The Columbia Basin Climate Change Scenarios Project (CBCCSP) was conceived as a comprehensive hydrologic database to support climate change planning, impacts assessment, and adaptation in the Pacific Northwest (PNW) by a diverse user community with varying technical capacity over a wide range of spatial scales. The study has constructed a state-of-the-art, end-to-end data processing sequence from "raw" climate model output to a suite of hydrologic modelling products that are served to the user community from a web-accessible database. A calibrated 1/16 degree latitude-longitude resolution implementation of the VIC hydrologic model over the Columbia River basin was used to produce historical simulations and 77 future hydrologic projections associated with three different statistical downscaling methods and three future time periods (2020s, 2040s, and 2080s). Key products from the study include summary data for about 300 river locations in the PNW and monthly Geographic Information System products for 21 hydrologic variables over the entire study domain. Results from the study show profound changes in spring snowpack and fundamental shifts from snow and mixed-rain-and-snow to rain-dominant behaviour across most of the domain. Associated shifts in streamflow timing from spring and summer to winter are also evident in basins with significant snow accumulation in winter (for the current climate). Potential evapotranspiration increases over most of the PNW in summer because of rising temperatures; however, actual evapotranspiration is reduced in all but a few areas of the domain because evapotranspiration is mostly water limited in summer, and summer precipitation decreases in the simulations. Simulated widespread increases in soil moisture recharge in fall and winter in areas with significant snow accumulation in winter (for the current climate) support hypotheses of increased landslide risk and sediment transport in winter in the future. Simulations of floods and extreme low flows increase in intensity for most of the river sites included in the study. The largest increases in flooding are in mixed-rain-and-snow basins whose current mid-winter temperatures are within a few degrees of freezing. The CBCCSP database has been a valuable public resource that has dramatically reduced costs in a number of high-visibility studies in the PNW and western United States focused on technical coordination and planning. « neige ou pluie et neige mêlées » vers « principalement pluie » dans presque tout le domaine. Des déplacements correspondants des caractéristiques d'écoulement fluvial du printemps et de l'été vers l'hiver sont également évi-dents dans les bassins où l'accumulation de neige est importante en hiver (sous le climat actuel). L'évapotranspira-tion potentielle augmente dans la majeure partie de la région du Pacifique et du Nord-Ouest en été à cause des températures plus élevées; cependant, l'évaporation réelle est réduite dans presque tous les secteurs du domaine parce que l'évapotranspiration est principaleme...

Boreal species sensitive to the timing and duration of snow cover are particularly vulnerable to global climate change. Recent work has shown a link between wolverine (Gulo gulo) habitat and persistent spring snow cover through 15 May, the approximate end of the wolverine's reproductive denning period. We modeled the distribution of snow cover within the Columbia, Upper Missouri, and Upper Colorado River Basins using a downscaled ensemble climate model. The ensemble model was based on the arithmetic mean of 10 global climate models (GCMs) that best fit historical climate trends and patterns within these three basins. Snow cover was estimated from resulting downscaled temperature and precipitation patterns using a hydrologic model. We bracketed our ensemble model predictions by analyzing warm (miroc 3.2) and cool (pcm1) downscaled GCMs. Because Moderate‐Resolution Imaging Spectroradiometer (MODIS)‐based snow cover relationships were analyzed at much finer grain than downscaled GCM output, we conducted a second analysis based on MODIS‐based snow cover that persisted through 29 May, simulating the onset of spring two weeks earlier in the year. Based on the downscaled ensemble model, 67% of predicted spring snow cover will persist within the study area through 2030–2059, and 37% through 2070–2099. Estimated snow cover for the ensemble model during the period 2070–2099 was similar to persistent MODIS snow cover through 29 May. Losses in snow cover were greatest at the southern periphery of the study area (Oregon, Utah, and New Mexico, USA) and least in British Columbia, Canada. Contiguous areas of spring snow cover become smaller and more isolated over time, but large (>1000 km2) contiguous areas of wolverine habitat are predicted to persist within the study area throughout the 21st century for all projections. Areas that retain snow cover throughout the 21st century are British Columbia, north‐central Washington, northwestern Montana, and the Greater Yellowstone Area. By the late 21st century, dispersal modeling indicates that habitat isolation at or above levels associated with genetic isolation of wolverine populations becomes widespread. Overall, we expect wolverine habitat to persist throughout the species range at least for the first half of the 21st century, but populations will likely become smaller and more isolated.

[1] Measurements of aerosol and cloud properties in the Eastern Pacific Ocean were taken during an airborne experiment on the University of Wyoming's King Air during April 2004 as part of the Cloud Indirect Forcing Experiment (CIFEX). We observed a wide variety of aerosols, including those of long-range transport from Asia, clean marine boundary layer, and North American emissions. These aerosols, classified by their size distribution and history, were found in stratified layers between 500 to 7500 m above sea level and thicknesses from 100 to 3000 m. A comparison of the aerosol size distributions to measurements of cloud condensation nuclei (CCN) provides insight to the CCN activity of the different aerosol types. The overall ratio of measured to predicted CCN concentration (N CCN ) is 0.56 ± 0.41 with a relationship of N CCN,measured = N CCN,predicted 0.846±0.002 for 23 research flights and 1884 comparisons. Such a relationship does not accurately describe a CCN closure; however, it is consistent with our measurements that high CCN concentrations are more influenced by anthropogenic sources, which are less CCN active. While other CCN closures have obtained results closer to the expected 1:1 relationship, the different aerosol types (and presumably differences in aerosol chemistry) are responsible for the discrepancy. The measured N CCN at 0.3% supersaturation (S c ) ranged from 20 cm À3 (pristine) to 350 cm À3 (anthropogenic) with an average of 106 ± 54 cm À3 over the experiment. The inferred supersaturation in the clouds sampled during this experiment is $0.3%. CCN concentrations of cloud-processed aerosol were well predicted using an ammonium sulfate approximation for S c 0.4%. Predicted N CCN for other aerosol types (i.e., Asian and North American aerosols) were high compared to measured values indicating a less CCN active aerosol. This study highlights the importance of chemical effects on CCN measurements and introduces a CCN activation index as a method of classifying the efficiency of an aerosol to serve as CCN relative to an ammonium sulfate particle. This index ranged from close to unity for cloud processed aerosols to as low as 0.31 for aged aerosols transported from Asia. We also compare the performance of two CCN instruments (static thermal diffusion chamber and streamwise continuous flow chamber) on a 45 minute level leg where we observe an aged layer and a nucleation event. More than 50% of the aged aerosol served as CCN at 0.2% S c , primarily owing to their large size, while CCN concentrations during the nucleation event were close to 0 cm À3 . CCN concentrations from both instruments agreed within instrument errors; however, the continuous flow chamber effectively captured the rapid transition in aerosol properties.

[1] Several recent studies have reported a substantial correlation between satellite retrievals of aerosol optical depth (AOD) and cloud fraction, which is ascribed to an aerosol microphysical mechanism. Another possible explanation, however, is that the history of meteorological forcing controls both AOD and cloud fraction. The present study examines the latter hypothesis by comparing meteorological conditions along parcel back-trajectories for cases of large and small AOD and cloud fraction. Cloud and aerosol observations are obtained from the MODIS instrument aboard Terra, and meteorological information is obtained from ECMWF analyses. For continuity with previous investigations, the analysis focuses on the stratocumulus cloud region of the Northeast Atlantic during June through August 2002, the season of maximum cloud cover. Results show that scenes with large AOD and large cloud fraction had origins closer to Europe and experienced greater lower tropospheric static stability (LTS) during the past 2 -3 days than did scenes with small AOD and small cloud fraction. Controlling for variations in LTS reduces the dependence of cloud fraction on AOD by at least 54%. We conclude that meteorological forcing must be accounted for in assessing aerosol impacts on cloud forcing, and that doing so requires a Lagrangian analysis of parcel histories.