Ecosystem processes at the watershed scale: Sensitivity to potential climate change

A distributed data and simulation system for forested watersheds was used to investigate the potential changes in watershed hydrological and ecological processes under hypothesized climate change scenarios. RHESSys (Regional HydroEcological Simulation System) incorporates a spatial representation of nested catchment and lake systems in a GIS, along with a set of process submodels to compute local flux and storage of energy, water, carbon, and nutrients. A hierarchy of potential climate change shifts in weather, forest canopy physiological processes, and forest cover were used to operate RHESSys for comparison with control simulations for present-day conditions. Use of projected temperature and precipitation changes alone led to qualitatively different forecasts of watershed climate change impact when compared to simulations that also incorporated adjustment of canopy physiology to elevated concentrations of atmospheric CO₂. In addition, ecosystem processes may be more resilient to climate change due to the existence of a series of offsetting effects. Annual net effects on specific processes such as watershed outflow and forest productivity may qualitatively vary from year to year rather than showing consistent increases or decreases relative to current conditions. The model results illustrate the significance of incorporating a reasonable description of terrestrial ecosystem processes within the contributing watershed when assessing the impact of climate change.