Warming over north Arabian Sea and northward shift of southwesterly winds have allowed low-pressure systems to travel far inland towards northwest India
The incessant rain September 22, 2022 that has brought the entire Delhi-National Capital Region to a standstill was caused by the interaction between three different weather systems, enhanced further by the ongoing La Niña phenomenon and a warming Arctic region.
The retreating monsoon winds, a low-pressure area over northwest Madhya Pradesh and a western disturbance are acting together over northwest India to bring the torrential rains, according to the India Meteorological Department (IMD).
Skymet Weather services, a private weather forecasting company based in Noida, predicted that the low pressure area, blocked by the monsoon winds and the western disturbance, may remain situated over northwest Madhya Pradesh and southwest Uttar Pradesh for the next two days, inducing more rainfall.
The rains have led to flooding in many areas, especially Gurugram, where schools have shut down and offices have asked employees to work from home.
The flooding and water logging in the cities is not just because of the rains. It is also due to the lopsided infrastructure development which gives no way for the water to be drained out.
The rains though have played their part and brought down the temperature of the capital city several notches below normal at 28 degrees Celsius September 22, according to IMD.
Delhi received 46.2 millimetres (mm) of rainfall between the morning of September 22 and the morning of September 23. This is more than 10 times its normal rainfall of 4.1 mm, according to data from the IMD.
In terms of absolute rainfall, the districts of South Delhi and East Delhi fared the worst, with 106.2 mm and 75 mm rains respectively. In terms of percentage, South West Delhi fared the worst, with 2,044 per cent excess rains.
But the rainfall did not just affect Delhi. Gurugram, from where the visuals and videos of water logging and stranded travellers went viral on social media websites, received 92.6 mm of rainfall which is a whopping excess of 2,887 per cent, highest in the state of Haryana.
In absolute terms, Faridabad received the maximum rainfall of 110.7 mm, an almost 2,000 percent excess. Overall, Haryana received 739 per cent excess rainfall between September 22 and September 23. Four other districts received excess rainfall greater than 1,000 per cent.
Western Uttar Pradesh received 696 per cent excess rains, with 13 districts receiving excess rainfall of greater than 1,000 percent. The highest absolute rainfall of 97.3 mm occurred in Etah district, which was an excess of 5,625 per cent.
Eastern Rajasthan received 453 per cent excess rains, with 11 districts receiving excess rainfall of greater than 500 per cent. Alwar (1,089 per cent) and Baran (976 per cent) districts were the worst-affected.
On September 23, IMD updated its prediction. It said a fresh western disturbance is also acting a little west of Rajasthan and the cyclonic circulation in the upper atmosphere associated with the low-pressure area remains.
Though there is also a trough from this cyclonic circulation towards the east up to the Bay of Bengal. This could bring rains to eastern Uttar Pradesh as well.
Normally, low-pressure systems that originate over the seas or oceans do not carry so much moisture so far inland. But that is now changing.
This had in turn made them interact with other weather systems, mainly western disturbances bringing moisture from the Mediterranean region and cause catastrophic rainfall, cloudbursts and subsequent floods, flash floods and landslides causing loss of life and property.
“The warming over the northern Arabian Sea and the northward shift of the southwesterly winds which produce less rain over Kerala and more rain over northern Maharashtra and Gujarat, have also allowed the low-pressure systems to travel inward towards the northwest,” Raghu Murtugudde, a climate scientist at the University of Maryland in the United States and Indian Institute of Technology, Bombay, said.
This northward shift of the south-westerly winds and the warming of the northern Arabian Sea are both direct consequences of global warming.
Murtugudde also contends that “La Niña is also playing a role now and some indication is there that the warm Arctic has added an upper level forcing to reinforce the rains.”
He had predicted back in July that such heavy rainfall would happen towards the fag end of the monsoon season and this may continue till the monsoon withdraws completely from the Indian subcontinent.
“I had commented back in July that I expect some fireworks in September because of the La Niña and the Arctic warming. They seem to be playing out now,” Murtugudde said.
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