Warmer Winters for North India, Colder Winters for South India. Climate Change?

The winter season in India this year is predicted to be colder than normal for the southern region of India whereas it is going to be warmer than normal for the northern region of India, as per the data from the seasonal outlook for temperatures and rainfall by the IMD.

The warm temperatures in the region would also be accompanied by a dry period in December as IMD has forecast below-normal rainfall for most of India in the month. This scenario is unusual in the northern states which are known for their frigid winter season while the southern states have mild winter seasons. This means the frequency of days with maximum and minimum temperatures about 2 to 4 degrees C above normal will be higher during the next 3 months. 

Below-normal minimum temperatures are likely to be seen over many parts of peninsular India, some parts of central India, and isolated parts of northwest India. However, overall normal to above normal minimum temperatures are most likely over many parts of northwest India (Punjab, Uttarakhand, Haryana, Delhi, Himachal Pradesh, Jammu and Kashmir, and some areas of Rajasthan) and parts of northeastern India. Whereas above-normal maximum temperatures are likely to be over most parts of northwest India, east, and northeast India, and many parts of Central India.

Areas most affected due to warmer than normal winters

The most drastic impact would be on Jammu and Kashmir where there is about a 55-75 percent chance of warmer than-usual nights. This could also be the case for Himachal Pradesh, most parts of Uttarakhand as well as the northeastern region. The warm days would be prevalent across much bigger areas as there is a good chance of above-normal maximum temperatures in western parts of Rajasthan, areas of Punjab, Haryana, and Uttarakhand. The entirety of northeast India has a 55-75 percent chance of warmer-than-normal days. 

The impact of the above-normal day and night temperatures in hilly regions of Jammu and Kashmir, Uttarakhand, Himachal Pradesh, Sikkim, and Arunachal Pradesh could be witnessed in the form of glacier melting in these regions. These states were also impacted by early and intense heat waves in the spring and summer seasons of this year from March to May. This is contrary to the condition in southern India, where maximum areas would experience colder than normal days and nights. The rainfall for December in south India this year would be normal, according to IMD.

EL Nino, La Nina and Climate Change

La Niña is the large-scale cooling of the temperature on ocean surfaces in the central and eastern equatorial Pacific Ocean. It is coupled with changes in the tropical atmospheric circulation, like winds, pressure, and rainfall. Thus, it is a climate pattern that describes the cooling of surface-ocean water along the tropical west coast of South America. It mostly has the opposite impacts on weather and climate as El Niño, which is the warm phase of the El Niño Southern Oscillation or ENSO. ENSO has an influence on weather and climate patterns like heavy rains, floods, and drought. In India for example, El Nino is associated with drought or weak monsoon while La Nina is associated with strong monsoon and above average rains and colder winters. 

According to Dr. Partha Das, Head of Water, Climate & Hazard Division, Aaranyak, “IMD’s winter forecast also indicates its correlation to the persisting La Nina, one of the longest La Ninas in the recent climatic history of the planet. Since the intensity and persistence of both El Nino and La Nina have been found to be affected by climate change, it’s fairly likely that climate change could be the main trigger of the projected warmer winter for some regions of India during December, January, and February 2022-23. However, the warming winters have been the average climatic trend in many parts of the country, including northeast India. Therefore, the warmer days and nights in the next three months could be a continuation of the same trend.” 

Dr Das also added that “On the other hand, there were other projections in the past that anticipated an increase in winter temperature in the South Indian region. However, now we have the IMD indicating the probability of a chillier winter in the south. This shows inconsistency in various prediction models, which is not unusual given the multiplicity of factors that are at play to determine the short-term weather features. Approach to modeling and use of specific data are also other factors that may yield varying results.  However, there is no doubt that all fluctuations of weather and climatic patterns from the long-term normal modes, if seen to be consistent over a few years, could be an indication of climate change. But one must remember that it is the same climate change as an overarching factor that can cause short-term deviations which could have a significant impact on humans and the environment.” 

Impact on Crop yields 

The impact of above-normal temperatures will be on the ongoing rabi crop season, particularly wheat, depending on the stage of the wheat crop. The combination of the dynamic behavior of weather and dynamic stages of vegetation in wheat crops determines the impact. A mild winter can be good for rabi crops, but a warm winter can also have a negative impact. Farmers in such conditions have to deal with more weeds, and bugs which pose a threat to crops.

“Large variations from LPA temperatures in the winter, be it in the maximum temperature or in the minim temperature could also be detrimental to plant phenology, crop development, and productivity. Therefore, this forecast allows us to provide proper weather and agricultural advisories to our farmers since our rabi crops cultivated in the post-monsoon and winter season are highly sensitive to temperature, soil moisture, and rainfall. Farmers should be advised about appropriate measures to be taken in terms of timing of sowing, farming technique, and other precautions,” Dr. Das said.

IMD’s analysis

Dr. Mrutyunjay Mohapatra, Director General of the IMD was quoted as saying by the Hindustan Times, “La Nina is only one of the factors, not the only factor which determines temperatures. In November also La Nina was also there. You expect more cyclonic disturbances during La Nina period but there was only one depression. Madden–Julian oscillation (MJO) was active which subdued cyclonic activity. We use a dynamic modelling system which are influenced interactive large scale global features.”

Mohapatra explained the warmer winter may be due to two reasons. “We can speculate that the western disturbance activity may be subdued leading to less cloudiness and both above-normal day and night temperatures. There may be higher penetration of easterly winds which may cause temperatures to rise but not bring enough moisture so as to cause rainfall,” he said.

“Yes, minimum temperatures were above normal over most parts of northwest India by 1 to 2 degrees C. This was mainly because of less influence on western disturbances. There were 5 western disturbances but 3 of them moved to the north of Indian latitude and did not help us. The maximum temperatures were normal to near normal about 1 degree C here and there,” Mohapatra added.

(with inputs from Aayushi Sharma)