Impact of climate change on hydrological regimes and water resources management in the rhine basin

The International Commission for the Hydrology of the Rhine basin (CHR) has carried out a research project to assess the impact of climate change on t he river flow conditions in the Rhine basin. Along a bottom-up line, differ ent detailed hydrological models with hourly and daily time steps have been developed for representative sub-catchments of the Rhine basin. Along a to p-down line, a water balance model for the entire Rhine basin has been deve loped, which calculates monthly discharges and which was tested on the scal e of the major tributaries of the Rhine. Using this set of models, the effe cts of climate change on the discharge regime in different parts of the Rhi ne basin were calculated using the results of UKHI and XCCC GCM-experiments . All models indicate the same trends in the changes: higher winter dischar ge as a result of intensified snow-melt and increased winter precipitation, and lower summer discharge due to the reduced winter snow storage and an i ncrease of evapotranspiration. When the results are considered in more deta il, however, several differences show up. These can firstly be attributed t o different physical characteristics of the studied areas, but different sp atial and temporal scales used in the modelling and different representatio ns of several hydrological processes (e.g., evapotranspiration, snow melt) are responsible for the differences found as well. Climate change can affec t various socio-economic sectors. Higher temperatures may threaten winter t ourism in the lower winter sport areas. The hydrological changes will incre ase flood risk during winter, whilst low flows during summer will adversely affect inland navigation, and reduce water availability for agriculture an d industry. Balancing the required actions against economic cost and the ex isting uncertainties in the climate change scenarios, a policy of 'no-regre t and flexibility' in water management planning and design is recommended, where anticipatory adaptive measures in response to climate change impacts are undertaken in combination with ongoing activities.