Climate Change, Not Just Super El Nino, Drive Mumbai’s Extreme Rainfall: Analysis

Climate change has become the key driver for Mumbai’s extreme rainfall and is a reminder of how climate change is altering Indian monsoon. A warmer atmosphere and rapidly heating ocean is making rainfall events shorter with intense downpours, which is overwhelming the country’s urban infrastructure, according to a new analysis by Climate Trends. 

The analysis pointed out that while a strengthening Super El Niño delayed the onset of the Southwest Monsoon, leaving India with a 40% rainfall deficit by the end of June. However, rainfall intensified sharply as the monsoon entered an active phase, reducing the national rainfall deficit to 20% by July 6 while triggering widespread flooding across Mumbai and the country's west coast.

Climate Change is Reshaping the Monsoon

Experts said the dramatic turnaround illustrated that while El Niño continues to influence when the monsoon arrives, climate change is increasingly determining how it behaves. 

Mumbai witnessed four spells of triple digit rainfall during the first week of July. Between July 1 and 7, the India Meteorological Department's Colaba observatory recorded 791 mm of rainfall, surpassing its normal rainfall for the entire month of July, while the Santa Cruz observatory received 879 mm, almost matching its monthly average.

Dr Raghu Murtugudde, Climate Scientist, Emeritus Professor, University of Maryland and Retired Professor, IIT-Mumbai, said, “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.” 

Arabian Sea Warming is Amplifying the Rainfall 

The analysis said 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. In other words, El Niño is delaying the rains; climate change is intensifying them.

Citing a study by Nature, analysis said moisture supply for the summer monsoon rainfall along the west coast of the Indian subcontinent is mainly transported from the Arabian Sea. The Middle East warming is almost two times faster than other inhabited parts of the world and has been causing a dramatic increase in atmospheric instability in the Arabian Sea by thrusting moisture supplies northward. Consequently, the regions of Northwest India have been vulnerable to unprecedented rainfall. The land heating across the Middle East has been responsible for 46% of the intensified rainfall over Northwest India and Pakistan during 1979–2022.

Long-term rainfall data also pointed to a growing trend. Average monsoon rainfall in Mumbai increased by nearly 15% between 2001 and 2024 compared with the 1981–2000 period, while Pune recorded a 23% increase over the same period, according to data cited in the report. 

Climate projections suggested the trend could intensify further. Coastal Maharashtra, including suburban Mumbai, is projected to experience almost an additional week of heavy rainfall during the southwest monsoon. 

Urban Planning is Worsening Flood Risks

Experts cautioned that rainfall alone does not determine flood risk. Urbanisation, the shrinking of natural drainage channels, concretisation, and inadequate drainage infrastructure have significantly increased Mumbai's vulnerability to flooding. 

Vishwas Chitale, Fellow at the Council on Energy, Environment and Water (CEEW), said Indian cities need to strengthen flood preparedness through early warning systems, risk mitigation measures and year-round resilience planning.

"Various cities in India are in the process of developing climate action plans, which must focus on building year-round resilience," he said.