Mumbai Deluge: Of Heavy Rains and Climate Change

With heavy monsoon rains, Mumbai has witnessed a massive flood that has claimed more than 30 lives as of now. Torrential rain started on June 28 and during the past 5 days Mumbai has received very heavy showers. It must be noted that Mumbai had faced a seasonal deficit of rain of about 70% till June 26. But within 6 days the city received so much rain that the city has come to a standstill.

On July 2, Mumbai’s Colaba station recorded 137.8 mm of rainfall whereas the whole of Mumbai received 433.7 mm of rainfall from June 1 to July 1, which means that the city received one-third of its monthly rain in a single day. Similarly on July 1st there was reportedly 92.6 mm rainfall in the city which contributed to total of 230 mm in less than one and a half day. This is 50% of the month’s rainfall in two days.

Mumbai is not alone to have this pattern of rain; Palghar district received 212 mm rainfall on July 1, which is much above the normal rainfall it receives for a day. Others include Raigad, Thane, and suburban Mumbai that received more than 90 mm of rainfall. Notably, this region combined is the small region of western Maharashtra that has received such massive rainfall. With some more districts bearing heavy lashes of rains, most parts of the state of Maharashtra have remained dry.

Can we find a pattern in the rainfall? Yes, there is a pattern and it is an extended dry spell followed by heavy rainfall, so heavy that when it arrives it causes floods, landslides and flash floods. A similar situation had occurred in 2018.

But Mumbai or for that matter India is not the only place to have witnessed a change in its rainfall pattern.

Global rainfall data says that numbers of rainy days are decreasing while intense rainfall (10-15 cm/day) events for a short period are increasing. This suggests that more water is pouring within a short period of time. Data also says that the global precipitation — whether rain, snow or ice — is received within a very short period. The main reason attributable is the man-made climate change where global warming is surging.

The increased intensity of rain with global warming is quite an expected phenomenon because warmer air stores more moisture, and this was predicted by various climate models as well.

Also Read: Global Warming has Made Rainfalls More Intense, but World’s Water Supplies are shrinking.

A study published in Nature in 2017 estimated the extreme rainfall events over central India. The study carried out at the Centre for Climate Change Research, Indian Institute of Tropical Meteorology, Pune, reported that extreme rain events over Central India have increased three-fold in the period between 1950 and 2015. The study also noted a 10-30% increase in rainfall events of more than 150 mm of rain in a day, which has taken place when there monsoon circulation has weakened.

Similar predictions of extreme rainfall events in South and Central India were also made in another study carried out at Indian Institute of Technology, Gandhinagar. Published in Weather and Climate Extremes, the study predicted that India is going to witness extreme rainfall events by mid-21st century due to anthropogenic warming.