Ever since the inception of the State Centre on Climate Change under the aegis of the HP Council for Science Technology and Environment (HIMCOSTE) by the Government of Himachal Pradesh, the Centre has been involved in undertaking various studies to understand the impact of climate change on its various facets. The Centre has successfully utilized the applications of space technology in carrying out studies related to Cyrosphere comprising the snow and glaciers in Himachal Himalayan collaboration with Space Applications Centre (ISRO), Ahmedabad,Govt of India.The Cryospheric studies are important as the one third part of the State is characterised by this great Himlayan reserve and the studies of which using any other conventional method is not possible due to inaccessibility of this area.
Himachal Pradesh receives 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 the winter season. Most of the major rivers like Chenab, Beas, Parvati, Baspa, Spiti, Ravi, Satluj and its perennial tributaries originating from the Himalayas depend upon the seasonal snow cover for their discharge dependability. Besides this, the snow cover also helps in controlling the accumulation and ablation patterns of the glaciated regions in the State.
Considering the importance of seasonal snow cover as a major input in controlling the hydrology of the river basins, Director (Env.S&T)-cum-MemberSecretary (HIMCOSTE) D.C.Rana informed that although we have the information about the total snow fall that takes place during winter season from the various observatories operating through out the State as a point information and therefore its spatial extent cannot be ascertained. Thus by using satellite data of different resolutions, it has now become possible to map the geographical extent of the area covered under snow during winter season. He further said that the studies which are being carried out by the Centre for mapping of seasonal snow cover in terms of its spatial distribution covers the different river basins in Himachal Pradesh during the winter season from October to May and is an important input in order to understand the contribution of snow in different catchments to sustain the hydrology of the river basins.
Considering the present trend of winter snowfall in Himachal Pradesh, the winter precipitation was mapped in all the basins viz Chandra, Bhaga, Miyar, Beas, Parvati, Jiwa, Pin, Spiti and Baspa using AWIFS satellite data having spatial resolution of 56 mts from October to May. During 2019-20 snowfall was estimated and analyzed with reference to the average value of the total area under snow in each month from October to May in 2018-19.
In 2019-20 winter in the south eastern part of the State there was more snow covering mainly the Satluj basin as compared to the other basins i.e. Beas and Ravi basins respectively, whereas the Chenab basin has not shown much change in the snow cover area in 2019-20 when compared with 2018-19. The other winter months i.e. October, February and March, all basins show less snow cover area in 2019-20 in comparison to 2018-19 indicating that the winter precipitation after January has declined during the remaining winter months.
The analysis of summer months i.e. April and May revealed that in Chenab basin, about 87 percent of the total basin area in April and about 65 percent in May is still under the impact of snow reflecting that snow in about 22 percent of the total basin area has melted out between April and May. In other words, we can say that about 65 percent of the total basin area would melt during the next ablation month (June to August) contributing in the runoff from Chenab Basin.
Likewise, the Beas Basin in the month of April has about 49 percent of the total basin area and in May about 45 percent has snow cover impact reflecting that snow in about 4 percent of the total basin area has melted out in Beas basin between April and May and thus about 45 percent of the total basin area of Beas would be available for meeting the water requirements from snowmelt during the next ablation months in summer.
The Ravi basin reflected that about 44 percent of the total basin area in April and about 26 percent in May of the total basin area is under snow cover impact reflecting that snow in about 18 percent of the total basin area has melted out between April and May and thus only 26 percent of the total basin area would be available for meeting water requirements from snowmelt of the Ravi basin during next ablation months.
Likewise, the Satluj basin comprising of Baspa, Pin and Spiti indicates that about 72 percent of the basin area in April and about 50 percent in May is under the snow cover reflecting that snow in about 22 percent of the basin area in Satluj has melted between April and May and the remaining 50 percent would be available for meeting the water requirements from snow during next summer months in 2019-20
To summarize based on the analysis carried out from snow cover mapping in Himachal Pradesh during 2019-20 (October to May) a marginal decrease of the order of about 0.72 percent in the area under snow has been observed in Himachal Pradesh in comparison to the total area during 2018-19 i.e total average area under snow in 2018-19(20210.23Km2) has reduced to 20064.00Km2 in 2019-20.Further during peak winter months, the snow cover area has reduced gradually from February onwards which may affect the runoff patterns during the summer months. Based on the data analyzed, more snow cover has been observed in Satluj basin during winter months (November to January) than the Beas and Ravi basins, whereas Chenab basin has not shown much change in the area under snow during this period. Based on summer month analysis, in Chenab basin (65 percent of the total basin area) and Satluj basin (50 percent of the total basin area) will contribute as snow melt in the river system after May onwards in comparison to Beas basin (45 percent) and the Ravi basin (26 percent) of the total basin area in 2020.