Multi‐scale modelling of land‐use change and river training effects on floods in the Rhine basin

Land-use changes effects on floods are investigated by a multi-scale modelling study, where runoff generation in catchments of different sizes, different land uses and morphological characteristics are simulated in a nested manner. The macro-scale covers the Rhine basin (excluding the alpine part), the upper meso-scale covers various tributaries of the Rhine and three lower meso-scale study areas (100–500 km 2 ) represent different characteristic land-use patterns. The main innovation is the combination of models at different scales and at different levels of process representation in order to account for the complexity of land-use change impacts for a large river basin. The results showed that the influence of land-use on storm runoff generation is stronger for convective storm events with high precipitation intensities than for long advective storms with low intensities. The simulated flood increase at the lower meso-scale for a scenario of rather strong urbanization is in the order of 0 and 4% for advective rainfall events, and 10–30% for convective rain storms with a return period of 2–10 years. Convective storm events, however, are of hardly any relevance for the formation of floods in the large river basins of Central Europe, because the extent of convective rainstorms is restricted to local occurrence. Due to the dominance of advective precipitation for macro-scale flooding, limited water retention capacity of antecedent wet soils and superposition of flood waves from different tributaries, the land-use change effects at the macro-scale are even smaller, for example at Cologne (catchment area 100 000 km 2 ), land-use change effects may result in not more than 1–5 cm water level of the Rhine. Water retention measures in polders along the Upper and Lower Rhine yield flood peak attenuation along the Rhine all the way down to the Dutch border between 1 and 15 cm. Copyright # 2007 John Wiley & Sons, Ltd.