How reservoir regulation modifies the regional terrestrial-atmospheric water cycle: Incorporation of a reservoir network module into a fully-coupled hydrological-atmospheric model

The regional terrestrial-atmospheric water cycle is strongly altered by human activities. Among them, reservoir regulation is a way to spatially and temporally allocate the water resources in a basin for the purpose of, for example, flood control, agriculture development, ecosystem maintenance. However, it is still not well understood how the reservoir regulation modifies the regional terrestrial-atmospheric water cycle. To address this question, this study employs a fully-coupled regional Earth system modelling system WRF-HMS, which has a closed description of the water cycle in a ground-soil-vegetation-atmosphere continuum. A process-based reservoir regulation module is for the first time now implemented into WRF-HMS, which allows to represent reservoir regulation in one seamless atmosphere-hydrology modeling system. In addition, an online budget analysis of atmospheric moisture is implemented into WRF-HMS, so that the impact of reservoir regulation on the atmospheric branch of the water cycle is quantitatively analyzed. Our study focuses on the basin of the largest fresh water lake in China, the Poyang Lake basin. Four simulations with a horizontal resolution of 10 km are conducted for the investigation period of 1979 to 1986: the standalone HMS with/without the reservoir regulation module and the fully-coupled WRF-HMS with/without the reservoir regulation module. For the standalone simulations, the basin-averaged, multi-year mean results show that incorporating reservoir regulation leads to an increased evapotranspiration, a wetter soil, and a higher groundwater level. In addition, the interactions among river water, unsaturated zone, and groundwater are enhanced as well. Overall, the reservoir-enabled HMS model improves the streamflow simulation over the Poyang Lake basin on daily and monthly scales than the reservoir-disabled HMS model. For the fully coupled simulations, our preliminary results show that incorporating reservoir regulation also modifies the regional atmospheric branch of the water cycle, for example, moistening planetary boundary layer due to the enhanced evapotranspiration. Details about the results of the fully-coupled simulations will be presented in the conference.