Delhi logged more than 20 mm of rainfall in April, the highest in the month since 2017.
A fresh spell of rain drenched Delhi on Wednesday, taking the total precipitation recorded this pre-monsoon season to 184.3 mm which is 186 per cent more than normal rainfall, according to the India Meteorological Department.
Copious rainfall has also yielded the best air quality in the January to May period in the city since 2016, barring 2020 which saw strict lockdowns to contain the spread of COVID-19.
May, generally the hottest month in Delhi with a mean maximum temperature of 39.5 degrees Celsius, recorded 111 mm of rainfall this time, which is 262 per cent more than the long-term average of 30.7 mm.
This is also the fourth highest rainfall in the month after 165 mm in 2008, 144.8 mm in 2021 and 129.3 mm in 2002, according to IMD data.
The city logged more than 20 mm of rainfall in April, the highest in the month since 2017, and heatwave conditions at isolated pockets.
Meteorologists attributed the excess rainfall and below-normal temperatures this pre-monsoon season (March to May) to higher-than-usual western disturbances -- weather systems that originate in the Mediterranean region and bring unseasonal rainfall to northwest India.
"Usually, five to six western disturbances are recorded in the northern plains in April and May. This time, we saw 10 western disturbances, mostly strong ones," said Kuldeep Srivastava, the head of the Regional Forecasting Centre of the IMD.
"This is unusual. However, we cannot link it to climate change in the absence of data. There is no definite trend," he said.
Delhi recorded maximum temperatures above the 40-degree mark for just nine days in May with heatwave conditions affecting some parts for two days.
"The Safdarjung Observatory, which is representative of Delhi, has not recorded any heat wave in the pre-monsoon season this year. This has happened for the first time since 2014," Srivastava said.
The weather station recorded 13 heatwave days in the pre-monsoon season last year -- nine in April and four in May. It saw just one heatwave day during this period in 2021, four in 2020 and one in 2019.
The threshold for a heat wave is met when the maximum temperature of a station reaches at least 40 degrees Celsius in the plains, 37 degrees in the coastal areas, and 30 degrees in the hilly regions, and the departure from normal is at least 4.5 notches.
According to the Commission for Air Quality Management (CAQM), Delhi recorded an average air quality index (AQI) of 213 in the January to May period this year, the lowest since 2016, excluding 2020.
It was 237 during the corresponding period last year, 235 in 2021; 181 in 2020; 236 in 2019; 242 in 2018; 251 in 2017 and 283 in 2016.
According to the IMD, a fresh western disturbance will bring gusty winds and rain to the plains, including Delhi, starting June 1. The Met office has issued a yellow alert, cautioning people about traffic disruption and waterlogging in low-lying areas on Thursday.
The maximum temperature is predicted to remain below the 40-degree mark until June 5.
Earlier this month, the weather office predicted below-normal maximum temperatures and fewer heatwave days in northwest India in May.
With the IMD anticipating a slight delay in the arrival of the southwest monsoon, the maximum temperatures are likely to remain above normal for a longer-than-usual period in June.
"During June, normal to above-normal maximum temperatures are likely across most parts of the country, except for the extreme north and some parts of the southern peninsular region," the IMD said.
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