Abstract
The Soil and Water Assessment Tool (SWAT) was used to simulate five glacierized river basins that are global in coverage and vary in climate. The river basins included the Narayani (Nepal), Vakhsh (Central Asia), Rhone (Switzerland), Mendoza (Central Andes, Argentina), and Central Dry Andes (Chile), with a total area of 85,000 km2. A modified SWAT snow algorithm was applied in order to consider spatial variation of associated snowmelt/accumulation by elevation band across each subbasin. In previous studies, melt rates varied as a function of elevation because of an air temperature gradient while the snow parameters were constant throughout the entire basin. A major improvement of the new snow algorithm is the separation of the glaciers from seasonal snow based on their characteristics. Two SWAT snow algorithms were evaluated in simulation of monthly runoff from the glaciered watersheds: (1) the snow parameters are lumped (constant throughout the entire basin) and (2) the snow parameters are spatially variable based on elevation bands of a subbasin (modified snow algorithm). Applying the distributed SWAT snow algorithm improved the model performance in simulation of monthly runoff with snow-glacial regime, so that mean RSR decreased to 0.49 from 0.55 and NSE increased to 0.75 from 0.69. Improvement of model performance was negligible in simulations of monthly runoff from the basins with a monsoon runoff regime.
Highlights
The two basic snowmelt approaches generally used in hydrologic modeling are energy balance models and temperature-index models [1]
Distributed, process-based energy budget models have been tested in Soil and Water Assessment Tool (SWAT), but we focused on another component of frequently used glacier/snowmelt models
The symbol “s” in the tables stands for glacier-free elevation bands or snowy elevation bands and “g” stands for glaciered elevation bands over the ELA0 altitudes
Summary
The two basic snowmelt approaches generally used in hydrologic modeling are energy balance models and temperature-index models [1]. In temperature-index based runoff models such as SWAT, melt rates only vary as a function of elevation, because of the air temperature gradient [5]. To overcome this drawback, a modified snow process was incorporated into SWAT in order to consider spatial variation of snowmelt/accumulation parameters by elevation band across subbasins. Previous studies using SWAT kept these parameters constant for an entire basin [6,7,8,9,10] While this method was successful in simulation of snowmelt flow, simulation of runoff from glaciered watersheds demands a distributed model for distinguishing seasonal snow from glacier. The new approach allows for the separation of seasonal snowmelt from glaciers’ melt based on the spatial variability of associated melt parameters
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