Mumbai: At first glance, the city’s record breaking rainfall appears to contradict one of meteorology’s best known rules El Nino years usually weaken the Indian monsoon. Yet Mumbai has witnessed exceptionally heavy spells, raising a question that many residents have been asking how can a city receive such intense rain during an El Nino year?
The short answer is that El Nino influences the seasonal monsoon as a whole, but it does not control every individual rain event. Weather experts say Mumbai’s recent deluge was driven by a combination of local and regional factors, including an early and vigorous monsoon onset, low pressure systems over the Arabian Sea, abundant moisture supply and unusually warm sea surface temperatures that intensified rainfall over the west coast.
El Nino weakens the monsoon but not every strom
El Nino is a natural climate phenomenon marked by warmer than normal sea surface temperatures in the central and eastern Pacific Ocean. Historically, many El Nino years have been associated with below normal monsoon rainfall across India because the phenomenon alters global atmospheric circulation and supresses rain bearing systems over the subcontinent. However, the relationship is far from absolute.
Meteorologists have repeatedly pointed out that while El Nino can influence the overall seasonal rainfall, it does not prevent short lived but extremely intense rainfall episodes. Local weather systems often override the larger climate signal for a few days or even weeks.
Why Mumbai received such heavy rainfall
Several weather ingredients came together at the same time.
An active low pressure system over the Arabian Sea helped draw enormous quantities of moisture towards Maharashtra. At the same time, strong southwesterly monsoon winds continuously transported humid air to the Konkan coast. When these moisture laden winds struck the Western Ghats, they were forced to rise, producing intense orographic rainfall over Mumbai and neighbouring districts.
Scientists have also highlighted the role of warmer than normal Arabian Sea temperatures, which increase evaporation and provide additional moisture for rain bearing clouds. A warmer atmosphere can hold more water vapour, allowing storms to produce heavier rainfall over shorter periods.
Climate change is making extreme rainfall more likely
Climate researchers say another important factor is long term global warming.
While climate change may not directly cause every heavy rainfall event, it increases the likelihood of cloudbursts and high intensity downpours. Instead of rain being spread evenly over several days, cities like Mumbai are increasingly witnessing large volumes of rain falling within a few hours, overwhelming drainage systems and triggering urban flooding.
Monsoon variability is becoming the new normal
Weather experts also note that the historical relationship between El Nino and the Indian monsoon has weakened over recent decades. Other climate drivers such as conditions in the Indian Ocean, especially the Indian Ocean Dipole, regional sea surface temperatures and intra seasonal weather oscillations can either amplify or offset El Nino’s influence. As a result, India can experience normal or even locally excessive rainfall despite an El Nino background.
What it means for Mumbai
For Mumbai, the lesson is clear an El Nino year does not guarantee fewer rain related disruptions. Even if seasonal rainfall ends up near normal or below normal across the country, the city can still witness extremely intense rainfall episodes capable of causing flooding, transport disruptions and infrastructure stress.
Meteorologists say urban centres along India’s west coast are likely to face greater rainfall variability in the future, with longer dry spells punctuated by short periods of exceptionally heavy rain. That makes forecasting individual weather systems and improving urban drainage just as important as tracking broader climate patterns like El Nino.
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