Berg, P.

Duethmann, D.

Feldmann, H.

Ihringer, J.

Kunstmann, H.

Liebert, J.

Merz, B.

Ott, I.

Schädler, G.

Wagner, S.

English

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Helmholtz Climate Initiative Regional Climate Change Topic 6: Extreme events - How will the magnitude and frequency of        extreme weather events change in a future climate?  www.reklim.de An ensemble assessment of the climate change impact on flood hazard  for three small to medium sized catchments in Germany Introduction Figure 3 Left : Simulated MHQ for the control period 1971-2000 with climate input  from observations (SimObs) and the RCMs. Right : Percentage  change of MHQ between the scenario (2021-2050) and control (1971-2000) period. The gray shaded areas mark the range of the individual model projections. D. Duethmann1, I. Ott2; J. Liebert3; P. Berg4; H. Feldmann4; J. Ihringer3; H. Kunstmann2; B. Merz1; G. Schaedler4; S. Wagner2  (1) GFZ, Potsdam, Germany (2) IMK-IFU, KIT, Garmisch-Partenkirchen, Germany (3) IWG, KIT, Karlsruhe, Germany (4) IMK-TRO, KIT, Karlsruhe, Germany.  Figure 4: Changes in discharge for given return periods. Values are based on the change of the 2*30 maximum annual, summer (SH) or winter (WH) values for the period 2021-2050 versus 1971-2000. R1-3: Realizations of ECHAM5. The gray shaded areas mark the maximum range of the single ensemble members. One color implies both HMs. • Aim: quantification of the climate change impact on changes in flood discharges for the near future.            Important for the adaptation of flood management. • Scenario assessments based on only one combination of global climate model (GCM), regional climate model (RCM)  and hydrological model (HM) might be misleading.           Ensemble approach: based on 2 GCMs, 2 high-resolution RCMs (7km) and 3 HMs. Results Methods: study area, climate input, hydrological models Conclusions Study area: Selection of three catchments representing different flood regimes in Germany: Ruhr (4485 km², winter floods), Mulde (6171 km², floods in winter/spring, but also in summer), Ammer (710 km², summer floods).  Projected changes in meteorological input:  • Temperature: shows an increase (on average +1.1 C, range 0.8-1.5 C) in all catchments and for all ensemble members. • Precipitation:  Only in the Ruhr catchment all ensemble members project a change in the same direction. In the other two catchments, the ensemble mean indicates an increase, but some ensemble members show decreases. • The ten member ensemble based on 2 GCMs, 2 high-resolution RCMs and 2 HMs demonstrates large uncertainties for the possible impact of climate change on flood hazard in the near future.  • Largest contributions to the overall uncertainty are from the different RCMs in the summer half year, and the different GCMs and their realizations in the winter half year. • Implications: water infrastructure needs to be planned and designed with these uncertainties, for example by planning water infrastructure in an adaptable way. Hydrological modeling results control period:  • Despite bias correction of temperature and precipitation, there are still some deviations between simulations with observed climate input and climate input from the RCMs (Fig. 3, left column). • Caused by: - differences in the precipitation data sets used as model input and for bias correction                     - deviations in climate variables which are not bias corrected (radiation and humidity). Hydrological modeling results scenario period:  • Large spread of changes in mean monthly maximum discharges and return values in all three catchments (Fig. 3+4, gray area).  • Ammer: the ensemble mean indicates a change in the seasonality with higher flood discharges in winter and lower flood discharges in summer (Fig. 3+4, top row).  • Mulde: no overall trend towards increasing or decreasing flood discharges can be observed (Fig. 3+4, middle row).  • Ruhr : the changes in mean monthly maximum discharge and return values, suggest increasing flood probabilities  (Fig. 3+4, bottom row).  Figure 1: Locations of the three selected catchments. Figure 2: The ensemble approach. Ensemble:  • Emission scenario: A1B; only one scenario, as other projects already showed that the emission scenario has only a smaller impact  for the near future (2021-2050). • GCMs: The climate projections are based on three realizations of ECHAM5 and one realization of CCCma3.  • RCMs: All GCM simulations are downscaled by the RCM CLM, and one realization of ECHAM5 is downscaled also with the RCM WRF. • HMs: In each of the catchments two of three selected HMs (PRMS, SWIM and WaSiMETH) are applied. 

An ensemble assessment of the climate change impact on flood hazard for three small to medium sized catchments in Germany

https://publikationen.bibliothek.kit.edu/220087769/3816112

An ensemble assessment of the climate change impact on flood hazard for three small to medium sized catchments in Germany

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