Simulations of the ENSO hydroclimate signals in the Pacific Northwest Columbia River basin

Natural fluctuations in the atmosphere-ocean system related to the El Nino- Southern Oscillation (ENSO) induce climate variability over many parts of t he world that is potentially predictable with lead times from seasons to de cades. This study examines the potential of using a model nesting approach to provide seasonal climate and streamflow forecasts suitable for water res ources management. Two ensembles of perpetual January simulations were perf ormed with a regional climate model driven by a general circulation model ( GCM), using observed climatological sea surface temperature (SST) and the m ean SST of the warm ENSO years between 1950 and 1994. The climate simulatio ns were then used to drive a macroscale hydrology model to simulate streamf low. The differences between the two ensembles of simulations are defined a s the warm ENSO signals. The simulated hydroclimate signals were compared with observations. The ana lyses focus on the Columbia River basin in the Pacific Northwest. Results s how that the global and regional models simulated a warming over the Pacifi c Northwest that is quite close to the observations. The models also correc tly captured the strong wet signal over California and the weak dry signal over the Pacific Northwest during warm ENSO years. The regional climate mod el consistently performed better than the GCM in simulating the spatial dis tribution of regional climate and climate signals. When the climate simulat ions were used to drive a macroscale hydrology model at the Columbia River basin, the simulated streamflow signal resembles that derived from hydrolog ical simulations driven by observed climate. The streamflow simulations wer e considerably improved when a simple bias correction scheme was applied to the climate simulations. The coupled regional climate and macroscale hydro logic simulations demonstrate the prospect for generating and utilizing sea sonal climate forecasts for managing reservoirs.