Spatial and meteorological controls of stable water isotope dynamics of precipitation in Kashmir Valley, Western Himalaya, India.

In the Himalayas, the lives and livelihoods of millions of people are sustained by water resources primarily depending on the moisture brought by Western Disturbances and Indian Summer Monsoon. In the present study, a network of 12 precipitation stations was established across the Kashmir Valley to understand the spatial and meteorological factors controlling precipitation isotopes. Temperature and relative humidity are dominant meteorological factors, whereas altitude, proximity to forest canopy, land use/land cover, windward and leeward sides of the mountains are the main physical factors influencing precipitation isotopes. The study suggests that the Mediterranean Sea and nearby water bodies along with continental recycling are the dominant sources of moisture from October to May, while the Arabian Sea, Bay of Bengal and continental recycling are the main sources of moisture from June to September. However, some precipitation events from October to May collect moisture from the Arabian Sea and some precipitation events from June to September collect moisture from the Mediterranean Sea. The occasional passage of Western Disturbances in summer merging with the Indian Summer Monsoon yields heavy to very heavy precipitation. The study provides a better understanding of complex spatial and meteorological phenomena controlling precipitation isotopes across the Western Himalayas.

Impact of Indian summer monsoon in westerly dominated water resources of western Himalayas.

We used stable water isotopes of oxygen and hydrogen to identify and estimate the seasonal contribution of precipitation to the regional hydrology of Sindh and Rambiara catchments of western Himalayas. The different source waters exhibit significant spatio-temporal variations that correspond to the change in seasonal meteorology, precipitation form and moisture sources. The two-component hydrograph separation based on d-excess suggests that the western disturbances (WD) contribute dominantly (76 ± 4 %) to the regional hydrology, compared to Indian summer monsoon (ISM) rainfall (24 ± 4 %). A comparison of d-excess values of WD and ISM indicates the groundwater consists of 90 ± 3 % WD sources and 10 ± 2 % ISM sources, signifying distinct seasonal variations in groundwater recharge sources. The sine wave model results showed that the annual mean residence time (MRT) of groundwater for the Sindh catchment (5.8 ± 0.6 months) is greater than the Rambiara groundwater (3.6 ± 0.5 months). The lower isotope values observed in the river water than in the precipitation suggest its origin from the snowmelt. This study provides valuable insights into the hydrological processes operating in the high altitude Himalayan catchments to facilitate the improved understanding of runoff generation mechanisms and water resource management in future climate change scenarios.

Hydrochemical assessment (major ions and Hg) of meltwater in high altitude glacierized Himalayan catchment.

Snowpack and glacial melt samples were collected to understand the hydrochemical, isotopic characteristics and the source of Hg contamination in high altitude glacierized Himalayan catchment. Both the snow and glacial melt were acidic in nature with calcium and magnesium as the dominant cations and bicarbonate and chloride as the dominant anions. The major ion concentrations for cations were found to be Ca2+ > Mg2+ > Na+ > K+ and HCO3- > Cl- > SO42- > NO3- for anions. The atmospheric processes like the precipitation source and aerosol scavenging control the snow chemistry and the weathering of the rocks modify the hydrochemistry of glacial melt. The samples of both the snow and glacial melt were classified as Ca-Mg-HCO3- type. The concentration of Hg in snow (154.95 ng L-1) and glacial melt (112.04 ng L-1) was highest (still lower compared to the maximum permissible limit (1000 ng L-1) by WHO in drinking water) during summer season (August-September) and lowest (snow 2.2 and 40.01 ng L-1 for glacial melt) during winter (November). The results reveal that mercury concentration in snowpacks is attributed to the combined mixing of long-range transport of pollutants via westerlies throughout the year and the industrial effluents coming from highly industrial belts of Panjab, Haryana, Rajasthan, Indo-Gangetic plains, and neighboring areas via southwest monsoons during August-September. However, in glacial melt, the Hg concentration was typically controlled by rate of melting, leaching, and percolation. Higher degree and rate of glacial melting decreases the Hg concentration in glacial melt. Stable isotopic analysis and backward air mass trajectory modeling also corroborate the source of precipitation from southwest monsoons during August-September, with its air mass trajectories passing through the highly industrialized belts of Indo-Gangetic plain and adjoining areas.