Using GCM scenarios for regional modelling

The most widely used climate change projections are provided by the Intergovernmental Panel on Climate Change (IPCC, 2001). These projections are based on outputs of general circulation models (GCMs) and are used in many studies that assess impacts of climate change on hydrology. A major weakness of using GCM outputs for regional impact studies is that the spatial and temporal resolution of current climate model outputs is too coarse to be used directly in (regional) hydro-logical models.

To prepare the coarse GCM data for regional studies, downscaling techniques can be used. Four methods have been explored within the ADAPT project. The results for the baseline period (1961-1990) were compared in graphs and tables using statistical test parameters. It appears that each method generates substantially different results. The commonly employed downscaling technique that correct future projections based on annual and monthly mean averages perform relatively badly compared to methods that differentiate corrections across all cells. The best downscaling method (method 4, Chapter 2) corrects the GCM outputs using the variance of the measured data.

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