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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 10 | Copyright
Nat. Hazards Earth Syst. Sci., 18, 2653-2674, 2018
https://doi.org/10.5194/nhess-18-2653-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Oct 2018

Research article | 18 Oct 2018

Convection-permitting regional climate simulations for representing floods in small- and medium-sized catchments in the Eastern Alps

Christian Reszler1, Matthew Blaise Switanek2, and Heimo Truhetz2 Christian Reszler et al.
  • 1JR-AquaConSol GmbH, Steyrergasse 21, 8010 Graz, Austria
  • 2Wegener Center for Climate and Global Change, University of Graz, 8010 Graz, Austria

Abstract. Small-scale floods are a consequence of high precipitation rates in small areas that can occur along frontal activity and convective storms. This situation is expected to become more severe due to a warming climate, when single precipitation events resulting from deep convection become more intense (super Clausius–Clapeyron effect). Regional climate model (RCM) evaluations and inter-comparisons have shown that there is evidence that an increase in RCM resolution and, in particular, at the convection-permitting scale will lead to a better representation of the spatial and temporal characteristics of heavy precipitation at small and medium scales. In this paper, the benefits of grid size reduction and bias correction in climate models are evaluated in their ability to properly represent flood generation in small- and medium-sized catchments. The climate models are sequentially coupled with a distributed hydrological model. The study area is the Eastern Alps, where small-scale storms often occur along with heterogeneous rainfall distributions leading to a very local flash flood generation. The work is carried out in a small multi-model framework using two different RCMs (CCLM and WRF) in different grid sizes. Bias correction is performed by the use of the novel scaled distribution mapping (SDM), which is similar to the usual quantile mapping (QM) method. The results show that, in the investigated RCM ensemble, no clear added value of the usage of convection-permitting RCMs for the purpose of flood modelling can be found. This is based on the fact that flood events are the consequence of an interplay between the total precipitation amount per event and the temporal distribution of rainfall intensities on a sub-daily scale. The RCM ensemble is lacking in one and/or the other. In the small catchment ( < 100km2), a favourable superposition of the errors leads to seemingly good CCLM 3km results both for flood statistics and seasonal occurrence. This is, however, not systematic across the catchments. The applied bias correction only corrects total event rainfall amounts in an attempt to reduce systematic errors on a seasonal basis. It does not account for errors in the temporal dynamics and deteriorates the results in the small catchment. Therefore, it cannot be recommended for flood modelling.

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Small-scale floods are a consequence of high rainfall rates in small areas that can occur along frontal activity and convective storms. This situation is expected to become more severe due to a warming climate. This study shows the test of fine-gridded (~ 3 km spacing) climate models combined with error-correction techniques for flood modelling in small- and medium-sized catchments. Results are promising, but further research is needed so these models can be applied in climate change studies.
Small-scale floods are a consequence of high rainfall rates in small areas that can occur along...
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