The snow cover of the Himalayas in Himachal Pradesh that feeds four major river systems is down by 18% in a year, indicating climate change.
A government study has found that 23,542 sq km was under snow cover in 2019-20, which dropped to 19,183 sq km in 2020-21, a decline of 3,404 sq km or 18.52%.
The Centre on Climate Change of the Himachal Pradesh Council for Science Technology and Environment (Himcoste) and the Space Applications Centre, Ahmedabad, conducted the study to assess spatial distribution of seasonal snow cover in Himachal Pradesh from October 2020 to May 2021.
“Scientists used space technology to study the cyrosphere, comprising the glaciers over the Himalayas in Himachal Pradesh. Satellite data was analysed to map the geographical extent of snow cover and understand the contribution of snow in catchments to sustain the hydrology of the river basins,” Himscote member secretary Sudesh Kumar Mokhta said.
Fluctuating trends affect weather cycle
“If there is a shift in snowfall pattern, as has been observed over the past few years, the long-term implications will be on water availability in the river basins as the seasonal snow cover contributes to the river discharge during the lean season,” said SS Randhawa, a principal scientist at Himcoste, who headed the study team.
The late snowfall patterns that extend into summer are not sustainable as it melts fast due to more water content. Similar trends were observed during the 2020-21 winter that was comparatively warmer, he said.
If such fluctuating trends continue for long, they affect the weather cycle, resulting in erratic rain, snowfall and heat and ultimately water availability.
Himachal Pradesh gets winter precipitation in the form of snow at the higher altitudes. About one-third of the total geographical area of the state remains under thick snow cover during winter.
Most major rivers such as the Chenab, Beas, Parvati, Baspa, Spiti, Ravi, Sutlej and their perennial tributaries originating from the Himalayas depend on the seasonal snow cover for their discharge dependability.
Four major river basins record area reduction
“Data analyses show that all four major river basins in Himachal, namely the Ravi, Sutlej, Chenab and Beas, recorded reduction in terms of the total monthly average area in 2020-21,” said Randhawa.
The snow cover in the Chenab basin fell from 7,154.12 sq km in 2019-20 to 6,515.92 sq km in 2020-21, a reduction of 638.2 sq km.
The Beas basin shows a decrease of about 19% with its average snow cover area having decreased from 2457.68 sq km to 2002.04 sq km, a loss of 455 sq km.
The Ravi basin saw an overall reduction of 23% in the total area under snow cover. This year, the basin recorded snow cover of 1,619.83 sq km compared to 2,108 sq km last winter. The reduction in terms of area under snow cover was 488 sq km.
Snow cover in the Sutlej basin shrunk by 2,777 sq km (23%). It was 11823.28 sq km in 2019-20 and 9,045.51 sq km this year.
Less snowfall affects runoff patterns
In the beginning of winter in October 2020, all basins were characterised by less snow cover area and the decrease of about 51% in the Chenab, 64% in Beas, about 77% in Ravi and 72% in the Sutlej. It was 31% in case of Chenab, 6% in Beas, 52% in Ravi and 21% in the Sutlej basin in November.
In January, the Chenab basin shows a decrease of about 2%, the Beas 27%, Ravi 16% and Sutlej 24%. The four river basins again show a decrease of 2%, 27%, 16% and 24%, respectively.
It indicates there was less snowfall during the 2020-21 winter, which may affect the runoff patterns during the summer. However, the marginal increase of 8% and 1% in Chenab basin and the Sutlej basin, respectively, indicates that the winter precipitation has extended to the summer months.
An analysis of summer months reveals that in the Chenab basin, 85% of the total basin area in April and 71% in May is still under the impact of snow, reflecting that about 14% of the total basin area melted during this period.
“In other words, we can say that 52% of the total basin area would melt during the next ablation month (June to August), meeting the discharge dependability from the Chenab basin,” Mokhta said.
Likewise, the Beas basin in April had 49% of the total basin area and in May about 35% was under snow cover impact, whereas in the Ravi basin, 29% of the total basin area in April and 24% was covered with snow.
The Sutlej basin, comprising Baspa, Pin and Spiti rivers, indicates that 41% of the total area in April and 37% in May was under snow.