Identifying and estimating the sources of river flow in the cold arid desert environment of Upper Indus River Basin (UIRB), western Himalayas

A reliable water supply in different Himalayan River basins is increasingly important for domestic, agriculture, and hydropower generation. These water resources are under serious threat due to climate change, with the potential to alter the economic stability of 237 million people living in the Indus River Basin alone. In the present study, we used new stable water isotope data set to identify and estimate the different sources of streamflow and their controlling factors in the Upper Indus River Basin (UIRB), India. The data set presented wide spatial and temporal variability without the distinct isotopic signature of various sources of river flow. However, variable but distinct signatures of sources of river/stream flow exist at the sub-basin or catchment scale. These variabilities are ascribed to changing physiographical, meteorological, and local climatic conditions. Further, the distinct microclimatic conditions including altitudinal variability, aspect slope, etc. govern the spatio-temporal variability of sources and streamflow, hence different lapse rates at sub-basin/catchment scale. The study suggested that the contribution of snowmelt and glacier melt to river flow varies spatially and temporally. The Bayesian mixing model results suggested that snowmelt contribution is higher in Indus (63 +/- 1.2%) and Shyok (58 +/- 1.7%) while as, glacier melt contribution is higher in Nubra 64 +/- 2.3% and Suru 60 +/- 2.7% sub-basins/catchments. The groundwater contribution (baseflow) sustains and regulates the flow in rivers/streams during winter and spring, which is very vital for the local water supply. The study suggests that the spatially diverse rugged topography and microclimate in UIRB dominantly control the differential contribution from various sources of river flow. The warming climate, which has resulted in a decrease in solid precipitation, continuous glacier mass loss, early melting of snow cover, etc., would have an inconsistent impact on the perennial flow of rivers with the potential to alter the economic and political stability in the region.

Automated summary

A reliable water supply in different Himalayan River basins is increasingly important. However, these water resources are under serious threat due to climate change. This study used stable water isotope data to identify and estimate the different sources of river flow in the Upper Indus River Basin in India.