Hydrograph apportionment of the Chandra River draining from a semi-arid region of the Upper Indus Basin, western Himalaya

Melting of snow and glaciers from the high-altitude Himalayan region is a significant water source to the major Himalayan rivers, especially in the upper Indus Basin (UIB), which contributes up to 70% of river discharge. Considering Indus Basin as a largest irrigation system dependent on snow and glacier melt runoff, it is imperative to study the rivers' current status and water budget. In this study we have performed a tracer-based hydrograph separation to quantify the contribution of seasonal snow, glacier melt, and groundwater to the Chandra River draining from a semi-arid region of the upper Indus basin, western Himalaya. Our study revealed a negligible control of summer (May-September 2017) precipitation and significant control of summer air temperature (May-September 2017) and winter precipitation over the Chandra River discharge, with 1 °C rise in air temperature leading to 22 m³s^-1 (15% of mean) increase in the river discharge (R² = 0.85; n = 541; p < 0.001). The hydrograph separation of the Chandra River suggests groundwater (38.3 ± 5.6%; 96.8 m³s^-1) as a significant source to the river runoff, followed by a direct contribution from glacier melt (30.9 ± 9%; 88.2 m³s^-1) and seasonal snowmelt (30.6 ± 5.7%; 84.2 m³s^-1), respectively, with negligible contribution from rainfall. Although groundwater is a significant contributor to the river runoff, the infiltration of seasonal snowmelt (54%) and glacier melt (46%) mostly contributed to the groundwater recharge. Present study establishes a linkage between seasonal snowmelt, glacier melt, groundwater, and the river runoff and would be useful to better model and predicts the future changes in the water resources of the upper Indus Basin.