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item SKILES, J.W. - NASA
item Hanson, Jonathan

Submitted to: Climatic Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: The effect of predicted climate change on the water supply of rangelands is a critical issue, because so much of our water comes directly from these areas. The only way to investigate the effect of climate chane on rangelands is through simulation modeling. The SPUR model was used to examine the consequences of changes in precipitaion, temperature, and CO2 induced plant-function characteristics on runoff from a small-basin. We concluded there would be little change or an actual decrease in surface runoff because because of increased CO2 and climate change. The reuslt was realized because of the plant response to decreased precipitaion. The results from this simulation study have repercussions for land-use planners and water resource managers. Changes in water budgets of rural basins will influence water harvest and consumption by urban localities, determine which and how much of what crops are grown in agricultural areas, and determine the amount and quality of water available for alternative use, e.g. recreation.

Technical Abstract: The atmospheric concentration of carbon dioxide is expected to double in the next century causing increased temperatures and decreasing precipitaion in some regions of the U.S. The increase in CO2 will also directly affect somatal conductance of plants. At the first-order watershed scale, changes in evaporative demand, transpiration, and runoff will also occur. Previous modeling studies of the effect of increased CO on the water budgets of watersheds have been single-factor exercises where a single parameter representing stomatal conductance was reduced and the results noted. After showing validation results of the hydrology module, we used a comprehensive ecosystem model to examine the consequences of changes in precipitaion, temperaturem and CO2-induced plant-function characteristics on a small-basin runoff. As a result of the complex interactions and of the coompensatory mechanisms simulated by the model, we econclude that for arid and semiarid watersheds of the western United States, there will be little change or an actual decrease in surface runoff because of increased CO2 and climate change. This is due to the decrease in precipitation imposed on the model simulations. Implementing stomatal closure in the model did not increase runoff from t he watersheds when temperatures and precipitation decreased.