Modeling Renewable Water Resources under Climate Change

Abstract:

The impacts of climate change on renewable water resources are usually assessed using hydrological models driven by downscaled climate outputs from global climate models. Most hydrological models do not have explicit parameterization of vegetation and thus are unable to assess the effects of elevated atmospheric CO₂ on stomatal conductance and water loss of leaf. The response of vegetation to elevated atmospheric CO₂ would reduce evaporation and affect runoff and renewable water resources. To date, the impacts of elevated CO₂ on vegetation transpiration were not well addressed in assessment of water resources under climate change. In this study, the distributed biosphere-hydrological (DBH) model, which incorporates a simple biosphere model into a distributed hydrological scheme, was used to assess the impacts of elevated CO₂ on vegetation transpiration and consequent runoff. The DBH model was driven by five General Circulation Models (GCMs) under four Representative Concentration Pathways (RCPs). For each climate scenario, two model experiments were conducted. The atmospheric CO₂ concentration in one experiment was assumed to remain at the level of 2000 and increased as described by the RCPs in the other experiment. The results showed that the elevated CO₂ would result in decrease in evapotranspiration, increase in runoff, and have considerable impacts on water resources. However, CO₂ induced runoff change is generally small in dry areas likely because vegetation is usually sparse in the arid area.