ECOSYSTEM PROCESSES AT THE WATERSHED SCALE - SENSITIVITY TO POTENTIALCLIMATE-CHANGE

A distributed data and simulation system for forested watersheds was u sed to investigate the potential changes in watershed hydrological and ecological processes under hypothesized climate change scenarios. RHE SSys (Regional HydroEcological Simulation System) incorporates a spati al 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 a nd precipitation changes alone led to qualitatively different forecast s of watershed climate change impact when compared to simulations that also incorporated adjustment of canopy physiology to elevated concent rations of atmospheric CO,. In addition, ecosystem processes may be mo re resilient to climate change due to the existence of a series of off setting effects. Annual net effects on specific processes such as wate rshed outflow and forest productivity may qualitatively vary from year to year rather than showing consistent increases or decreases relativ e to current conditions. The model results illustrate the significance of incorporating a reasonable description of terrestrial ecosystem pr ocesses within the contributing watershed when assessing the impact of climate change.