Abstract. In this study, we investigated the application and the
transferability of the Soil Water and Assessment Tool (SWAT) in a partly
glacierized Alpine catchment characterized by extreme climatic conditions
and steep terrain. The model was initially calibrated for the 10 km2
watershed of the Damma glacier Critical Zone Observatory (CZO) in central
Switzerland using monitoring data for the period of 2009–2011 and then was
evaluated for 2012–2013 in the same area. Model performance was found to be
satisfactory against both the Nash–Sutcliffe criterion (NS) and a benchmark
efficiency (BE). The transferability of the model was assessed by using the
parameters calibrated on the small watershed and applying the model to the
approximately 100 km2 catchment that drains into the hydropower
reservoir of the Göscheneralpsee and includes the Damma glacier CZO.
Model results were compared to the reservoir inflow data from 1997 to 2010
and it was found that the model predicted successfully snowmelt timing and
autumn recession but could not accurately capture the peak flow for certain
years. Runoff was slightly overestimated from late May to June, when it is
dominated by snowmelt. Finally, we investigated the response of the greater
catchment to climate change using three different climate change scenarios,
and the results were compared to those of a previous study, where two
different hydrological models, PREVAH and ALPINE3D, were used. The
methodology presented here, where SWAT is calibrated for a small watershed
and then applied for a bigger area with similar climatic conditions and
geographical characteristics, could work even under extreme conditions like
ours. However, greater attention should be given to the differences
between glacier melt and snowmelt dynamics. In conclusion, this assessment
test on the transferability of SWAT on different scales gave valuable
information about the strengths and weaknesses of the model when it was
applied under conditions different to those under which it was calibrated.
Abstract. In this study, we investigated the application of the Soil Water and Assessment Tool (SWAT) for the simulation of runoff in the partly glacierised watershed of the Damma glacier Critical Zone Observatory (CZO), Switzerland. The model was calibrated using daily time steps for the period of 2009–2011, while two different approaches were used for its validation. Initially the model was validated using daily data for the years 2012–2013. Subsequently, the calibrated version of the model was applied on the greater area that drains to the hydropower reservoir of the Göscheneralpsee and includes the Damma glacier watershed, using inflow data. This validation approach can help in assessing model uncertainty under changing land use and climate forcing. Model performance was evaluated both visually and statistically and it was found that even though SWAT has rarely been used in high alpine and glacierised areas and despite the complexity of simulating the extreme conditions of Damma glacier watershed; its performance was very satisfactory. Our novel validation approach proved to be successful since the performance of the model was similarly good when applied for the greater catchment feeding Göscheneralpsee. Finally, we investigated the response of the two regions, Damma glacier and its greater area, to climate change using SWAT and results were compared to a previous study using the models PREVAH and ALPINE 3D. It confirmed that SWAT can predict changes in future runoff and peak flow in alpine areas with the same accuracy as more demanding models such as ALPINE 3D and PREVAH. This study demonstrates the applicability of SWAT in high elevation, snow and glacier dominated watersheds and in quantifying the effects of climate change on water resources.
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