The primary reason for the early onset of heat over northwest India is the lack of strong western disturbances
On February 20, 2023, Delhi recorded the third hottest February day since 1969 at the Safdarjung Observatory (33.6 degrees Celsius). According to the India Meteorological Department, the primary reason for the early onset of heat over northwest India is the lack of strong western disturbances (WDs).
The decline of La Niña conditions by March-April and the development of El Niño conditions later in the year could also mean further rise in temperatures and subsequent heatwaves. Due to this El Niño, the 1.5°C barrier could be temporarily breached in 2024.
WDs are storm systems that originate from the Caspian Sea and move across the Afghanistan-Pakistan region to bring rains across northwest India.
In the winter months, 4-5 disturbances travel with an average life cycle of 2-5 days. These are responsible for replenishing water in the northern Indian region in the form of snow and precipitation.
This month, feeble WDs have led to some precipitation in Jammu and Kashmir but temperatures are 5-7 degrees above normal in Uttarakhand and Himachal Pradesh.
There was an anticyclone (a high-pressure region) near the surface level of the Earth, which was centered over the northern parts of the Arabian Sea and adjoining northwestern parts of Gujarat. This high pressure pushed the air down and enhanced the inflow of dry winds from the northwest into India.
Since a strong WD has not been seen in some time, this dearth is also contributing to the temperature spike in north India.
In March last year, the warmest recorded in the country since 1901, the heat had caused a decline in the size and quantity of wheat yields. The rainfall was 71 per cent lower (8.9 mm) than its long time average of 30.4 mm.
Because of this experience, this time, the government is releasing its reserve wheat stock in the market to control already escalating wheat prices. A government advisory has also told farmers to “add mulch material in the space between two rows of vegetable crops to conserve soil moisture and maintain soil temperature”.
In December (Rabi cropping season for northwest and central regions), there was a countrywide rainfall deficit of 14 per cent. Northwest, central and east and northeast India were particularly dry with 83 per cent, 77 per cent and 53 per cent deficit in rainfall respectively.
Only the southern peninsular region received 79 per cent excess rainfall in that month. In January and February, 27 of the 36 states and Union territories received deficient, large deficient or no rainfall from January 1-February 15, 2023.
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