Following the record-breaking warmth on Sunday, temperatures dipped again as an active Western Disturbance brought rain on Monday
The northern part of the country has seen a see-saw of weather extremes over the past two months. Such acrobatics of weather not only affects agriculture in the region but also impacts human health.
For instance, Delhi was experiencing moderate cold conditions on Saturday, but on Sunday it suddenly saw temperatures rise exorbitantly—which meant that the city experienced its warmest January day in a decade. This is when December turned out to be the third-coldest month in Delhi in the last 50 years.
The average minimum temperature during December 2018 was 6.7° Celsius—this happened last in 2005 when the average minimum temperature in December was 6° Celsius, preceded by 1996 when it was 5.9° Celsius.
Following the record-breaking warmth on Sunday, the temperatures have dipped again as an active Western Disturbance (WD) brought rain to the city on Monday. The seasonal weather conditions have been no different.
At the start of December 2018, the India Meteorological Department (IMD) had stated that the winter season (two months of December and January) will be warmer than usual. This turned out to be true for only about three weeks.
On December 19, 2018, IMD announced that dry cold wave and ground frost conditions were prevailing in Rajasthan, Punjab, Haryana and Delhi. The next day, the weather agency found that cold wave conditions had reached as far as Gujarat and Madhya Pradesh.
Based on the prevailing conditions, Down To Earth had reported that there could be a spurt in H1N1 influenza cases in the states which suffered from poor post-monsoon rainfall and cold conditions.
This turned out to be true as over 50 people died of the virus in just one month, 49 of them only in Rajasthan. This substantiated the fact that prevailing weather conditions can have a direct influence on human health.
The reason for this was a lack of strong WDs coming into India from the west. WDs are extra tropical storm systems which originate in the Arctic, Mediterranean and Middle Eastern regions and travel towards Afghanistan, Pakistan and India.
While usually there are three-five strong WDs in December, there was only one in last one. WDs are known as winter monsoon in the northern part of the country and are essential for the Rabi cropping season as they maintain the required moisture in the soil and air.
The feebly active WDs that did arrive limited themselves to the hilly states of Jammu & Kashmir, Himachal Pradesh and Uttarakhand, and did not influence the weather in the northern plains which made the cold wave conditions persist for longer than usual.
On January 3, IMD said the cold wave conditions were still prevalent at many places across north India till the end of December, but this was broken by a wet spell brought in by a fresh WD in early January.
Then the cold was back with record breaking ground frost conditions across states. States that are not usually victims of such conditions were also affected. For example, Munnar in Kerala recorded temperatures as low as -3° Celsius in that week.
“One of the reasons for less WD activity in the plains could be mid-0 and north latitude interactions forcing reduced southward propagation of WDs. Another factor which might be working against the WDs could be the lack of moisture coming in from the Indian Ocean and the mid-latitude Mediterranean region which generally feeds them,” AP Dimri, an expert on WDs at the School of Environmental Sciences, Jawaharlal Nehru University, had told Down to Earth.
However, the exact reasons for this phenomenon are still unknown. Dimri had further predicted that the WDs could be back with greater intensity in January.
Currently the IMD has forecasted an elongated active wet spell with rains and snow in many parts of north and north-west India as a result of two intense back-to-back WDs till January 26. The IMD has also put out a detailed forecast of the weather conditions in different states across the coming week or so.
It has even warned of possible thunderstorms and hailstorms in some areas of Punjab, Haryana, Chandigarh, Delhi and Uttar Pradesh—which could lead to crop losses. The first of the WDs has already started impacting the weather in the national capital exactly as IMD had predicted. There was also some rain and snow in the state of Jammu and Kashmir on January 20.
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