As heavy rains lash Mumbai, IMD predicts more

Scientists blame warming of the ocean, poleward shift on the low-level jet stream and anthropogenic (human-led) activities resulting in carbon emissions

New Delhi: As heavy rains lashed Mumbai, the IMD predicted more along the West Coast, Central India, East India, Peninsular parts, Kerala and Karnataka, with scientists attributing the recurrent pattern to “increasing warming of the ocean, pole-ward shift on the low-level jet stream and anthropogenic (human-led) activities resulting in increased carbon emissions.”
Monsoon winds over the Arabian Sea are exhibiting large fluctuations due to a warmer environment. Frequency of low-pressure systems in the Bay of Bengal has declined and extra moisture is transported in from the Arabian Sea, aiding Monsoon winds leading to extreme rain episodes across the entire Central Indian belt.
Such anomalies will become a recurrent pattern with “increasing warming of the ocean and “pole-ward shift on the low-level jet stream” which impacts the Indian summer monsoon.
Warm SSTs over the northern Arabian Sea result in increased moisture and large fluctuations in the monsoon winds. Urbanisation and other land use, as well as aerosols, contribute to the localised heavy rainfall occurrences, scientists say.
Meanwhile, another Low-Pressure Area is likely to develop over the Bay of Bengal around August 9
According to studies, widespread extreme rain events across Central India have tripled since 1950, resulting in large scale floods and catastrophic loss for life and property across Central and Northern India – Gujarat, Maharashtra, Madhya Pradesh, Chhattisgarh, Telangana, Odisha, Jharkhand, Assam and parts of Western Ghats (Goa, north Karnataka and South Kerala)
Frequency of localised heavy rain occurrences over India has increased during 1951–2015. There have been 268 reported flooding events in India between 1950-2015, killing and leaving thousands homeless, they suggest.
Notably, the rise in extreme rainfall events is taking place over a region where total monsoon rainfall is decreasing. The intensification is against the background of a declining monsoon rainfall makes it catastrophic
According to a recent report by Ministry of Earth Sciences, ‘Climate Change Assessment over the Indian Region’, with continued global warming and expected reductions of aerosol concentrations in the future, climate models project an increase in the annual and summer monsoon mean rainfall, as well as the frequency of heavy rain occurrences over most parts of India during the twenty-first century.
As per a 2017 paper in Nature Communications the frequency of low-pressure systems in the Bay of Bengal has declined and this extra moisture is transported in from the Arabian Sea, aiding Monsoon winds leading to extreme rain episodes across the entire Central Indian belt.
Another study by scientists at the New York University claims that a poleward shift in the monsoon low-level jetstream (LLJ), which transports moisture from surrounding oceans to the Indian landmass, has been detected.
Dr Roxy Mathew Koll from the Indian Institute of Tropical Meteorology says: “While it is too early for an in-depth analysis of the ongoing floods, what we can say is that there is an increasing trend in heavy rainfall events on the west coast of India.
“In our analysis of rainfall data over the last 70 years, we find a three-fold rise in extreme rains along the west coast and central India. This is because the monsoon winds over the Arabian Sea are now exhibiting large fluctuations, thanks to a warmer environment.
“Occasional surges in the winds drive a huge amount of moisture supply from the Arabian Sea, across the entire west coast. These episodes result in an intense rainfall spread over three days.
“Besides some of my colleagues at New York University have found a slight northward shift of the monsoon westerlies in recent decades, this could mean that the chances of heavy rainfall might be larger towards the north of Western Ghats— but that aspect is yet to be explored.”
Dr Anjal Prakash, IPCC’s Lead Author on chapters on urbanisation and mountains, adds: “Some of the Indian cities such as Mumbai, Kolkata, Vizag and Goa are at greater risks due to its proximities to the sea or being in the high-hazard zones.
“Mumbai being the richest Indian Municipalities do not have lack of resources to adapt to these climatic events. With proper adaptation measures, some of the impacts of high rainfalls could be avoided”
Quoting recommendation of the Madhav Chitale committee, Anjal Prakash says the Mithi River which is the major drainage point in the north has been reduced to an open drain due to severe encroachments and discharge of industrial effluents into the river and its mangrove forests need to be protected by bringing special legislation.