CLIMATE CHANGE AND FUTURE HYDROCLIMATE FOR THE UPPER CROOKED RIVER, OREGON

Abstract

Upper Crooked River drains a semiarid elevated lava plain supporting a mixed vegetation cover of juniper, sagebrush, and grass. The majority of basin farm income is derived from livestock grazing on non-irrigated public and private land. Average annual water balance surplus is a modest 75 mm. A watershed model run for 108 consecutive months defines present-day hydroclimate as a basis for assessing changes related to global warming. Future watershed surplus is modeled assuming current land-use and grazing practices using monthly temperature and precipitation changes derived from a limited area model nested in a global circulation model. In the simulated warmer and wetter climate, peak surplus occurs three months earlier in January as an increased proportion of precipitation occurs as rain rather than snow. Severe decreases in water availability to plants accompany elevated evapotranspiration in all months. The sensitivity of the watershed to evapotranspiration is attributable to the cool season concentration of rainfall and evapotranspiration increases that magnify moisture deficits and drought in the summer. Compared to present-day climate, modeled future hydroclimate indicates severely limited watershed moisture supplies requiring flexible resource management plans. [Key words: hydroclimate, watershed model, climate change, Crooked River Basin.]