Impacts of the climate change on runoff and diffuse phosphorus load to Lake Balaton (Hungary).

The paper outlines a multi-component assessment of the impacts of the climate change on runoff and total phosphorus loads to the large shallow Lake Balaton in Hungary. Present hydrological cycle of the lake catchment has been examined using the rainfall-runoff model WetSpa. Particular phosphorus concentration in runoff was estimated on the basis of the simulated streamflow using an empirical power equation. Dissolved phosphorus concentrations were determined as a function of landuse and soil type of the corresponding sub-catchment. The model was calibrated and validated against daily observations manually at monitoring sites of sixteen inflowing streams around the lake. Runoff stemming from shoreline urban developments was calculated by the urban runoff simulation model SWMM. Phosphorus concentrations in urban runoff were calculated by an empirical relationship derived from field measurements. The model was henceforward run for climate change scenario analysis. Present weather data were modified by the climate change scenarios imported from the results of the CLIME project. The results indicate that the impact of the climate change on runoff and phosphorus load appears in the change of the distribution within a time period rather than in the total volume. However, due to the high uncertainties in climate models, the presented calculations are possible assumptions rather than established statements.