DEVELOPMENT OF A COUPLED WATERSHED HYDROLOGY AND STREAM TEMPERATURE MODEL AND ITS USE IN EVALUATION OF FUTURE CLIMATE SCENARIOS IN THE APALACHICOLA-CHATTAHOOCHEE-FLINT RIVER, SOUTHEASTERN UNITED STATE

Water temperature is a fundamentally important parameter in the natural development of freshwater riverine ecosystems. The interactions of flora and fauna with chemical constituents, dissolved oxygen and other water quality factors all are dependent on the temperature of the water in the stream. Development of computer models and methods that simulate stream temperature for watersheds at stream segment resolution can provide useful information to ecologists and resource managers. Modeling challenges include sufficiently characterizing the real world to support the level of detail in the algorithms, while simulating at a fine enough resolution to support segment-scale applications. This is particularly true when evaluating the vulnerability of stream water temperature with respect to potential climate change because of uncertainty associated with trying to characterize the future.

A coupled model has been developed which simulates stream flow rates and in-stream water temperatures on a daily time step. The approach uses the Precipitation-Runoff Modeling System (PRMS) watershed hydrology model to simulate the hydrologic response of a watershed to land cover and climatic conditions, and the Stream Network Temperature Model (SNTemp) to simulate the energy balance and mean daily water temperature for each stream segment in the watershed. These two models are run sequentially; with the output from the PRMS model used as input to the SNTemp model.

The Apalachicola-Chattahoochee-Flint River Basin (ACFB) in the southeastern United States was selected as the initial application site because of increasing urbanization, severe droughts in recent years, higher consumptive demands for the water, and identification of several ecologically sensitive stream segments. The ACFB covers an area of 50,000 square kilometers. The coupled model was calibrated and evaluated with historical stream temperature data from 13 locations within the basin. Future projections were made using daily time step climate forcings from several of the Intergovernmental Panel on Climate Change carbon emission scenarios. Overviews of development, calibration, and results are presented.