This year’s Asian monsoon has been particularly severe. Millions were displaced in China, and up to a third of Bangladesh was flooded as river levels soared.
In Mumbai, the monsoon has turned streets and highways into river rapids, with strong winds toppling trees. Up to 60 percent of the city’s population lives in slums, highly susceptible both to natural disasters, like flooding, and to the coronavirus.
According to meteorological records from the Santacruz Observatory in Mumbai, an astonishing 82.5 inches of rain fell in the city between July 10 and Aug. 7.
Mumbai’s average for the year is about 94 inches. The majority falls during the summer monsoon in June, July and August.
Around the height of the monsoon, extreme rainfall can occur, with rates topping four inches per hour. At least eight days in the past month have brought more than four inches of rain in Mumbai.
In just a 24 hour period between July 15 and July 16, 13.26 inches of rain fell. 40.9 inches came down during a five-day window from July 14 to July 18.
For comparison, average annual rainfall in Washington is 39.7 inches. In Boston, it’s 44 inches, and in Miami, 62 inches.
According to the Indian Express, Mumbai has received more than three-quarters of its typical August rainfall in just the first five days of the month.
The Mumbai Mirror noted on Thursday that the Colaba neighborhood, in the city’s south, reported more than 13 inches of rainfall. That’s its greatest single-day tally since July 5, 1974, when nearly 23 inches fell. At least nine inches fell in just nine hours.
The magnitude of the flooding was blamed on a 140-year-old drainage system, which was designed when the city had much more open space and permeable surfaces to absorb storm water. Those green spaces have been replaced by concrete, according to The Indian Express.
Heavy rains will probably continue for the next few weeks before rapidly diminishing in coverage and intensity into September.
The term “monsoon” describes a seasonal wind shift. During the summer, air over the Plateau of Tibet heats up, as does the atmosphere over the highlands of northern India and into parts of Bangladesh and China. This generates lift and upward motion. As that air rises, it leaves behind a sort of void, or “thermal low,” that draws in moist air from the south, over the Indian Ocean.
That moisture, enhanced by converging onshore winds from the Arabian Sea and the Bay of Bengal, produces remarkably heavy tropical downpours.
In the winter, that mechanism reverses; the oceans prove warmer and generate lift, drawing in dry air from the north and shutting off the rain.
On Wednesday, a photo of a vegetable vendor overcome with emotion while sitting beside a flooded street went viral for capturing the “spirit of Mumbai, tired and beaten,” as one headline put it. By Friday, the equivalent of more than $2,000 had poured in to help Ashok Singh, 45, who was recently forced to pawn his wife’s mangala sutra — or wedding necklace — to purchase food and blood pressure medications for his family. The Mumbai Mirror reported that his daughter will soon be married, as well.
Human-driven global warming is increasing the intensity of the rainfall associated with India’s monsoon. A 2017 study found that the number of extreme rain events in central India tripled between 1950 and 2015. A modeling study conducted in 2019 found that “the frequency of single and multi-day extreme precipitation and flood events are projected to increase substantially in the future over the Indian sub-continental river basins.”