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A general increase in precipitation has been observed in Germany in the last century, and potential changes in flood generation and intensity are now at the focus of interest. The aim of the paper is twofold: a) to project the future flood conditions in Germany accounting for various river regimes (from pluvial to nival-pluvial regimes) and under different climate scenarios (the high, A2, low, B1, and medium, A1B, emission scenarios) and b) to investigate sources of uncertainty generated by climate input data and regional climate models. Data of two dynamical Regional Climate Models (RCMs), REMO (REgional Model) and CCLM (Cosmo-Climate Local Model), and one statistical-empirical RCM, Wettreg (Wetterlagenbasierte Regionalisierungsmethode: weather-type based regionalization method), were applied to drive the eco-hydrological model SWIM (Soil and Water Integrated Model), which was previously validated for 15 gauges in Germany. At most of the gauges, the 95 and 99 percentiles of the simulated discharge using SWIM with observed climate data had a good agreement with the observed discharge for 1961-2000 (deviation within +/- 10 %). However, the simulated discharge had a bias when using RCM climate as input for the same period. Generalized Extreme Value (GEV) distributions were fitted to the annual maximum series of river runoff for each realization for the control and scenario periods, and the changes in flood generation over the whole simulation time were analyzed. The 50-year flood values estimated for two scenario periods (2021-2060, 2061-2100) were compared to the ones derived from the control period using the same climate models. The results driven by the statistical-empirical model show a declining trend in the flood level for most rivers, and under all climate scenarios. The simulations driven by dynamical models give various change directions depending on region, scenario and time period. The uncertainty in estimating high flows and, in particular, extreme floods remains high, due to differences in regional climate models, emission scenarios and multi-realizations generated by RCMs.
Wetlands, and in particular riparian wetlands, represent an interface between the catchment area and the aquatic environment. They control the exchange of water and related chemical fluxes from the upper catchment area to surface waters like streams and lakes. Their influence on water and nutrient balances has been investigated mainly at the patch scale. In this study an attempt was made (a) to integrate riparian zones and wetlands into eco-hydrological river basin modelling, and (b) to quantify the impacts of riparian wetland processes on water and nutrient fluxes in a meso-scale catchment located in the northeastern German lowland. The investigation was performed by analysing hydro-chemical field data and applying the eco-hydrological model SWIM (Soil and Water Integrated Model), which was extended to reproduce the relevant water and nutrient flows and retention processes at the catchment scale in general, and in riparian zones and wetlands in particular. The main extensions introduced in the model were: (1) implementation of daily groundwater table dynamics at the hydrotope level, (2) implementation of water and nutrient uptake by plants from groundwater in riparian zones and wetlands, and (3) assessment of nutrient retention in groundwater and interflow. The simulation results indicate that wetlands, though they represent relatively small parts of the total catchment area, may have a significant impact on the overall water and nutrient balances of the catchment. The uncertainty of the simulation results is considerably high, with the main sources of uncertainty being the model parameters representing the geo-hydrology and the input data for land use management. (c) 2006 Elsevier B.V. All rights reserved.