Shorter, more intense rain spells a flood worry for Delhi
Over the last decade, the Capital has been receiving shorter and more intense spells of rain, scientists from the India Meteorological Department (IMD) said, a change in monsoon patterns that is the primary reason behind increasing instances of urban flooding and flash floods in Delhi and the National Capital Region (NCR).
Rainfall data maintained by the Indian Institute of Tropical Meteorology (IITM) in Pune shows that in the 1980s and 1990s, in July, Delhi used to record 15-20 rainy days on an average, which in the last decade has reduced to eight to 10 days. Met officials concurred, and said that rainfall in the Capital used to be distributed more uniformly, but it is now seen in short and more intense episodes.
An example of this can be seen in this year’s monsoon pattern.
Despite a slow start to the monsoon, the Capital, with just five days of heavy rains has managed to record a rainfall surplus of 27% so far. Till July 17, Delhi rainfall was at a deficit of 51%. The usual date for monsoon arrival in Delhi is June 27, but the onset this year was 16 days late, and the Capital received its first monsoon shower on July 13.
After the onset, the city has got rain on only five days. In these days alone, 248.2mm rainfall has been recorded, as against the usual 192.9mm.
The hourly rainfall recordings between July 18 (8.30am) to July 19 (8.30am) at the Safdarjung observatory showed 69.6mm rainfall, while the Palam weather station received 99.3mm rains, Lodhi Road 62mm, the Ridge 58mm, and Aya Nagar 51.6mm.
Madhavan Nair Rajeevan, secretary of the Union ministry of earth sciences, also said that the rain spells in Delhi were getting shorter, but more intense.
“The number of rainy days is decreasing, but when it rains, it rains very heavily for short periods. This is a pattern that we have been observing not just in Delhi but in many metro cities. When this happens, instances of flash floods in cities increase because rainfall that was supposed to have spread across say, a week, is now being received in a day,” Rajeevan said.
Flash floods are a sudden flood of water caused by heavy rainfall in a region. Over the last two days, when Delhi and NCR recorded intense showers, the Capital, and satellite towns such as Gurugram saw massive flooding that led to roads, footpaths, underpasses and even residential and office buildings being inundated.
In Delhi’s Pul Prahladpur a 27-year-old drowned in flooded underpass, and a nine-year old boy died after drowning in a rain-water filled pit in outer Delhi’s Metro Vihar on Monday.
To be sure, one big reason for this is lack of maintenance and cleaning or de-silting by the various agencies of the Delhi and Gurugram administration.
Mahesh Palawat, vice-president (meteorology and climate change) at Skymet Weather, a private forecaster, attributed the change in monsoon patterns to the climate crisis.
“Earlier, rains in Delhi continued for three or four days. And this rain used to be from altostratus clouds, but this type of cloud has almost stopped forming in the tropics now,” said Palawat.
“Air temperatures are increasing because of the climate crisis and global warming. When this happens, the moisture-carrying capacity of the air also increases. This leads to the formation of intense clouds, called convective clouds, which are capable of producing heavy thunderstorms and rainfall in shorter periods,” he added.
Forecasters said that, in the coming years, such short, intense spells are likely to increase and cities must prepare for increased urban flooding.
“There is no doubt that such instances will only increase in the coming years. IMD has recently come up with a flash floods warning system and scientists are experimenting with advancing the technology further. However, we can keep giving warnings, but there should also be a plan to act upon these warnings. Cities should be prepared on how, within a span of three to four hours, we can respond to flash floods, evacuate public places etc,” Rajeevan said.
Urban planning experts also stressed on the need to redesign cities keeping this scenario in mind.
Sewa Ram, professor (transport planning) at the School of Planning and Architecture, said that flooding during heavy showers is unavoidable on concretised surfaces, which water cannot percolate through. So, the way forward has to be to find innovative ways to design roads and drainages.
“The trend of urban floods is not new anymore. We must go back to the drawing board, study our roads and drainage systems and come up with ways in which water stagnation reduces. Old drainage systems must be redone, so that they can flush out more water,” Ram said.