Despite delayed start, city gets 62% of season’s rain in less than a month

The city has also surpassed its average rainfall for July, according to data from the India Meteorological Department (IMD). In 21 days this month, Santacruz received 938mm of rain, as opposed to the monthly normal of 855.7mm

Mumbai: Since the rains finally hit the city on June 25, after a delayed start, the city has already received 62% of its total monsoon quota. While the annual quota is 2,318.8 mm, the city’s base weather station in Santacruz has already recorded 1,458mm of rain since June 1. The majority of these rains were received only after the monsoon’s inordinately delayed onset on June 25. In comparison, between June and September last year, the city received 2,658.3mm of rain at Santacruz.

Earlier this season, Mumbai had also received 90% of June’s average rainfall in just five days, when Santacruz saw 485mm between June 24 and June 29. This phenomenon -- of large rainfall deficits being made up in days -- conforms to changing trends in city’s recent weather data. (Vijay Bate/HT Photo)

The city has also surpassed its average rainfall for July, according to data from the India Meteorological Department (IMD). In 21 days this month, Santacruz received 938mm of rain, as opposed to the monthly normal of 855.7mm.

“If showers keep up at this rate, we will likely surpass the seasonal normal this year as well. However, it is still too early to predict what the rainfall situation will be like in August and September. What’s notable this year is that we had barely any precipitation in the month of June, but we still managed to make up the monthly normal amount for both June and July,” said an official with the IMD’s regional forecasting centre in Mumbai.

Earlier this season, Mumbai had also received 90% of June’s average rainfall in just five days, when Santacruz saw 485mm between June 24 and June 29. This phenomenon -- of large rainfall deficits being made up in days -- conforms to changing trends in city’s recent weather data.

Earlier this year, Hindustan Times had reported on a study published in the international journal, Theoretical and Applied Climatology, which showed a sharp increase in the frequency of heavy (more than 120 mm/day) and extreme heavy (more than 250 mm/day) rainfall events amid intermittent dry spells, instead of moderately intense showers spread out uniformly across the monsoon. This trend became pronounced over Santacruz from the year 1994 onward.

The study also showed that the intensity of monsoon rainfall — between June to September — in Mumbai city and suburbs is also intensifying at the rate of approximately 5.18mm per year, while the intensity of annual rainfall is increasing by about 22mm per year. This is based on IMD data between 1985 and 2020.

These changing patterns are also highlighted in the BMC’s Mumbai climate action plan (MCAP), which warns of the need to urgently improve the city’s flood resilience to combat changing patterns in rainfall. Based on daily rainfall timeseries data from 37 stations over the last 10 years, Mumbai experiences, on average, six heavy (64.5 – 115.5mm), five very heavy (115.6 – 204.4 mm), and four extremely heavy (> 204.5 mm) rain events per year.

Each year, around 9.5%, 8.7%, and 5.8% of all monsoon rainfall is classified as heavy, very heavy, and extremely heavy, respectively, the MCAP states. Recently, “The four-year period between 2017 and 2020 has seen a steady increase in the extremely heavy rainfall events,” the MCAP autions.