Projecting climate change impact on water-carbon cycling in the conterminous United States

The ongoing greenhouse gases (GHGs) emission and associated atmospheric processes have extensive impacts on regional climate and water-carbon cycling at broad scales. We projected potential climate change and its influences on ecohydrology using datasets derived from multiple global and regional climate models over the conterminous U.S. (CONUS). We find that future warming climate may alter the water partitioning pattern profoundly by enhancing evapotranspiration (ET) and depressing runoff. Overall, the role of rising temperature is likely to outweigh that of precipitation in controlling annual runoff in the later part of the 21st century, leading to an overall decrease of 8 30 mm yr-1 (3% 11%) in runoff. Due to the tight linkage between water and carbon cycles, such decrease in runoff and increase in ET may cause significant divergence in future ecosystem services of water supply and carbon sequestration. Our evaluation in the 170 National Forests and Grasslands across the CONUS suggests an average decrease by 18 31 mm yr-1 (4% 7%) in water yield and an increase by 76 229 g C m-2 yr-1 (8% 24%) in ecosystem productivity by 2100. Moreover, atmospheric aerosols may interact with GHGs and affect terrestrial hydrological cycle and ecosystem functions. We investigated the individual and combined impacts of climate change and air pollution on water-carbon cycling over the CONUS by connecting a regional climate model with sophisticated chemistry-aerosol modules and an ecohydrological model. The results indicate that regional air pollution may largely suppress water and carbon fluxes, and particularly aggravate regional climate change impacts on water shortage.