Comparison and evaluation of regional climate scenarios for hydrological impact analysis: General scheme and application example

We present a scheme and application example for evaluating simulations of possible future conditions of regional climate ('regional climate change scenarios') concerning their suitability for hydrological impact studies. The procedure is based on expert knowledge about the impacts of anthropogenic climate change on varying hydrological processes and different hydrological catchment status. A method to evaluate regional climate change scenarios for hydrological impact analysis is presented first, which consists basically of a two-step knowledge-based decision and evaluation procedure. The first step ('climatic evaluation') evaluates the capability of the climate scenarios to represent regional climate and the plausibility of the future climate conditions. The first step establishes the basis for the second step ('hydrological evaluation'), which evaluates hydrologically relevant information of the climate scenarios to qualify information about the hydrological processes possibly altered by climate change. From this evaluation of the hydrological processes, an evaluation of regional catchment conditions is derived, such as long-term water availability, drought conditions or floods. In the second part of the paper, this method is applied systematically to three different regional climate change scenarios, which have been provided for south Germany. This evaluation results in different levels of adequacy, depending on the hydrological process under question. In general, processes which are governed by temperature conditions (e.g. evaporation, snowmelt) are evaluated as 'more useful' than the processes governed by precipitation characteristics (e.g. runoff generation, floods). All regional climate change scenario methods investigated are of rather limited value for extreme hydrological conditions. The proposed method can serve to systematically evaluate the usefulness of climate change scenarios for hydrological impact analysis. It becomes apparent that regional climate scenarios should only be applied for hydrological application if the spatial-temporal scale of variations of the governing hydrological processes is represented by the scenarios. Copyright (C) 2007 Royal Meteorological Society