How western disturbances are keeping Delhi weather in a flux
So far, the Safdarjung weather station has recorded eight heat wave days in April, the highest since 2010 when 11 such days were recorded, according to R K Jenamani, scientist, IMD.
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Monkeys drink water from a fountain at Rashtrapati Bhavan in New Delhi on Friday. (Express Photo: Praveen Khanna)Over the past six months, variations in the intensity and locations of western disturbances have brought heavy rainfall to Delhi during some months, and kept the city dry and in the grip of a heat wave at other times.
Last year, the national capital witnessed the rainiest October in 65 years, with the Safdarjung weather observatory recording 122.5 mm of rainfall against a normal of 28 mm, on account of western disturbances. Western disturbances are storms that originate in the Caspian or Mediterranean Sea, and bring non-monsoonal rainfall to northwest India, according to the IMD.
Excess rainfall was also recorded in January and February this year. In contrast, there was no rainfall in November and March, and the summer saw an unusually early start with heat waves setting in at the end of March. Multiple western disturbances that brought cloud cover had also kept the maximum temperature low in February, when the lowest maximum temperature in 19 years was recorded. Active western disturbances eluded northwest India in March, and absence of cloud cover and rain allowed temperatures to remain high.
Does climate change have a role to play in the pattern of western disturbances, leading to record-breaking rainfall and heat? Prof A P Dimri at the School of Environmental Sciences, JNU, said the frequency of western disturbances has increased, but not the precipitation associated with them, partly due to a warming atmosphere.
“Western disturbances are low-pressure areas. If it is a feeble western disturbance it will not have moisture to precipitate. For precipitation, you need moisture, and by virtue of a warming atmosphere, there is less amount of moisture available to precipitate. Simultaneously, because of warming in atmosphere, western disturbances are going higher in elevation. In general, they move in subtropical westerly jet, now they are becoming lighter and moving higher, above 200 hectopascals,” he said.
So far, the Safdarjung weather station has recorded eight heat wave days in April, the highest since 2010 when 11 such days were recorded, according to R K Jenamani, scientist, IMD. Under the influence of a western disturbance, the heat wave spell was broken recently, with the city receiving very light rainfall. The impact of western disturbances is not about their number, but about their location and intensity, Jenamani explained. These are natural variations, he added.
Mahesh Palawat, chief meteorologist and vice-president at Skymet Weather, a private weather forecaster, said, “In 2020, we saw excess rainfall in Delhi in March. This year we saw feeble western disturbances in March that did not give any pre-monsoon weather activity even over the hills. Similarly, in November, there was little rainfall and snowfall over western Himalayas, though intensity of western disturbances usually increases in November. By March usually, the intensity and frequency start decreasing as western disturbances start travelling in upper latitudes.”
Variations will have to be monitored over the next few years to determine what climate change impact might be, he added.
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