Abstract
This study compares the ability of two degree-day models (Poli-Hydro and a degree-day implementation of Alpine3D) and one full energy-balance melt model (Alpine3D) to predict the discharge on two partly glacierized Alpine catchments of different size and intensity of exploitation, under present conditions and climate change as projected at the end of the century. For present climate, the magnitude of snow melt predicted by Poli-Hydro is sensibly lower than the one predicted by the other melt schemes, and the melting season is delayed by one month. This difference can be explained by the combined effect of the reduced complexity of the melting scheme and the reduced computational temporal resolution. The degree-day implementation of Alpine3D reproduces a melt season closer to the one obtained with its full solver; in fact, the onset of the degree-day mode still depends upon the full energy-balance solver, thus not bringing any particular benefit in terms of inputs and computational load, unlike with Poli-Hydro. Under climate change conditions, Alpine3D is more sensitive than Poli-Hydro, reproducing discharge curves and volumes shifted by one month earlier as a consequence of the earlier onset of snow melt. Despite their benefits, the coarser temporal computational resolution and the fixed monthly degree-days of simpler melt models like Poli-Hydro make them controversial to use for climate change applications with respect to energy-balance ones. Nevertheless, under strong river regulation, the influence of calibration might even overshadow the benefits of a full energy-balance scheme.
Highlights
The hydrology of high Alpine catchments is dominated by the melt of seasonal snow cover and glaciers, and sensitive to climate change (Barnett et al, 2005)
This study showed that an energy-balance melt scheme can outperform a degree-day approach in the representation of the correct melt 30 dynamics, if the former is carefully fed with solid input data sets which are truly representative for the catchment
The two catchments, Mera and Dischma, are different in size and extent of water resources exploitation. Both the full energy balance and the degree-day versions of A3D outperform PH in reproducing the melt dynamics, especially over the almost-natural, nivo-glacial Dischma catchment, where snow melt is severely underestimated by PH
Summary
The hydrology of high Alpine catchments is dominated by the melt of seasonal snow cover and glaciers, and sensitive to climate change (Barnett et al, 2005). The development of models reproducing reliable predictions of the response of Alpine catchments discharge to climate change is a crucial step Both degree-day and energy-balance melt models have been implemented to simulate runoff in Alpine catchments (Huss et al, 2008; Bavay et al, 2009; Magnusson et al, 2011; Zhang et al, 2012; Farinotti et al, 2012; Gallice et al, 2016). When considering climate change, the use of such models may be disputable since the value of the calibrated parameters required by this type of models may change under different climatic conditions (Hock, 2005; Magnusson et al, 2010) This is relevant for (partly) glacierized catchments, as models have to deal with snow and ice melt under global warming and varying glacier surface. Land use and 10 weather conditions are highly diverse within any Alpine context and may as well experience future evolution as a consequence of rising temperatures
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