Climate Change and its Impact on the Hydrology of a Glaciated Mountainous Region

Climate change significantly impacts the hydrology and water resources of any region especially high mountain areas including cryosphere that consist of glaciers. Numerous studies report that glaciers are retreating and losing volume with time causing serious concerns over freshwater availability in the basins they feed water to. Assessment of these changes and their relationship with various climatic aspects are crucial to understand and tackle such challenges. Long-term trends in temperature and precipitation and their spatio-temporal distribution, for the mountainous state of Uttarakhand in India were assessed, utilizing the India Meteorological Department’s gridded precipitation and temperature datasets for the period 1951-2023. Mann-Kendall trend test was performed at 90% significance level, for each grid, to check monthly trends, which gave critical insights upon shifts in seasonal meteorology. Results reveal notable changes in the monthly distribution of precipitation with many grids reporting a decreasing winter precipitation (Oct-Jan) and many showing an increasing precipitation for May and August. Global warming impact is much visible through changes in minimum temperatures for almost all the grids, reporting a strong positive trend for February, March, August, September and November. Importantly, these changes are more prominent for the high-altitude areas, which highlights elevation dependent climate change pattern. Evidently, the precipitation is shifting from winters to summers and the minimum temperatures are increasing towards the end of ablation season (Aug-Sep), decreasing the chances of receiving solid precipitation or snowfall. Consequently, a decrease in snow cover is expected in the future, which from a hydrological perspective, would lead to a reduction in snowmelt discharge and its contribution to streamflow of the Himalayan perennial rivers. Moreover, the increasing temperature and precipitation during summers can generate huge discharges from glacierized catchments due to increased simultaneous contribution of glacier-melt and rainfall, causing destructive flash floods and debris flow events, as being witnessed in the recent past. Combination of decreased precipitation in winter months and increased temperatures overall, can prove detrimental to glaciers’ health as they will melt more, whereas their replenishment will be lesser, leading to negative mass balances. Climate change is certainly having an adverse effect on the mountain hydrology, especially that of the Himalayan cryosphere. The glaciated catchments are expected to have more glacier-melt and rainfall-runoff contribution and less snow-melt contribution in the near-future. The glaciers, present in the region, are expected to retreat and lose mass more rapidly, considering the meteorological changes in the high elevation areas. Small glaciers might deplete faster, which would lead to problems of freshwater availability in the nearer downstream areas dependent on the melt-runoff water. While there seems no immediate solution to the prevailing scenario of climate change, community-based measures can be adopted to tackle problems of water availability. Water conservation and springshed management in the mountainous regions are some focus areas to work upon, in order to ensure water security under the changing climate.