Abstract
Himalayan glaciers are the major source of fresh water supply to the Himalayan Rivers, which support the livelihoods of more than a billion people living in the downstream region. However, in the face of recent climate change, these glaciers might be vulnerable, and thereby become a serious threat to the future fresh water reserve. Therefore, special attention is required in terms of understanding moisture sources for precipitation over the Himalayan glaciers and the hydrograph components of streams and rivers flowing from the glacierized region. We have carried out a systematic study in one of the benchmark glaciers, “Sutri Dhaka” of the Chandra Basin, in the western Himalayas, to understand its hydrograph components, based on stable water isotopes (δ18O and δ2H) and field-based ablation measurements. Further, to decipher moisture sources for precipitation and its variability in the study region, we have studied stable water isotopes in precipitation samples (rain and snow), and performed a back-trajectory analysis of the air parcel that brings moisture to this region. Our results show that the moisture source for precipitation over the study region is mainly derived from the Mediterranean regions (>70%) by Western Disturbances (WDs) during winter (October–May) and a minor contribution (<20%) from the Indian Summer Monsoon (ISM) during summer season (June–September). A three-component hydrograph separation based on δ18O and d-excess provides estimates of ice (65 ± 14%), snowpack (15 ± 9%) and fresh snow (20 ± 5%) contributions, respectively. Our field-based specific ablation measurements show that ice and snow melt contributions are 80 ± 16% and 20 ± 4%, respectively. The differences in hydrograph component estimates are apparently due to an unaccounted snow contribution ‘missing component’ from the valley slopes in field-based ablation measurements, whereas the isotope-based hydrograph separation method accounts for all the components, and provides a basin integrated estimate. Therefore, we suggest that for similar types of basins where contributions of rainfall and groundwater are minimal, and glaciers are often inaccessible for frequent field measurements/observations, the stable isotope-based method could significantly add to our ability to decipher moisture sources and estimate hydrograph components.
Highlights
The Himalayan-Karakorum mountain range has the largest concentration of glaciers outside the polar regions, out of which ~9600 glaciers lie in the Indian Himalayas, covering an area ofWater 2019, 11, 2242; doi:10.3390/w11112242 www.mdpi.com/journal/water~40,000 km2 [1]
The present study provides insights on the moisture sources for the precipitation and hydrograph components of the Sutri Dhaka Glacier basin in the western Himalayas during the peak ablation period in the year 2015
The major sources for the precipitation during summer are supplied by the Indian Summer Monsoon (ISM) as well as Western Disturbances (WDs)
Summary
The Himalayan-Karakorum mountain range has the largest concentration of glaciers outside the polar regions, out of which ~9600 glaciers lie in the Indian Himalayas, covering an area of. These glaciers are the perennial source of runoff to major river systems, such as the. These perennial rivers support more than a billion people living in the downstream region for their livelihood e.g., drinking, irrigation, industrial and sanitation [2,3,4,5]. Among all the major Himalayan river basins, the Indus Basin has the largest (~22,000 km2 ) glacier extent [3]. Previous studies have suggested that ~70% of Himalayan glaciers are receding at a faster rate, which has resulted in net loss of glacier volume [2,7,8]
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