Strong La Nina conditions prevailed during the fall of 2020 and the winter season (Jan-Feb) 2021. Oceanic Nino Index ( Nino 3.4) remained -ve and below the threshold of -0.5°C between August 2020 till March 2021. To work out the Oceanic Nino Index (ONI), an average of three months of the Nino3.4 index is taken. To be classified as a La Nina episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons. In the last La Nina episode, the quarterly indices remained <= -0.5°C, between Jul-Aug-Sep 2020 to Apr-May-Jun 2021. La Nina conditions were fairly strong from October 2020 to February 2021, with ONI in excess of -1°C. Accordingly, Jan & Feb 2021 literally starved for rain and snow in the plains and hills of North India.
La Nina conditions are constantly building up this season also and the La Nina advisory is already in place. La Nina is likely to become more powerful between December 2021 and February 2022. Prevailing conditions have already impacted the rainfall in November and the first 1/3rd of December. There is no likelihood of any rainfall for the next 10days in the plains of North India and not much of snowfall over the hilly states. Therefore, total rainfall/snowfall for Nov-Dec2021 for the northern states will possibly end up in a large deficit.
La Nina conditions may not have as strong co-relation as El Nino, yet they are known to suppress the rainfall in the sub-tropical region (20-30°N). The western disturbances also track more to the north and therefore snowfall remains scanty across the hills. This leads to dry and icy winds from the far northern parts of Asian countries sweeping down the slopes and penetrating the mountainous region of India. The chill factor increases and below normal temperatures are recorded during the peak winter period between the last week of December to the 1st week of February. It happens even in the United State of America. During La Nina events, winter tends to be drier and warmer than normal across the southern U.S and cooler and wetter in the northern U.S. and Canada.
The upcoming winter season of Jan-Feb 2022 faces the risk of being drier and colder than normal for the northern parts of the country. Any major shortfall affects tourism, agriculture, horticulture and snow sports.
Lack of rain and snow during this period disturbs the ecological balance and leads to anxious moments of water scarcity for the subsequent season. Keep your fingers crossed, as the La Nina conditions will continue till early spring season 2022.