Comparing and contrasting the hydrology of high-elevation areas in the Rockies and the Himalayas

In 2009 Kathmandu University initiated a collaboration with the Niwot Ridge LTER program to begin studying climate change and water resources in high-elevation areas.  Water stored as ice and snow at high elevations is a resource that plays an important role in the hydrologic cycle, particularly in the timing and volume of downstream discharge.  In order to gain a better understanding of the impacts of climate change on water resources, it is first necessary to improve quantification of where river discharge comes from.  The vulnerability of the cryosphere to warming temperature trends underscores the need for work on estimating the volumes of ice and snow that move down from mountains as melt water.  One physically-based approach for estimating the contribution of various sources to streamflow is the collection of surface water and source water samples for isotopic analysis, where differences in isotopic values for various sources are compared to river water values.  This study uses oxygen-18 (δ¹⁸O) and deuterium (δ²H) isotope analyses to approximate relative contributions of different water sources to discharge in two high elevation basins.  River water samples collected between 1400 and 3745 meters in the Langtang Valley of central Nepal’s Himalayan Mountains in May and June 2012 are compared to Langtang Valley samples collected in December 2008 to examine seasonal variations.  Samples of source waters, including glacier melt and groundwater, are also compared between the two years.  The trend of decreasing δ¹⁸O (more depleted) in river water with higher elevation in Langtang, and the range of δ¹⁸O and δ²H values found in the river and source water samples from Langtang are also compared with a similar elevational gradient data set from the Niwot Ridge LTER site in the Colorado Rockies.  Niwot Ridge headwaters are around 3600m and the catchment also contains permanent ice and snowfields.  The unique isotopic chemistry of the different source waters in both of these study areas allows for confident estimation of glacier melt, snow melt, precipitation, and groundwater contributions to discharge.