Climate change altering behaviour of Indian monsoon: Experts

El Niño, the recurrent weather pattern that drives up global temperatures, and climate change cannot be viewed independently, as one is delaying the rains and the other intensifying them, according to climate experts.

A rapidly strengthening El Niño in the Pacific delayed the onset of the monsoon and kept rainfall subdued through June, leaving India with a 40 per cent rainfall deficit by the end of the month. Yet, within days, the scenario changed dramatically. As the monsoon entered an active phase by the end of June, Mumbai and large parts of India’s West Coast were battered by exceptionally intense rainfall.

Experts say the new reality is that climate change is fundamentally altering the behaviour of the Indian monsoon.

“Monsoon is presently in an active phase, with several weather systems prevailing across the country. There was a depression over Odisha and a cyclonic circulation over Maharashtra, keeping the western and eastern arms of the monsoon active,” said Mahesh Palawat, Vice President - Meteorology and Climate Change, Skymet Weather.

“Along with this, continuous moisture feed from the Arabian Sea led to continuous regeneration of clouds over Maharashtra in the last three to four days, leading to heavy rainfall,” Palawat said.

Raghu Murtugudde, Emeritus Professor, University of Maryland and retired professor, IIT-Mumbai, explained that Mumbai saw a delayed onset of monsoon, which is partly explainable by El Nino.

“But the global warming pattern of warm Western Asia and shifted Arabian Sea winds have kicked in as expected. Lots of winds as well, which is part of the larger heavy rain over the core monsoon zone. Arabian Sea and the Bay of Bengal are both feeding heavy rain in the interior. El Niño just cannot be separated from global warming anymore.

“Both the Arabian Sea and the Bay of Bengal are active, and a low-pressure system is also starting from the Bay of Bengal. When this happens, and both sides fire up, the core monsoon zone gets heavy rain and that moisture supply also goes over Mumbai. Western Ghats force air to climb, so Mumbai gets lots of rain,” Murtugudde said.

While three-digit rainfall in Mumbai and places along the West Coast are common during the monsoon season, meteorologists suggest that there has been a significant rise in such deluge-like spells during July and August across Maharashtra, Gujarat, South Rajasthan and Southwest Madhya Pradesh.

Scientists emphasise that El Niño and climate change can no longer be viewed independently.

While El Niño influences monsoon circulation and often reduces the number of rainy days, record warming of the Arabian Sea and changing atmospheric circulation are increasing moisture availability, allowing weather systems to produce much heavier rainfall once conditions become favourable.

“El Niño is delaying the rains while climate change is intensifying them. Monsoon dynamics have changed over the last few years, which can be directly linked with climate change. Weather systems forming in the Bay of Bengal have been travelling in a westerly direction, instead of a northwest.

“Additionally, there has been a rise in the moisture loading from the Arabian Sea due to the record-setting ocean warming. This leads to continuous regeneration of clouds over the region in the presence of a weather system,” Palawat said.

KJ Ramesh, Former Director General India Meteorological Department, explained that during El Niño years, the number of rainy days is less.

“But we know that the character of the monsoon has changed forever due to global warming. Rains will be in the form of short duration and high intensity, whether there is an El Niño or no El Niño. Climate change-induced anomalies can be witnessed in how rainfall patterns have changed across northwestern parts of the country.

“These days we see ample rains across Rajasthan, Gujarat and West Madhya Pradesh due to Western Disturbances and their allied systems. We all know that these Western Disturbances are not able to drive the rainfall alone in these regions, but an increased moisture feed from the Arabian Sea has changed rainfall patterns across these areas,” he said.