Inequitable July rain spread leaves several Delhi areas wanting

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[google-translator]

New Delhi: The weather station at Safdarjung, which is representational of Delhi’s weather, recorded surplus rainfall for July at 286.3mm as opposed to a normal mark of 210.6mm, but the spread across the Capital was not equitable, with one station logging showers lower than 150mm and one pushing close to the 400mm mark.

Data from the India Meteorological Department (IMD) highlights this gulf — Mayur Vihar, for instance, got 396.5mm in rainfall in July while Najafgarh in southwest Delhi recorded only 148.4mm of rainfall.

Experts say that Delhi, and many other tropical cities in other countries, are increasingly seeing a phenomenon that was missing till a decade ago – the formation of thunderclouds during the monsoon months that bring intense spells of rainfall in isolated parts of the city. This change may be linked to the climate crisis, and may also occur due to localised factors such as the relationship between concretised and green spaces and the density of buildings in an area, the experts added.

Also read: July ends with 8% excess rainfall but uneven distribution, says IMD

“Such uneven distribution of rainfall is generally a characteristic of convective clouds, which form in the pre-monsoon periods, and are typically thunderclouds that have formed within a matter of hours, due to high moisture and high air temperature. During the monsoon months, we used to get altostratus clouds, which are very thick and spread across an area of hundreds of kilometres, bringing fairly uniform rain over a city. Over the last decade or so, we are seeing these altostratus clouds are not forming as much, and instead, you are getting thunderclouds even during the monsoon period, which could provide intense rainfall in a small area of a few kilometres,” said Mahesh Palawat, vice president of meteorology at private weather forecaster Skymet.

He said that due to the climate crisis, the air temperature is gradually rising, which also increases its capacity to hold water. “This leads to vertical cloud formation instead of horizontal, which leads to more rain over a fixed area as compared to wider areas.”

This shift appears to have been reflected in IMD data. While Mayur Vihar recorded 396.5mm of rainfall, the Sports Complex station at Akshardam – barely a few 5km away, received only 157.9mm of rainfall in July. The Ayanagar station in southwest Delhi received 254.6mm of rainfall, as opposed to 207.1mm of rainfall in Palam, also in sothwest Delhi about 15km away. Similarly, the Pusa automatic weather station (AWS) recorded 326.8mm of rainfall across the month – the second highest for all Delhi stations — while a part-time observatory at the President’s estate, about 7km away, recorded 225.9mm of rainfall.

RK Jenamani, scientist at IMD, says it is difficult to pinpoint one reason to such a spread, but added that the movement of clouds and the topography of the area could be playing a role.

Also read: Normal monsoon rainfall likely in August-September: IMD

“We have largely seen easterly winds, so all weather systems are entering from south-east Delhi and moving towards northwest. This could be a factor on why some parts of southwest Delhi did not receive adequate rainfall, however one also has to see other factors such as the land-use pattern, the role of water bodies and green cover. If some spaces are hotter than others, they are likely to influence the clouds and lead to either them vapourising quicker or changing their movement,” he said.

On Monday, no rainfall was recorded at any station in Delhi, barring Jafarpur, which received 1mm of rainfall between 8.30 am and 5.30 pm, IMD data showed. IMD has forecast very light rain and isolated drizzling in the city on Tuesday.

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