Case study on impact of atmospheric circulation changes on river basin hydrology: uncertainty aspects

Abstract Significance of predictions concerning the climate change impact on basin hydrology in case of doubled CO 2 concentration in the atmosphere (2×CO 2 -case) is investigated within the context of a case study for the Mesohora basin in Greece. Circulation patterns (CPs) characterizing the weather in the region are defined based on wind direction and on barometric conditions and the modification of the large-scale atmospheric variables (geopotential height, occurrence probability and duration of CPs) in 2×CO 2 -case is estimated. The effect of the atmospheric-variables modification on temperature and precipitation on basin scale is predicted by means of a semiempirical, purely circulation-based downscaling model. Temperature modification in 2×CO 2 -case has been found to be significant for eight months of the year with a maximal increase of mean monthly temperature approximately 2°C. For precipitation, significant change has been predicted for one of the precipitation stations considered. Owing to the fact that this precipitation change does not influence mean precipitation of the basin, climate change impact on basin runoff has been investigated only for temperature effects. For this purpose a hydrological model has been used. It has been found that the error of hydrologic model is significantly larger than climate change impact so that modifications of the river basin hydrology for the 2×CO 2 -case can be hardly predicted.