WATERSHED HETEROGENEITY AND THE RESPONSE TO 2 × CO2 CLIMATE: A CASE STUDY FROM THE UPPER DESCHUTES BASIN, OREGON

Abstract

A fully allocated surface water supply in the Upper Deschutes Basin, Oregon, intensifies concern for the watershed's response to climate change. Such concern provides the impetus for this case study of the basin under a potential doubling of atmospheric trace gas concentrations (2 × CO₂). Modeling the watershed as four sectors incorporates climate and landscape heterogeneity and defines a control climate that closely simulates adjusted gaged runoff. Monthly temperature and precipitation from a limited area model nested in a global circulation model define changes for modeling the watershed 2 × CO₂ climate. Precipitation increases are greatest in the Wickiup sector and least in the Little Deschutes sector for a 2 × CO₂ climate, but snow-water equivalent decreases substantially in all sectors. Summer water deficits are extended and magnified in all sectors and increase by 175% in the Wickiup sector. Water surplus increases range from 34% for Wickiup to 5% for Benham Falls. Average monthly runoff for the Upper Deschutes Basin increases by 7 mm or 24% in the 2 × CO₂ climate, but the greatest monthly runoff differences are for the Crescent Lake sector, where February and March runoff increase by 68% and May runoff decreases by 10%. The earlier occurrence of maximum and minimum 2 × CO₂ climate runoff of one to five months significantly alters the Upper Deschutes Basin runoff regime. [Key words: mesoscale hydroclimate model, climate change, Deschutes River Basin.]