City crosses average annual rainfall mark; month of monsoon left

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The city on Sunday surpassed its annual average rainfall of 2,514mm, despite a dry spell in the past two weeks. Mumbai has received 2,527.5mm rainfall from June 1 – the official monsoon onset date – to August 25, with still a month left for the season to end on September 30.

Mumbai had not crossed the annual average rainfall mark last year, with 2,239.6mm rain from June to September. In 2017, however, the city had recorded 2,946.3mm rain in the entire season.

The southwest monsoon officially arrived late on June 25 this year, but Mumbai witnessed three spells of “extremely heavy rainfall” on July 1-2, July 26-27 and August 3-4 when the city received 375.2mm, 219.2mm and 204mm of rain in 24 hours, respectively.

According to Indian Meteorological Department (IMD), from June 1 to August 25, Mumbai suburbs recorded an excess rainfall of 41%, while south Mumbai received 11% excess rain. The entire Maharashtra recorded an excess 22% rain during the same period.

“Enhanced rain activity over short periods, especially during July and early August, helped cover the deficit for Mumbai and surrounding areas that led to sufficient water stock,” said Mrutyunjay Mohapatra, director general, Indian Meteorological Department (IMD). “Extreme rainfall events are becoming an established fact and a trend is being recognised. But since monsoon is highly variable and a dynamic system, we should not compare one monsoon season to another.”

Independent experts said that the rainfall is expected to be subdued till the season ends.

“Revival of rainfall is expected in Mumbai towards August-end but mostly showers will remain light. Similar conditions are expected to continue in the first week of September with intermittent rainfall,” said Akshay Deoras, independent meteorologist and PhD researcher, University of Reading, UK. “Mumbai has witnessed a skewed rainfall pattern this year, like it did in 2018.”

“Most of the rainfall activity was observed in July owing to a combination of low pressure systems coming from the Bay of Bengal, offshore trough and a few weather systems developing over the Arabian Sea. In August, rainfall was subdued as this weather combination was absent,” said Deoras.

Sridhar Balasubramanian, associate professor, department of mechanical engineering and associate faculty, IDP Climate Studies, IIT- B said, “Amid weak El Niño conditions, a positive Indian Ocean Dipole (IOD) – an ocean-atmosphere phenomenon with difference in sea surface temperatures characterised by cooling in parts of Indian Ocean leading to enhanced rain – helped enhance rainfall activity through July and early August. In September, another 250mm rain is expected with monsoon withdrawal expected around September 28-29.”

Private weather forecasting agency Skymet said while the monsoon surge was currently weak, increase in rain activity was expected between August 28 and 30. “Isolated moderate showers can be expected. Multiple spells of exceptionally heavy rain for Mumbai and Konkan coast under the impacts of climate change helped the city surpass its annual average,” said Mahesh Palawat, vice-president (meteorology and climate change), Skymet.