Regional precipitation and temperature scenarios for climate change

To investigate the consequences of climate change on the water budget in sm all catchments, it is necessary to know the change of local precipitation a nd temperature. General Circulation Models (GCM) cannot provide regional cl imate parameters yet, because of their coarse resolution and imprecise mode lling of precipitation. Therefore downscaling of precipitation and temperat ure has to be carried out from the GCM grids to a small scale of a Few squa re kilometres. Daily rainfall and temperature are modelled as processes con ditioned on atmospheric circulation. Rainfall is linked to the circulation patterns (CPs) using conditional probabilities and conditional rainfall amo unt distribution. Both temperature and precipitation are downscaled to seve ral locations simultaneously taking into account the CP dependent spatial c orrelation. Temperature is modelled using a simple autoregressive approach, conditioned on atmospheric circulation and local areal precipitation. The model uses the classification scheme of the German Weather Service and a fu zzy rule-based classification. It was applied in the Aller catchment for va lidation using observed rainfall and temperature, and observed classified g eopotential pressure heights. GCM scenarios of the ECHAM model were used to make climate change predictions (using classified GCM geopotential heights ); simulated values agree fairly well with historical data. Results for dif ferent GCM scenarios are shown.