Nauni varsity study indicates a shift of western disturbances

Scant rainfall coupled with the rise in temperature may alter the cropping calendar of Rabi crops in the state. Chilling requirement of pome and stone fruits will also be affected owing to the inclement weather triggered by weak western disturbances (WDs) which are responsible for the winter rains.

“A long-term study from 1971-2022 conducted in the Department of Environmental Science, Dr YS Parmar University of Horticulture and Forestry, Nauni, Solan indicated a shift of WDs from the winter months to April and May month. During the post-monsoon and winter months of the year 2024 and first fortnight of January, 2025, the region has been facing longer dry spells due to weak WDs” observed Dr Satish Bhardwaj , Head of Department, Nauni varsity.

The clear sky in mountainous areas of the state has led to a rise in temperature during the day-time and nights leading to enhanced radiative cooling triggering cold wave conditions and frost in the region. The long-term analysis of weather data also indicated a rise in the temperature and increased frequency of warm winter days in hills.

In Solan, the long-term average maximum and minimum temperature for January month is 17.8 degree C and 2.3 degree C, respectively. However, the maximum temperature anomaly based on the long-term data from 1991-2022 indicated an increase of 0.03 degree C per year while minimum temperature anomaly indicated a decrease of 0.01 degree C per year during this month in the district.

On January 4 this year, Solan experienced exceptionally warm conditions with a recorded maximum temperature of 29 degree C. This was close to the high temperature witnessed in the drought year of 2009. In Solan district, the maximum temperature anomaly demonstrated a more pronounced rise of 0.07 degree C per year during the winter season. The prolonged clear sky conditions, weak or delayed western disturbances, down slope winds and atmospheric stability conditions are causing a rise in the temperature.

The northwestern region of India receives most of its rainfall during the southwest monsoon season.

As much as 30 per cent rain is received during the remaining part of the year and about 15 per cent of its annual rainfall occurs during the winter season, primarily due to WDs.

“These extra-tropical weather systems originating from the Mediterranean Sea, play a crucial role in the winter climate, contributing to snowfall in higher elevations and rainfall in the lower areas. During the post-monsoon and winter seasons, rainfall from WDs plays an important role for sustaining rainfed agriculture, supporting hydroelectric projects, and meeting the demand for drinking water,” explained Dr Bhardwaj.

The winter rainfall serves as a vital source of livelihood for the people of the state. The weak and reduced frequency of WDs has led to lesser cloud cover, rain and snowfall. Scientists advised the farmers follow the crop-based weather advisories issued by CSK Himachal Pradesh Agricultural University, Palampur and Nauni varsity.