Uncertainty Analysis of the Impact of Climate Change on the Availability of Surface Water Resources

Currently, the elements of the water cycle, such as temperature, precipitation, evapotranspiration and streamflow, are the major factors incorporated in studies on the climate change impacts on water resources. Other factors that are directly used in the design of water engineering and the planning of water resources development and management, such as water availability, water supplies and demands, are rarely considered, although they are also sensitive to climate change. To this end, the application of climate change results to the design of water engineering and the planning of water resources development and management is facing the challenge of uncertainty. Taking the upstream watershed in the Hanjiang basin as an example, two results as to the impact of climate change on streamflow were compared and analyzed in detail. The two schemes that utilized different GCMs and hydrologic models, the statistic downscaling methods and the weather generator were applied to couple the GCMs and the hydrologic models. There existed obvious differences in the two results. It was revealed that one of the sources of uncertainty in the prediction of streamflow is that the impact of climate change on the underlying conditions in watersheds has not yet been considered in hydrologic modeling. Based on the predicted streamflow in the upstream watershed in the Hanjiang basin, the availability of surface water resources is evaluated by means of the losing deduction. It was also found that there were pronounced uncertainties associated with the evaluation of the availability of surface water resources because the impact of climate change on the key variables that should be calculated in the losing deduction method, such as ecological water demands and high flow during flooding season, were not considered. The total uncertainties caused by the coupling of the impacts of climate change on streamflow and on the ecological water demands as well as the high flow during flooding season, significantly reduced the reliability of the evaluation of the availability of surface water resources. In order to apply the results on climate change to the design of water engineering and the planning of water resources development and management, the modeling and predicting reliability of related elements of climate, the response of the factors affecting runoff generation and related planning components with regard to climate change should be comprehensively evaluated.