OBSERVED SACRAMENTO BASIN STREAMFLOW RESPONSE TO PRECIPITATION AND TEMPERATURE-CHANGES AND ITS RELEVANCE TO CLIMATE IMPACT STUDIES

Observational studies of Sacramento Basin annual mean streamflow respo nse to precipitation and temperature indicate that streamflow amounts in the basin are strongly sensitive to precipitation, but virtually in sensitive to mean seasonal temperature. This result is in accord with studies of the climate mean sensitivity of streamflow amount to change s in climatological mean precipitation and temperature as simulated by conceptual hydrological models of the basin. Simpler regression model s of the Sacramento Basin show a strong dependence of streamflow amoun t on temperature, which is not evident in the observation-based annual mean streamflow sensitivity. The interannual variability in Sacrament o Basin streamflow response to precipitation exhibits substantial nonl inearity in that the partitioning of precipitation to runoff strongly depends on the precipitation volume. During very wet years in the basi n, streamflow response to precipitation exhibits a proportionally grea ter change (increase) than during normal or dry years. For most dry ye ars in the basin the streamflow response to precipitation is fairly li near. However, on the tails of droughts the streamflow response to pre cipitation is diminished relative to other dry years. This implies tha t a shift to a much drier or more drought-prone climate would result i n a more substantial reduction in streamflow amounts than might at pre sent be expected from observations of streamflow responses in isolated dry years. This conclusion assumes no changes in the features control ling water retention in the basin, which is an important issue to be a ddressed in basin climate change studies.