Climate change and future hydroclimate for the Upper Crooked River, Oregon

Upper Crooked River drains a semiarid elevated lava plain supporting a mixe d vegetation cover of juniper, sagebrush, and grass. The majority of basin farm income is derived from livestock grazing on non-irrigated public and p rivate land. Average annual water balance surplus is a modest 75 mm. A wate rshed model run for 108 consecutive months defines present-clay hydroclimat e as a basis for assessing changes related to global warming. Future waters hed surplus is modeled assuming current land-use and grazing practices usin g monthly temperature and precipitation changes derived from a limited area model nested in a global circulation model. In the simulated warmer and we tter climate, peak surplus occurs three months earlier in January as an inc reased proportion of precipitation occurs as rain rather than snow Severe d ecreases in water availability to plants accompany elevated evapotranspirat ion in all months. The sensitivity of the watershed to evapotranspiration i s attributable to the cool season concentration of rainfall and evapotransp iration increases that magnify moisture deficits and drought in the summer. Compared to present-day climate, modeled future hydroclimate indicates sev erely limited watershed moisture supplies requiring flexible resource manag ement plans.