Many water authorities are concerned with the impacts of and adaptation to climate change. The basis for climate change impact analysis at the river basin scale is formed of climate change projections at the global scale using General Circulation Models (GCM). These models simulate the future climate (up to the year 2100) according to different development scenarios quantified in terms of emission scenarios for CO2 and other greenhouse gases. In reports from the Intergovernmental Panel on Climate Change, results from GCMs are reported, each considering several emission scenarios. The GCMs model the atmosphere on a rather coarse horizontal scale (typically of the order of 200-300 km). For climate change studies, therefore, it is necessary to downscale the climate change projections.
Dynamic downscaling is based on Regional Climate Models (RCM), which use GCMs as boundary conditions to simulate the state of the atmosphere in a region with a smaller grid resolution than that used in the GCM. RCM models are usually defined on a grid size of 10-50 km and are able to better represent topography and land use heterogeneities than GCM models. Statistical downscaling procedures may be required for different types of applications, ranging from simple mean correction (delta change) procedures to more complex stochastic weather generator procedures, which provide more reliable downscaling of extreme events. In order to facilitate the analysis of climate change impact and adaptation, a DSS should be able to use (or simply include) the climate change projection data produced by the GCM simulations.

(GWP 2013b)