have brought down the number of deaths. But climate change has brought new challenges with rapidly intensifying cyclones and overlapping floods. Need to further improve our monitoring & forecasting
10/ We can’t wait for forecasts every time for evacuating people. We cannot evacuate houses, cars, infrastructure, and ecosystems. Cyclones, heavy rains, sea level, and overlapping floods are projected to intensify along the west coast in response to continuing carbon emissions.
11/ What we need to do first is a risk assessment that can demarcate the regions where the risks of floods, cyclones, and severe weather events are largest. Based on that, we need to disaster-proof these regions, using both natural and artificial defenses, and other methods.
12/ Bring back the mangroves. Mangroves act as the sponge of the city, breaking the flow of flash floods and absorbing the impact. Mumbai lost a lot of its mangrove cover and freshwater drainages, and we need to recover them. BKC was built over hectares of mangroves. Image: IPCC SROCC Report, SLR = sea level rise.

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1 Jun
IMD's seasonal forecast today indicates normal monsoon rainfall this year. This image shows how important are the oceans for the monsoon—and ocean observations for monsoon forecasts. The tentacles of the Indian, Atlantic, and Pacific oceans have a tight grip on the monsoon.
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150 Years of All India Summer Monsoon Rainfall.

Count the drought and wet years during the last 20 years. When was the last time that we got a wet year?

Data Source: IMD. Compiled by IITM.

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Reference: nature.com/articles/ncomm…

The decline in total rainfall coincides with an increase in heavy rains across many parts of India—denoted by the yellow-red colors.
Reference: nature.com/articles/s4146…

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13 May
Cyclone along the India-Pakistan border. IMD/global forecasts indicate that the low-pressure system in the Arabian Sea will develop into Cyclone #Tauktae on 16 May, move close to the west coast, and advance to the Indo-Pak north of Gujarat. Heavy rains expected along the track.
IMD weather forecast bulletins are available here:
INCOIS-IMD joint bulletins are available here:
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