Simulating one century (1902–2009) of river discharges, low flow sequences and flood events of an alpine river from large-scale atmospheric information
Abstract. We assess the ability of two typical simulation chains to reproduce, over the last century (1902–2009) and from large-scale atmospheric information only, the temporal variations of river discharges, low flow sequences and flood events, observed at different locations of the Upper Rhône River (URR) catchment, an alpine river straddling France and Switzerland (10,900 km2). The two simulation chains are made up of a downscaling model, either statistical (SCAMP) or dynamical (MAR), and the glacio-hydrological model GSM-SOCONT. Both downscaling models, forced by atmospheric information from the ERA-20C atmospheric reanalysis, provide time series of daily scenarios of precipitation and temperature used as input to the hydrological model. With hydrological regimes ranging from highly glaciated ones in its upper part to mixed ones dominated by snow and rain downstream, the URR catchment is ideal to evaluate the different simulation chains in contrasting and demanding hydro-meteorological configurations where the interplay between weather variables, both in space and time, is determinant. Whatever the river sub-basin considered, the simulated discharges are in good agreement with the reference ones, provided that the weather scenarios are bias-corrected. The observed multi-scale variations of discharges (daily, seasonal and interannual) are well reproduced and the hydrological situations of low frequency (low flow sequences and flood events) are reasonably well reproduced. Bias correction is crucial for both precipitation and temperature and both downscaling models. For the dynamical one, a bias correction is also essential to get realistic daily temperature lapse rates. Uncorrected scenarios lead to irrelevant hydrological simulations, especially for the sub-catchments at high elevation, mainly due to irrelevant snowpack dynamic simulations. The simulations also highlight the difficulty to simulate precipitation dependency to elevation over mountainous areas.
