Abstract: Down-scaled climate projections for eight demonstration catchments under different SRES scenarios
Detailed projections of future climate change are required to evaluate its impacts on functioning of aquatic ecosystems and to develop strategies for ecosystem management at the catchment scale. The most appropriate approach is that developed by the FP6 ENSEMBLES project which generated an ensemble prediction system for climate change based on the principal state-of-the-art, high resolution, global and regional Earth System Models. These allow an objective probabilistic estimate of uncertainty in future climate at the seasonal to decadal and longer timescales. In REFRESH we have used ENSEMBLES output to generate climate scenarios for eight demonstration catchments. These will feed into subsequent modelling and storyline generation in Task 3.1, WP5, WP6 and WP7. This report introduces the use of scenarios in REFRESH and summarises the methods involved. Monthly averages of surface air temperatures, daily precipitation rates and daily evaporation rates for each of the demonstration catchments are available on the REFRESH file store together with the validation results for air temperature and precipitation. This is an internal deliverable making available the output from the climate scenarios to the modellers from each of the demonstration catchments.
Plans have been revised to use the outputs from three GCM-RCM combinations to cover the mean and extreme warm-dry and cold-wet projections from the ENSEMBLES project and these will be used where resources allow. The precipitation and temperature projections of ECHAM5-KNMI have already been, or are planned to be, bias corrected for each demonstration catchment. The climate projections from the other two climate models will be bias corrected as they are needed. A single RACMO-ECHAM5 combination of models was chosen initially because it is the combination that provides data that is closest to ENSEMBLES group of models average. Where other climate scenarios are to be used, we suggest using two other models - HadRM3-HadCM3 and SMHIRCA-BCM - as the models with especially high and low climate sensitivities respectively. This combination of three climate models outputs will allow us to sample the uncertainty due to the choice of climate models and evaluate impacts for average, strong, and weak climate change signals.
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