Climate change impacts on the water balance - case studies in Hungarian watersheds

Climate change will alter various components of the water balance on global, regional, and local scales; these changes will be measurable mainly through alterations of the spatial distribution and temporal trends of temperature, precipitation, and evapotranspiration. We analyzed the water balance of two Hungarian watersheds (Zala and Bacsbokodi-Kigyos) based on a spatially distributed robust hydrological model that was calibrated using actual evapotranspiration values of CREMAP (Complementary-relationship-based Evapotranspiration Mapping Technique). During the model calibration period (2000-2008), evapotranspiration (ET) and runoff (or recharge, R) were 92% and 8% of the precipitation amount in the Zala watershed, while in the Bacsbokodi-Kigyos watershed it was 75% and 25%. A climate-runoff model was developed to evaluate the effects of climate change on the water balance. Long-term ET and R averages can be calculated applying a spatially distributed Budyko-model at a resolution of 1 km x 1 km. In the case of the surplus water affected areas where ET exceeds precipitation, ET and R can be calculated with another simple model that works on the analogy of pan evaporation. Using precipitation and temperature results of regional climate model simulations as input data, we calculated the projections of the main components of the water balance. Increasing temperatures in the 21st century are projected to cause a slight increase in evapotranspiration relative to the reference period 1981-2010; this may cause a substantial reduction of long-term runoff. The mean decrease can exceed 53% for the Zala and 38% for the Bacsbokodi-Kigyos watersheds. The decreasing runoff/recharge could limit manageable or extractable groundwater resources, alter agricultural activities, and cause a water deficit in Balaton Lake.