The uncertainties of climate model results, however, remain very large in terms of hydrological forecasting, particularly at the regional scale. This limitation is particularly critical for water management practices in the future because water resource impacts occur at the local scale, not at regional or larger scales. The results of catchment-scale simulations with conventional hydrological models driven by GCM data therefore are highly variable. Another consequence of increasing temperatures is a change in the distribution of water in the landscape. According to current and projected distributions of rainfall, there may be an increase in summer drought.
Observed precipitation shows a decrease in summer and an increase in winter and spring.
Additional consumption of water for irrigation may create additional depletion of water reservoirs and groundwater. An increase in large-scale precipitation might lead to increased flood risks on large river basins in western Europe in winter. The increased temperatures expected in summer could lead to higher local precipitation extremes and associated flood risks in small catchment areas. Under laboratory and greenhouse conditions, plants seem to use less water for constant yield or exhibit higher productivity. In the field, however, predictions of WUE at the catchment or even ecosystem level are not yet feasible.