POTENTIAL WATER-BALANCE RESPONSE TO CLIMATIC WARMING - THE CASE OF A COASTAL WETLAND ECOSYSTEM OF THE JAMES BAY LOWLAND

The present study investigates the potential impacts of climate warming on the water balance and vegetation patterns in a coastal wetland ecosystem on James Bay, Canada. The study illustrates some of the linkages within this system and how they might respond to a change in mean summer temperature. These linkages are outlined in a simple conceptual model with hydrology, salinity, topography, and vegetation distribution components. The model includes two feedbacks: a vegetation/evaporation feedback, and a hydrologic, runoff/storage feedback. A mathematical model is developed to examine changes in evaporation and water balance under a range of temperature change scenarios. Although the model is relatively insensitive to the internal feedbacks, model runs for temperature-change scenarios of +2 to +8 degrees C above present summertime normal showed evaporation increased by 18 to 64%, respectively, which resulted in decreases in wetland water table of 40 to 129% below the normal summer drawdown. These changes in basin storage significantly affect the distribution of woody species in the wetland. The basin area inhabited by woody species increased from the present 25% to 32% for a +2 degrees C temperature change and to 51% for a +8 degrees C change. Increased stomatal resistance of the wetland vegetation, which might result from increased CO, concentrations, partially offsets the evaporation enhancement from warmer summer temperatures.