City’s July rain is highest in 76 years

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Published on Jul 28, 2020 11:34 PM IST
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ByBadri Chatterjee, Mumbai

After surpassing its July average (840mm) within the first 15 days of the month, the city broke its all-time record for July rainfall on Tuesday. The rain tally between July 1 and July 28 (8.30pm) was 1,474.4mm, which is the highest in 76 years. Previously, 2014 had been the wettest July with 1,468.5mm rain.

On Tuesday, south Mumbai recorded intermittent intense spells through the day, with 87.6 mm (heavy) rain from 8.30am to 8.30pm while the suburbs recorded 7.8 mm rain. A yellow alert (heavy rain) has been issued for Wednesday and Saturday by the weather bureau.

Between July 1 and Tuesday, Mumbai has recorded 1,474.4mm rain, which is an all-time record. The India Meteorological Department (IMD) maintains rain data from 1944 onwards, when the Santacruz observatory was established. Though Mumbai had received a record 944.2mm rain over 24 hours in July 2005, when there were floods in the city, the monthly total was 1454.5 mm. Last year, the city recorded 1,464.8 mm rain in July. Other landmark years include 1965 (1,455.5 mm), 1961 (1,385.5 mm), 2011 (1,312.9mm), 2010 (1,250.4mm) and 1988 (1,226.1mm) in 1988.

This month, Mumbai has recorded 75.5% excess rain and witnessed eight days of heavy to very heavy rain. Apart from July 2, the city has received rainfall every day of the month, with five days of very heavy rain. Maximum rain was recorded between July 4 and July 5 (200.8 mm) followed by 191.2mm between July 15-16.

IMD classifies 15.6-64.4mm in 24 hours as moderate rain; 64.5-115.5mm rain as heavy; 115.6-204.4mm as very heavy; and over 204.5mm as extremely heavy rain. IMD officials said rain during July was consistent as opposed to June, when there was a rain deficit with the city falling 98mm short of its rain target and recording the lowest monthly rainfall in five years.

“Weather systems in the Arabian Sea and larger factors such as a weak positive Indian Ocean dipole (IOD) – an ocean-atmosphere phenomenon with difference in sea surface temperatures characterised by cooling in parts of the Indian Ocean, leading to enhanced rain – ensured active monsoon conditions through most of the month,” said an IMD official.

Professor Sridhar Balasubramanian, department of mechanical engineering and IDP Climate Studies, Indian Institute of Technology, Bombay, said, “Positive IOD indicates a warm pool of water in the west Arabian Sea (near Somalia). This is good for bringing moisture over to the west coast.”

However, showers have evaded catchment areas. “Since catchment areas are located further interior from the coast, cloud bands have not penetrated owing to weak wind drag. However, this is likely to change in August as the Bay of Bengal gets ready to churn a system,” said Balasubramanian, adding that the city could expect “above normal” rain in August.

Mumbai has received 82.6% of its seasonal average rainfall from June 1 to July 28.

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