Development and Testing of Methods to Assess The Impact of Climate Change on Flood And Drought Hazards at The European Scale


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During the last 100 years global climate has warmed by an average of 0.6ºC, owing in part to human induced greenhouse gas emissions. Based on different scenarios of future greenhouse gas emissions, projections of climate models indicate another 1.4 to 5.8 ºC of warming over the next century (IPCC, 2001a). The projected change in climate will significantly impact the hydrological cycle. A warmer climate will increase evaporation, the intensity of water cycling, and result in greater amounts of moisture in the air. It is expected that the magnitude and frequency of extreme weather events will increase, and that hydrological extremes such as floods and droughts will likely be more frequent and severe.

The Joint Research Centre aims to develop knowledge and tools in support of the EU Climate Change Strategy that was recently put forward in the Commission’s Communication “Winning the Battle Against Global Climate Change” (COM(2005) 35). In view of this, an important research topic of the Land Management Unit of the IES is to assess the impact of climate change on the occurrence of hydrological extremes such as floods and droughts. This will be accomplished by developing an integrated modelling framework that combines regional climate predictions for Europe with the LISFLOOD model. LISFLOOD is a distributed, partially physicallybased rainfall-runoff model that has been devised to simulate the hydrological behaviour in large European catchments (De Roo et al., 2000), with emphasis on predicting floods and droughts. Owing to its general nature, LISFLOOD is optimally suited for simulating the different hydrological regimes across Europe.

Projections of future climate change are typically obtained from coupled Atmosphere- Ocean General Circulation Models (AOGCM). Because they require time steps of minutes but are used to predict climate change on time scales of months to centuries, their horizontal resolution is typically at least 100 km. As a result, their treatment of physical processes is approximate. Due to the coarse spatial resolution AOGCMs also fail to explicitly capture fine-scale climatic structures needed for climate change impact studies and policy planning at the regional or sub-regional scale (e.g., catchment or basin scale). To resolve this problem, regionalization or downscaling 8 methods can be used, which enhance regional detail and provide climatic information at regional scales.

The downscaled predicted climate for current conditions and for different scenarios of greenhouse gas emissions by the end of the 21st century will be used as input to LISFLOOD, after taking due account of any systematic bias in the regional climate data. Runoff statistics for the two periods will provide a means to estimate changes in the frequency and severity of hydrological extremes under different scenarios of future greenhouse gas emissions.

The aim of this document is to present the current status of the integrated modelling framework that is being developed to assess the impact of climate change on flood and drought hazards at the European scale. The document is organised as follows. Section 2 presents a general overview of existing downscaling methods, with details of the underlying principles to generate regional climate information. In Section 3 details about existing regional climate data sets for Europe are presented. Section 4 describes the integrated modelling framework that couples the regional climate model data with the hydrological model LISFLOOD. Some initial results of a pilot study in the Meuse catchment are presented in Section 5. Conclusions and an overview of current and further work are presented in Section 6.

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