Abstract
Flood projections are still highly uncertain, partly resulting from the limited accuracy of simulated precipitation by climate models. To overcome this limitation, recent studies suggest to use direct linkages between atmospheric processes leading precipitation, often better simulated than precipitation, and the flood occurrence. Such an approach implies, however, that historical flood events mainly result from direct contribution of precipitation only. Consequently, this paper has a twofold objective: (i) To explore to what extent the generation of medium-magnitude flood events in a large mountainous catchment can be explained by the precipitation only, and (ii) to identify what are the best features of flood-inducing precipitation episodes (i.e., duration and accumulation). Taking advantage of centennial-long discharge (gauge stations) and precipitation (ERA-20C reanalysis) data series, this study is based on three-year return period flood events of the upper Rhône River (NW European Alps). Our results suggest that half of the studied floods are triggered by precipitation only, but precipitation indices are mainly good only for high-magnitude events with return period of at least 20 years. Hence, modelling flood occurrence directly from atmospheric processes leading precipitation seems to be possible for events with the highest magnitude (i.e., the ones with the highest potential to impact societies).
Highlights
Exploring future flood hazard variability is generally accomplished by coupling atmospheric climate projections with land-surface schemes and hydrological models [1]
The use of atmospheric indicators to estimate future changes in floods occurrence relies on two main assumptions: (i) historical flood events mainly result from particular “extreme” precipitation accumulation, and that (ii) these extreme precipitation episodes are associated to particular atmospheric features that could be used as predictors from climate projections [9,11]
In line with the literature on flood typologies of Alpine rivers, our results suggest two main groups of flood types occur on the upper Rhône River: (i) types 1 and 2 for which direct accumulation of precipitation is the main trigger of three-year return period flood events, and (ii) types 3 and 4 for which such floods result from a combination of precipitation as well as others processes
Summary
Exploring future flood hazard variability is generally accomplished by coupling atmospheric climate projections with land-surface schemes and hydrological models [1]. This practice leads to high uncertainty in the evolution of the flood magnitude and frequency, mainly due to (i) the uncertainties of extreme precipitation projections provided by global and/or regional climate models [2,3,4,5], and (ii) the uncertainties resulting from the hydrological modelling [6,7]. The use of atmospheric indicators to estimate future changes in floods occurrence relies on two main assumptions: (i) historical flood events mainly result from particular “extreme” precipitation accumulation, and that (ii) these extreme precipitation episodes are associated to particular atmospheric features that could be used as predictors from climate projections [9,11]
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