A Model Setup for Mapping Snow Conditions in High-Mountain Himalaya

Abstract

Seasonal snow cover is an important source of melt water for irrigation and hydropower production in many regions of the world, but can also be a cause of disasters, such as avalanches and floods. In the remote Himalayan environment there is a great demand for up-to-date information on the snow conditions for the purposes of planned hydropower development and disaster risk reduction initiatives. We describe and evaluate a snow mapping setup for the remote Langtang Valley in the Nepal Himalayas, which can deliver data for snow and water availability mapping all year round. The setup utilizes (1) robust and almost maintenance-free in-situ instrumentation with satellite transmission, (2) a freely available numerical snow model, and (3) estimation of model key parameters from local meteorological and snow observations as well as from freely available climatological data. Novel features in the model include the estimation of melt parameters and solid precipitation from passive gamma-radiation based snow sensor data, as well as improved parameterization and estimation of melt water refreezing (36% of total melt) within, and sublimation/evaporation (57 mm yr −1 ) from the snow pack. Evaluation of the model results show a reasonable fit with snow cover data from satellite images. As many of the high-mountain regions in central and eastern Nepal show high correlation (>0.8) with the estimated snow line elevation in the Langtang catchment, the results may provide a first-order approximation of the snow conditions for these areas too.

Near Real-Time Measurement of Snow Water Equivalent in the Nepal Himalayas

“…Relatively high average sublimation rates of 1.0 mm w.e. per day, or 21% of annual snowfall, have been reported for the nearby Yala Glacier in the Langtang Catchment (Stigter et al, 2018) and Saloranta et al (2019) report that sublimation accounts for 17% of all SWE losses at Ganja La. The importance of sublimation as a process in high-altitude environments demonstrates the value of applying a dedicated SWE sensor, along with complementary meteorological instruments, that can distinguish SWE losses from redistribution within the footprint of the sensor and quantify the loss of SWE under different meteorological conditions.…”

“…The transmission of data using the Iridium satellite constellation is a robust and convenient method for achieving near-real time monitoring of snow conditions in high mountain environments. Variables measured and transmitted using this technique can be used to force near-real time simulations of the timing and magnitude of snowmelt into the catchment hydrological system and forecast avalanche risk (Saloranta et al, 2019). In order for these efforts to be worthwhile in the long term, the setup should require minimal maintenance whilst providing representative estimates of their measured variables of interest.…”

“…The majority of snow cover in the Langtang catchment is less than 600 mm w.e. (Stigter et al, 2017;Saloranta et al, 2019). Locations where SWE exceeds 600 mm w.e.…”

“…Previous research has demonstrated that this region is characterized by significant and seasonally varying gradients of precipitation and temperature which need to be considered when attempting to spatially distribute automatic weather station measurements over a larger spatial scale (Immerzeel et al, 2014). If several stations, similar to the automatic weather station presented here, were installed along an elevational transect, precipitation and temperature gradients could be estimated in near real-time across a catchment, permitting snow properties to be modeled and estimated at the catchment scale or beyond (Saloranta et al, 2019). When combined with a reliable satellite-based transmission service, this instrument setup is capable of delivering valuable near real-time information about seasonal water resources stored as snow in high-altitude locations.…”

“…Many communities, particularly those at high elevations, are dependent on seasonal snowmelt for water, hydropower generation and irrigation (Smith T. et al, 2017), whilst changes in snow conditions and extent have major ramifications for ecosystem function, avalanche threat, and climate feedbacks such as land surface albedo (Lehning et al, 1999;Sturm et al, 2010;Rohrer et al, 2013). With ongoing climate change predicted to affect the high-altitude Himalayan cryosphere (e.g., Singh and Kumar, 1997;Singh and Bengtsson, 2005;Stewart, 2009;Kraaijenbrink et al, 2017;Smith and Bookhagen, 2018), it is critical that seasonal Himalayan snowpacks are comprehensively monitored to facilitate the development of hydrological models that can be used to forecast water availability in this region (López-Moreno et al, 2013;Sexstone and Fassnacht, 2014;Saloranta et al, 2019).…”