Modelling floods in the Ammer catchment: limitations and challenges with a coupled meteo-hydrological model approach

Abstract

Numerous applications of hydrological models have shown their capability to simulate hydrological processes with a reasonable degree of certainty. For flood modelling, the quality of precipitation data the key input parameter is very important but often remains questionable. This paper presents a critical review of experience in the EU-funded RAPHAEL project. Different meteorological data sources were evaluated to assess their applicability for flood modelling and forecasting in the Bavarian pre-alpine catchment of the Ammer river (709 km²), for which the hydrological aspects of runoff production are described as well as the complex nature of floods. Apart from conventional rain gauge data, forecasts from several Numerical Weather Prediction Models (NWP) as well as rain radar data are examined, scaled and applied within the framework of a GIS-structured and physically based hydrological model. Multi-scenario results are compared and analysed. The synergetic approach leads to promising results under certain meteorological conditions but emphasises various drawbacks. At present, NWPs are the only source of rainfall forecasts (up to 96 hours) with large spatial coverage and high temporal resolution. On the other hand, the coarse spatial resolution of NWP grids cannot yet address, adequately, the heterogeneous structures of orographic rainfields in complex convective situations; hence, a major downscaling problem for mountain catchment applications is introduced. As shown for two selected Ammer flood events, a high variability in prediction accuracy has still to be accepted at present. Sensitivity analysis of both meteo-data input and hydrological model performance in terms of process description are discussed, drawing positive conclusions for future applications of an advanced meteo-hydro model synergy.

Verification of operational Quantitative Discharge Forecast (QDF) for a regional warning system – the AMPHORE case studies in the upper Po River

“…Nevertheless, when the lag time is very short, to extend the lead-time between warning and flood event, a rainfall predictor is required (Lardet and Obled, 1994;Brath et al, 1988). Starting from the pioneering work of Georgakakos and Hudlow (1984), meteorological models are often coupled with hydrological simulations (Jasper et al, 2002;Montaldo et al, 2002;Ludwig et al, 2003). While this chaining allows floods to be forecasted on small catchments with response times ranging from 6 to 12 h it, however, causes new problems for the reliability of Quantitative Precipitation Forecasts (QPF) and also creates additional accuracy problems for space and time scales.…”

Perturbation of convection-permitting NWP forecasts for flash-flood ensemble forecasting

“…Multi-model approaches (Jasper et al, 2002;Ludwig et al, 2003;Komma et al, 2007) can avoid the numerical cost issue but it is sometimes difficult to find a good overlapping domain. Other numerically cheap methods produce probabilistic precipitation forecasts from single-value model outputs.…”

“…Several works aim at downscaling the Ensemble Prediction System (EPS) forecast (Molteni et al, 1996) of the ECMWF (European Centre for Mediumrange Weather Forecasts). Diomede et al (2006) performed a 10-km resolution dynamical downscaling of "representative members" selected from a clustering of the ECMWF EPS (COSMO-LEPS, Marsigli et al, 2005). Ferraris et al (2002) added a multifractal disaggregation of the LEPS members to cope with the smaller Mediterranean watersheds.…”

Effects of data resolution and stream delineation threshold area on the results of a kinematic wave based GIUH model

“…The introduction of SRTM DEMs, for all parts of the world, ended hydrologists' long wait for DEMs with an acceptable accuracy and resolution (Ludwig et al, 2006). The SRTM DEMs resolution is 30 m for the USA and 90 m for other countries.…”