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Why 2022 has been Bengaluru’s wettest year so far

The city had received 1,709 mm of rainfall as of October 20, the highest figure recorded in 121 years

As of October 20, Bengaluru has recorded the highest-ever rainfall in the past 121 years; (Photo: ANI)

By Ajay Sukumaran: Rain-battered Bengaluru surpassed a record this week. Rainfall during 2022 stood at 1,709 mm as of October 20, making it the highest ever annual rainfall figure recorded in 121 years by the city’s meteorological centre. But there are two more months to go before the year closes—and another rainy spell ahead with the North-east monsoon just setting in.

Since end-August, Bengaluru’s rain woes have only compounded. In September, much of the city’s IT corridor in Mahadevapura was flooded, bringing the city’s civic mess into sharp focus and prompting the administration to take up a demolition drive to clear encroachments on storm-water drains. Even as things were hobbling back, a series of heavy downpours through last week—capped by a thunderstorm on October 19—inflicted fresh misery on several localities.

The forecast, however, is that rain will continue for a few more days. According to the meteorological centre, the normal date of onset for the North-east monsoon was October 20. “That is the primary rainy season for Tamil Nadu and adjoining areas. So this kind of rain will continue for a few days,” says Dr Geeta Agnihotri, director of the meteorological centre in Bengaluru.

Low pressure trough

The recent spells of rain have been marked by short torrents. Why is Bengaluru getting such a dunking? Primarily, it’s because of troughs, or low-pressure areas in the atmosphere, which typically stretch along a line or axis as the monsoon withdraws. “Very interestingly, this trough axis is hanging around Bengaluru for many days,” says Prof. G. Bala of the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science (IISc). “It’s not raining in Bengaluru alone.”

Indeed, neighbouring Tumkur district too has been reeling from heavy rain—this includes even its driest parts, such as Pavagada where the country’s largest solar park, spread over 12,000 acres, is situated. Some parts of the park were submerged this week.

Highest rain since 1901

Weather observation at the meteorological centre in Bengaluru began in 1893 at the city’s Bowring Hospital; in 1901, the centre was shifted to its current location on Palace Road. The 1,709 mm of rainfall recorded between January 1 and October 20 this year has been the highest so far in a year, surpassing the previous annual high of 1,696 mm in 2017. Prior to that, the rainiest year was 2005—1,606.8 mm.

While the recent rainfall in Bengaluru has caught everyone off guard, there aren’t discernible patterns to it. “The second highest rainfall was in 2017; the third highest was in 2005, which is a gap of nearly 12 years. So you can’t infer that it has started happening very frequently,” says Agnihotri. “One has to really make an in-depth study as to how and why this is happening.”

Apart from vehicular emissions, does Bengaluru’s urban sprawl affect the intensity of rainfall because densely constructed urban areas are known to trap heat? It is a plausible hypothesis but there are no local-level studies to conclude so, say experts. “This kind of a thing has not been postulated at the city level. People have done studies taking very large-scale data sets,” says Agnihotri. That said, these questions are a hot topic among meteorologists today.

According to Prof. Bala, some of latest simulation models globally have been attempting to quantitatively interpret events such as heavy rainfall in terms of climate change and other factors. “In the US and Europe, scientists use models immediately after an extreme rainfall event and estimate how much of that rainfall is attributable to climate change. This so-called event attribution is done in almost real-time today.”

Rain intensity and groundwater

Despite the misery that Bengaluru’s heavy spells of rain have brought, there’s a positive side too—from the point of view of recharging groundwater aquifers. Given the city’s explosive growth—both in area and population in just over a decade—large parts of the peripheral localities depend on water tankers because the piped-water infrastructure hasn’t kept pace. “Some particular extreme rainfall events can improve the groundwater system very well,” says Prof. M. Sekhar, who researches groundwater hydrology at IISc. For instance, the 2017 rains increased groundwater significantly, he says. “So the recent rains would have raised groundwater levels.”

Again, not just in Bengaluru alone. Given the high rainfall in large parts of southern Karnataka over the past 2-3 years, groundwater levels have gone up significantly in water-starved districts like Kolar, adjacent to Bengaluru.

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