CLIMATE-CHANGE IMPACTS ON THE HYDROLOGIC RESOURCES OF SOUTH-AMERICA -AN ANNUAL, CONTINENTAL-SCALE ASSESSMENT

Two empirical annual runoff models which represent point estimates of river basin discharge were used for assessing the potential impact of climate change on runoff over South America. The first model is an ann ual regression relationship which relates temperature and precipitatio n to basin discharge. The second relationship is based on observed cli matological variables and relates annual precipitation and potential e vapotranspiration to runoff. A Geographic Information System (GIS) was used to implement these annual models in order to assess runoff on a 0.5 degrees x 0.5 degrees grid over South America using mean annual te mperature, precipitation, and computed potential evapotranspiration im ages. Annual changes in precipitation (percent change) and temperature (absolute change) were gathered from 4 Global Circulation Models (GCM s) and were used to derive new runoff estimates. Generally, these clim ate change scenarios consistently showed increases in runoff over the northwest and southern regions of South America, while the central and northeast regions were a mixture of increases and decreases depending on the GCM scenario. Comparisons with detailed, basin level models wi th shorter time-steps are necessary to validate the use of these annua l approaches for continental scale assessment.