Climate change scenarios and runoff response in the Mulde catchment (Southern Elbe, Germany) L. Menzel * , G. Bu ¨rger Potsdam Institute for Climate Impact Research (PIK), P.O. Box 601203, Telegrafenberg, 14412 Potsdam, Germany Abstract The impact of a climate change scenario on regional climate conditions and runoff characteristics has been investigated for the Mulde catchment, a meso-scale sub-basin of the Elbe in Germany. First, the semi-distributed, conceptual model HBV-D has been successfully applied to simulate discharge for present climate conditions. Further, the expanded downscaling method (EDS) was calibrated and applied to observed global circulation fields in order to produce local climate input data for HBV-D. Finally, the coupled atmosphere-ocean model ECHAM4/OPYC3, driven by a climate change scenario, provided simulated global circulation patterns for application with EDS. The regionalised scenario conditions then served as input to HBV-D in order to investigate the impact of global climate change on regional hydrology. The results indicate that an obvious increase in temperature is accompanied by a clear tendency to reduced precipitation over the investigated area for the next 100 years. These conditions lead to a decrease in simulated mean discharges of the Mulde. The study is considered to be a contribution for regional impact studies on global climate change. At the same time, it demonstrates existing shortcomings and limitations of current climate impact research. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Climate change; Global circulation models; Downscaling; Regional hydrology 1. Introduction There is no doubt that the increase in mean global surface temperature by 0.6 ^ 0.2 8C over the 20th century (IPCC, 2001) is not only a result of climate variability but of enhanced emission of greenhouse gases due to human activities. The 1990’s are considered to be the warmest decade of the last millennium, and a further and obvious increase in mean global air temperature is projected for the end of this century. An increase in surface temperature leads to higher evaporation rates and enables the atmos- phere to transport higher amounts of water vapour. Therefore, it is assumed that the global hydrological cycle will be accelerated. According to the Inter- governmental Panel on Climate Change (IPCC, 2001) an increase in precipitation is likely to affect large continental areas in the tropics and at higher latitudes. While a corresponding amplification in rainfall intensities is projected, precipitation variability may increase in other regions of the world. In contrast to the assessment of global or large- scale variations of the climatic driving forces for global hydrology the impact of climate change on the processes at the hydrological meso-scale is still unknown for most regions of the world; so far only a few studies exist (Menzel et al., 2002). This is especially true for hydrological extremes, such as floods and droughts. A main reason is the lack of spatial detail in global circulation models (GCMs) which makes it difficult to reflect the relatively 0022-1694/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S0022-1694(02)00139-7 Journal of Hydrology 267 (2002) 53–64 www.elsevier.com/locate/jhydrol * Corresponding author. Tel.: þ49-331-288-2673; fax: þ 49-331- 288-2695. E-mail address: menzel@pik-potsdam.de (L. Menzel).