A comparative analysis of hydrologic responses of tropical deciduous and temperate deciduous watershed ecosystems to climatic change

Long-term monitoring of ecological and hydrological processes is critical to understanding ecosystem function and responses to anthropogenic and natural disturbances. Much of the world's knowledge of ecosystem responses to disturbance comes from long-term studies on gaged watersheds. However, there are relatively few long-term sites due to the large cost and commitment required to establish and maintain them. Knowledge gained from these sites is also important for predicting responses to future disturbances, such as climatic change, and these sites should be the focal point for the development and validation of predictive models. In this study, we apply a hydrologic model (PROSPER) using climate, vegetation, and soil parameters from watersheds in the mesic Southeastern United States and in the dry tropical forests of Western Mexico to assess the overall effects of climatic change (increased temperature and [CO2]) on watershed hydrology. We found that evapotranspiration (ET) increased substantially in both ecosystem types, with increases ranging from 24 to 42 percent. These increases were directly attributable to changes in leaf energy balance and evaporative demand. Streamflow decreased more substantially, with virtually no streamflow under the greatest temperature increase scenario (+20 percent) at the site in Western Mexico. Decreased stomatal conductance was not sufficient to offset the effects of increased temperature.