ABSTRACT The sensitivity of winter recreation to climate change, especially to warming, is widely recognized but few studies report quantitatively on the observed effects of climate change on ski resorts, in part because consistent and available data directly from ski resorts is scarce. Augmenting strictly modelling‐based studies, we use both numerical modelling and observation‐based estimates of sensitivity in snow depth (HS) and snow water equivalent (SWE) to temperature and precipitation using data from nearby SNOTEL (snow telemetry) and snow course sites for 40 ski resorts in Washington, Idaho, Oregon and California during the ski season. Multiple regression on climate variables then permits statistical projections of future snow depth from projected changes in temperature and precipitation with 20 future climate scenarios (10 global climate models and 2 emissions scenarios, RCP4.5 and RCP8.5). We also use projected future SWE from a hydrology model with climate input from the same 20 climate scenarios. The two methods produce substantially different projected changes at individual resorts but in aggregate the distributions are similar, leading to these broad conclusions: While many resorts indeed face substantial declines in ski‐season snow depth, many of those in the inland Northwest and a few at high elevation are likely to be minimally affected. Mitigating factors include (a) projected increases in winter precipitation over the Rockies that partly offset the effects of warming; (b) low temperature sensitivity at those locations and over high altitudes; (c) lower observed declines and temperature sensitivity for snow in winter compared with spring; and (d) many ski resorts are located in areas of high snowfall and/or span a considerable range of elevations.

Abstract. Winter recreation’s vulnerability to climate change, especially to warming, is widely recognized but few studies report quantitatively on the observed effects of climate change on ski resorts, in part because consistent and available data directly from ski resorts is scarce. Instead, we use proxy data from nearby SNOTEL (snow telemetry) and snow course sites to examine sensitivity of snow depth (HS) and snow water equivalent (SWE) to temperature and precipitation at 41 select ski resorts in Washington, Idaho, Oregon, and California, during the ski season. Multiple regression on climate variables then permits statistical projections of future snow depth from projected changes in temperature and precipitation. We also use projected future SWE from a hydrology model with climate input from CMIP5 models with the RCP4.5 and RCP8.5 scenarios to evaluate future changes in snow depth at the selected ski resorts. While many resorts indeed face substantial declines in ski-season snow depth, many of those in Idaho and a few at high elevation are likely to be minimally affected. Mitigating factors include (a) projected increases in winter precipitation over the Rockies that partly offset the effects of warming; (b) low temperature sensitivity there and over high altitudes; (c) lower observed declines and temperature sensitivity for snow in winter compared with spring; and (d) many ski resorts are located in areas of high snowfall and/or span a considerable range of altitudes.

The area burned in the western United States during the 2020 fire season was the greatest in the modern era. Here we show that the number of human‐caused fires in 2020 also was elevated, nearly 20% higher than the 1992–2019 average. Although anomalously dry conditions enabled ignitions to spread and contributed to record area burned, these conditions alone do not explain the surge in the number of human‐caused ignitions. We argue that behavioral shifts aimed at curtailing the spread of COVID‐19 altered human‐environment interactions to favor increased ignitions. For example, the number of recreation‐caused wildfires during summer was 36% greater than the 1992–2019 average; this increase was likely a function of increased outdoor recreational activity in response to social distancing measures. We hypothesize that the combination of anomalously dry conditions and COVID‐19 social disruptions contributed to widespread increases in human‐caused ignitions, adding complexity to fire management efforts during the 2020 western US fire season. Knowledge of how social behavior changes indirectly contributed to the increased number of ignitions in the 2020 wildfire season can help inform resource management in an increasingly flammable world.

In late June 2021, multiple days of record-breaking heat caused an unprecedented amount of foliage death in the forests of the Pacific Northwest, USA. Portions of tree canopies with healthy green foliage prior to the heat changed to red or orange shortly after the event. The change in foliage color could be readily seen in satellite imagery and was corroborated as foliar death (heat scorch) by aerial surveys and extensive observations on the ground. To better understand the patterns and processes driving foliar death, we used satellite imagery to identify 293,546 ha of forest, or ~4.7% of forest area, that were damaged in western Oregon and Washington by this extreme heat event. Analysis of underlying drivers of the observed heat damage indicated greater sensitivity was related to abiotic factors such as sun exposure, aspect, and microclimate, as well as biotic factors like tree species and stand age, budburst phenology, and foliar pathogens impacting tree health. Iconic, culturally and economically significant species like western redcedar, western hemlock, and Sitka spruce were disproportionately sensitive to heat damage, including in old-growth stands where they are canopy dominants. These findings highlight the multifaceted challenges posed to forests by extreme heat waves, and the need to better understand their impact on forest ecosystems in a rapidly warming climate.

Due to the difficulties of gathering relevant data of groundwater systems and the lack of fundamental physically-based understanding on the processes involved, the representation of groundwater flow heterogeneity in catchment- to regional-scale hydrological models is often overlooked. We often limit the representation of groundwater with simplified homogeneous and shallow aquifers where effective hydraulic properties are derived from global-scale database. This raises questions regarding the validity of such models to quantify the potential impacts of climate change, where subsurface heterogeneity is expected to play a major role in their short- to long- term regulation. We will present the results of a numerical modelling experiment designed to explore the role of the vertical compartmentalization of hillslopes on groundwater flow and recession discharge. We found that, when hydraulic properties are vertically compartmentalized, streamflow recession behaviour may strongly deviate from what is predicted by groundwater theory that considers the drainage of shallow reservoirs with homogeneous properties. We further identified the hillslope configurations for which the homogeneous theory derived from the Boussinesq solution approximately holds and, conversely, for those for which it does not. By comparing the modelled streamflow recession discharge and the groundwater table dynamics, we identify the critical hydrogeological conditions responsible for the emergence of strong deviations. We further present new solutions to better represent subsurface heterogeneity in catchment-scale models and calibrate hydraulic parameters that properly capture the groundwater and streamflow dynamics.

We synthesized more than 70 articles, most peer reviewed, that addressed the heat wave that occurred across the Pacific Northwest of the United States and Canada in late June 2021, breaking hundreds of daily and all-time daily maximum temperature records across the region. A persistent, extraordinarily strong ridge of high pressure was a primary driver of the heat wave. Contributing mechanisms were moisture originating in the tropical western Pacific Ocean, high solar radiation, low pressure offshore, large-scale subsidence over land, and unusually dry soils. Climate change contributed to the heat wave's magnitude by increasing mean temperature, although it is unclear whether the trend in extreme temperature is steeper than the trend in mean temperature. Mortality, heat-induced illness, and the number of visits to emergency departments during the 2021 heat wave were anomalously high. Individual and compounded social determinants of adverse outcomes included older age, living alone, lower income, and lack of functioning air conditioning. Browning or scorch of tree leaves and needles following the heat wave was exten-sive, although the extent of long-term tree mortality is not yet clear. Following the heat wave, Oregon, Washington, and British Columbia established new regulations and programs to reduce the risk of heat-related illness in the workplace. It is not yet feasible to rigorously evaluate the effectiveness of these new initiatives. SIGNIFICANCE STATEMENT: We synthesized more than 70 publications that addressed the causes and consequences of the extreme heat wave across the Pacific Northwest of the United States and Canada in late June 2021 and the potential for similar future heat waves. Interest in the heat wave among scientists, policymakers, and the public continues to be intense. Climate change contributed to the heat's magnitude, and many publications indicated that a similarly intense heat wave was extremely unlikely prior to the Industrial Revolution. Mortality and heat-induced illness during the heat wave were anomalously high, especially among older adults. Extensive scorch of tree leaves and needles followed the heat wave. In response to the heat wave, Oregon, Washington, and British Columbia established new protective regulations.

Red fl ag warnings (RFWs) are issued by the U.S. National Weather Service to alert fi re and emergency response agencies of weather conditions that are conducive to extreme wildfire growth. Distinct from most weather warnings that aim to reduce exposure to anticipated hazards, RFWs may also mitigate hazards by reducing the occurrence of new ignitions. We examined the efficacy of RFWs as a means of limiting human-caused wildfire ignitions. From 2006 to 2020, approximately 8% of wildfires across the western United States and 19% of large wildfires (>= 40 ha) occurred on days with RFWs. Although the occurrence of both lightning- and human-caused wildfires was elevated on RFW days compared to adjacent days without RFWs, we found evidence that modification of short-term behavioral choices on RFW days may reduce the number of certain human-caused ignitions (e.g., debris burning). By contrast, there is limited historical evidence that RFWs reduce the number of ignitions caused by habitual behaviors (e.g., smoking) or infrastructure (e.g., power lines). Furthermore, the conditional probability of a human-caused wildfire becoming a large wildfire was 33% greater on days with RFWs, underscoring the value of wildfire prevention on these days. While RFWs are helpful in certain cases, our results suggest that their efficacy as a wildfire prevention measure has been somewhat limited in the western United States. As the biophysical wildfire potential and the density of people living in wildfire-prone areas increase, so do the benefits of improved wildfire early warning systems that complement other wildfire mitigation and adaptation efforts.

The 2015 Sustainable Development Goals (SDGs) provide a set of aspirational objectives for the world, addressing interlinked themes including poverty, hunger, and climate action. Meeting these goals requires a similarly integrated and interdisciplinary approach. One component of such an approach may be agrivoltaic systems (AVS): dual use solar and agricultural systems wherein crops are grown beneath and between solar panels. Given their intersectoral nature, AVS will have complex impacts on the achievement of the SDGs. This analysis seeks to evaluate how AVS could impact progress towards the SDGs based on literature around the impacts of agriculture, solar, and AVS, and the indicators measuring progress towards the SDGs. It uses a Strengths, Weaknesses, Opportunities, and Threats (SWOT) framework and applies it in a unique way to understand the direct and immediate impacts to the SDGs following the installation of an AVS (i.e., strengths and weaknesses), and the potential impacts on the SDGs based on secondary or supplementary actions taken once an AVS is installed (i.e., opportunities and threats). Though the most obvious of AVS' impacts to the SDGs will be on Goals 2 (Zero Hunger) and 7 (Affordable and Clean Energy), evaluation of individual indicators shows that AVS can quantifiably impact 14 out of 17 SDGs, largely in a positive manner. However, evaluating impacts on the SDGs indicator by indicator also reveals possible negative, and unexpected, consequences of AVS. Yet, impacts on the SDGs will vary by location-specific factors such as climate, and so this analysis concludes with an application of the SWOT framework in Ethiopia for a farm where an AVS is under consideration. Altogether, this work should provide a means for evaluating the impacts of AVS on SDGs and insights into how to mitigate possible detrimental impacts while capitalizing on benefits.

Little is known about the effect of future weather and climate on municipal water demand in coastal communities with tourist-centric economies. To address this knowledge gap, we used an econometric model of monthly water demand that allowed for non-linear responses to weather variables to estimate temperature-response functions for demand from a sample of communities in the Oregon Mid-Coast. A main result is that local temperature was not a significant driver of variability in monthly water demand but that temperature in the Willamette Valley – the source of most tourists to the Oregon coast – was. We assumed that the increase in demand in response to higher Willamette Valley temperature arose from an increase in tourists escaping the heat in the Willamette Valley for cooler conditions on the coast. Applying the temperature response functions to scenarios of future climate to the year 2070 led to projected increases in water demand independent of other factors. Whether future tourism is either constrained by the local resident population that serves tourism or is constrained by the potential tourist population in the Willamette Valley, the climate-change contribution to projected water demand is generally of comparable magnitude to – if not greater than – the contribution from resident population change alone over the next fifty years. For communities where the population is projected to decline, the climate effect may more than offset the effect of declining population, resulting in a net positive change in demand.

Journal Article Causes of widespread foliar damage from the June 2021 Pacific Northwest Heat Dome: more heat than drought Get access C J Still, C J Still Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA Corresponding author (chris.still@oregonstate.edu) https://orcid.org/0000-0002-8295-4494 Search for other works by this author on: Oxford Academic PubMed Google Scholar A Sibley, A Sibley Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar D DePinte, D DePinte US Department of Agriculture, Forest Service, Pacific Northwest Region, State & Private Forestry, Forest Health Protection, Redmond, OR 97756, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar P E Busby, P E Busby Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar C A Harrington, C A Harrington US Department of Agriculture, Forest Service, Pacific Northwest Research Station, Olympia, WA 98512, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar M Schulze, M Schulze Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar D R Shaw, D R Shaw Department of Forest Engineering, Resources, and Management, Oregon State University, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar D Woodruff, D Woodruff US Department of Agriculture, Forest Service, Pacific Northwest Research Station, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar D E Rupp, D E Rupp Oregon Climate Change Research Institute, College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar C Daly, C Daly PRISM Climate Group, Northwest Alliance for Computational Science and Engineering, Oregon State University, Corvallis, OR 97331, USA Search for other works by this author on: Oxford Academic PubMed Google Scholar ... Show more W M Hammond, W M Hammond Agronomy Department, University of Florida, Institute of Food and Agricultural Sciences, Gainesville, FL 32611, USA https://orcid.org/0000-0002-2904-810X Search for other works by this author on: Oxford Academic PubMed Google Scholar G F M Page G F M Page Biodiversity and Conservation Science, Department of Biodiversity, Conservation and Attractions, Locked Bag 104, Bentley Delivery Centre, Bentley, Western Australia 6983, AustraliaCSIRO Land and Water, Private Bag 5, Wembley, Western Australia 6913, Australia Search for other works by this author on: Oxford Academic PubMed Google Scholar Tree Physiology, Volume 43, Issue 2, February 2023, Pages 203–209, https://doi.org/10.1093/treephys/tpac143 Published: 05 January 2023 Article history Received: 08 June 2022 Accepted: 11 December 2022 Published: 05 January 2023 Corrected and typeset: 17 January 2023

In Washington, Oregon, and California, ignitions from recreational activities accounted for 12% of human-caused wildfires, and 8% of the area burned, from 1992–2020. Wildfires ignited by recreational activities not only increase fire suppression expenditures but have the potential to limit recreational activities traditionally associated with use of fire, such as camping. From 1992–2020, 50% of recreation-caused ignitions in these three states occurred on lands managed by the U.S. Forest Service. The mean annual number of recreation-caused ignitions on national forests in the three states during this period was relatively stable, about 500, whereas recreation-caused ignitions within other jurisdictions decreased by 40%. Improved understanding of the impact of human and climatic factors on recreation-caused ignitions could provide valuable insights for shaping policy and management decisions. We found that mean annual densities of recreation-caused ignitions on national forests were 7 times greater within 1 km of designated campgrounds than >1 km from campgrounds, although 80% of recreation-caused ignitions occured >1 km from designated campgrounds. Ignition density in campgrounds increased non-linearly with overnight visitor density; a doubling of visitor density was associated with a ∼40% increase in ignitions. Large (≥4 ha) recreation-caused wildfires, especially those ignited in designated campgrounds, tended to occur concurrent with drought and 1–2 years after anomalously wet conditions. These results suggest that accounting for drought in implementation of fire restrictions, and targeting wildfire-prevention awareness to recreational users outside designated campgrounds, might reduce the likelihood of recreation-caused ignitions.

Topographically channeled winds such as gap winds can be key drivers of freezing rain and ice accretion. Understanding the effect of these winds on the response of freezing rain and ice accretion to global warming is challenging because the spatial resolution of global, and most regional, climate models is too coarse to accurately simulate these winds. To examine the effect of global warming in a region influenced by strong gap winds (the northern Willamette Basin, Oregon, United States), we used 13 year retrospective and pseudo-global warming simulations from a high-resolution, convection-permitting climate model capable of reproducing the easterly gap winds through the Columbia River Gorge. We compared results from the high-resolution model to those from a large ensemble of simulations generated with a coarser-resolution climate model without a well-defined Gorge. Generally, the future projected occurrence of freezing rain decreased at lower elevations and increased at higher elevations. Easterly, low-level winds that bring cold air into the basin were stronger during projected future freezing rain because in a warmer climate, weaker easterly winds were less likely to decrease the basin’s near-surface air temperatures to sub-freezing. Because of the stronger gap winds, more of the projected ice events had longer durations and accreted more ice, even at low elevations downwind of the Gorge. The coarser resolution model also projected stronger easterly winds during freezing rain, which implies that the necessity for stronger easterly winds during future freezing rain is not limited to the gap winds but is a regional, if not more widespread.

This dataset supports the analysis in Rupp et al. (2022). The dataset consists of 17,223 data files containing the water year (WY) maximum of the daily-averaged precipitation rate simulated with the HadRM3p regional climate model configured for the western United States. Each file contains the WY maxima across the model domain for a single WY, single model parameterization, and single set of initial conditions. Please refer to Hawkins et al. (2019) and Rupp et al. (2022) for a description of how the climate model data were generated.

We used numerical modelling to explore the role of the vertical compartmentalization of hillslopes on groundwater flow and recession discharge. We found that, when hydraulic properties are vertically compartmentalized, streamflow recession behaviour may strongly deviate from what is predicted by groundwater theory that considers the drainage of shallow reservoirs with homogeneous properties. We further identified the hillslope configurations for which the homogeneous theory derived from the Boussinesq solution approximately holds and, conversely, for those for which it does not. By comparing the modelled recession discharge Q and the groundwater table dynamics, we identified the critical hydrogeological conditions controlling the emergence of strong deviations. The three main controls are (i) the contribution of a deep aquifer connected to the stream, (ii) the heterogeneity in hydraulic properties, and (iii) the slope of the interface between a shallow permeable compartment and deep bedrock one with lower hydraulic properties. Our results confirm that a correct physical interpretation of the recession discharge exponent b from the classical equation -dQ/dt = aQ(b), and its temporal progression, requires knowledge of the structural configuration and heterogeneity of the aquifer.

Extreme wind‐driven autumn wildfires are hazardous to life and property, due to their rapid rate of spread. Recent catastrophic autumn wildfires in the western United States co‐occurred with record‐ or near‐record autumn fire weather indices that are a byproduct of extreme fuel dryness and strong offshore dry winds. Here, we use a formal, probabilistic, extreme event attribution analysis to investigate the anthropogenic influence on extreme autumn fire weather in 2017 and 2018. We show that while present‐day anthropogenic climate change has slightly decreased the prevalence of strong offshore downslope winds, it has increased the likelihood of extreme fire weather indices by 40% in areas where recent autumn wind‐driven fires have occurred in northern California and Oregon. The increase was primarily through increased autumn fuel aridity and warmer temperatures during dry wind events. These findings illustrate that anthropogenic climate change is exacerbating autumn fire weather extremes that contribute to high‐impact catastrophic fires in populated regions of the western US.

Mountain breezes, including katabatic and anabatic flows, and temperature inversions are common features of forested mountain landscapes. However, the effects of mountain breezes on moisture transport in forests and implications for regional climate change are not well understood. A detailed, instrumented study was conducted from July to September 2012 in an even‐aged conifer forest in the Oregon Cascade Range to investigate how temperature profiles within the forest canopy influenced atmospheric surface layer processes that ventilate the forest. Subcanopy inversion strength has a bimodal relationship to subcanopy wind speed and moisture flux from the forest. On days with relatively modest heating of the top of the canopy and weak subcanopy inversions, above canopy winds more efficiently mix subcanopy air, leading to greater than average vertical moisture flux and weaker than average along‐slope, subcanopy water vapor advection. On days with strong heating of the top of the canopy and a strong subcanopy inversion, vertical moisture flux is suppressed, and daytime downslope winds are stronger than average under the canopy. Increased downslope winds lead to increased downslope transport of water vapor, carbon dioxide, and other scalars under the canopy. Increasing summer vapor pressure deficit in the Pacific Northwest will enhance both processes: vertical moisture transport by mountain breezes when subcanopy inversions are weak and downslope water vapor transport when subcanopy inversions are strong. These mountain breeze dynamics have implications for climate refugia in forested mountains, forest plantations, and other forested regions with a similar canopy structure and regional atmospheric forcings.

The exponential growth in solar radiation measuring stations across the conterminous United States permits the generation of gridded solar irradiance data that capture the spatio-temporal variability of solar irradiance far more accurately than previously possible from ground-based observations. Taking advantage of these observations, we generated a 30-year climatology (1991-2020) of mean monthly global irradiance at a resolution of 30 arcsec (∼800 m) on both a horizontal and sloped ground surface. This paper describes the methods used to generate the gridded data, which include extensive quality control of station data, spatial interpolation of effective cloud transmittance using the “PRISM” method, and simulation of the effects of elevation, shading, and reflection from nearby terrain on solar irradiance. A comparison of the new dataset to several other solar radiation products reveals some spatial features in solar radiation that are either lacking or under-resolved in some or all of the other datasets. Examples of these features include strong gradients near foggy coastlines and along mountain ranges where there is persistent orographically driven cloud formation. The workflow developed to create the long-term means will be used as a template for generating time series of monthly and daily solar radiation grids up to the present.

Cold-air drainage and pooling can have wide-ranging impacts, including affecting ecosystem processes and agricultural crops, and contributing to decreased air quality associated with temperature inversions. Future climate changes may alter both the frequency and intensity of cold-air drainage. This study estimates the response of nocturnal cold-air drainage to warming resulting from anthropogenic greenhouse gases, specifically CO 2 , considering radiative and thermodynamic effects but not changes in background air flow (dynamic effects). A simple index is proposed to represent the propensity for clear-sky nocturnal cold-air drainage as a function of air temperature and humidity near dusk. Decreases in this index with increasing atmospheric emissivity due to increasing anthropogenic greenhouse gase concentrations imply a weakening of cold-air drainage. The magnitude of the decrease in the index is positively related to the initial background temperature and humidity: Warm regions are more sensitive than cold regions, and humid regions are more sensitive than dry regions, implying that warm and/or humid regions are more at risk of decreases in cold-air drainage. Under atmospheric CO 2 concentrations consistent with Representative Concentration Pathway (RCP) 8.5, the magnitude of decrease in the index indicates that nocturnal cold-air drainage intensity may decline by at least 10% by 2100 CE (compared to 1979–1990) with larger decreases in warm and humid regimes. The index should be tested with intentionally designed field or lab experiments, and the relative effects on cold-air drainage of changes in radiative, sensible, and latent heat fluxes, and atmospheric circulation, should be compared.

The United States (U.S.) West Coast power system is strongly influenced by variability and extremes in air temperatures (which drive electricity demand) and streamflows (which control hydropower availability). As hydroclimate changes across the West Coast, a combination of forces may work in tandem to make its bulk power system more vulnerable to physical reliability issues and market price shocks. In particular, a warmer climate is expected to increase summer cooling (electricity) demands and shift the average timing of peak streamflow (hydropower production) away from summer to the spring and winter, depriving power systems of hydropower when it is needed the most. Here, we investigate how climate change could alter interregional electricity market dynamics on the West Coast, including the potential for hydroclimatic changes in one region (e.g., Pacific Northwest (PNW)) to “spill over” and cause price and reliability risks in another (e.g., California). We find that the most salient hydroclimatic risks for the PNW power system are changes in streamflow, while risks for the California system are driven primarily by changes in summer air temperatures, especially extreme heat events that increase peak system demand. Altered timing and amounts of hydropower production in the PNW do alter summer power deliveries into California but show relatively modest potential to impact prices and reliability there. Instead, our results suggest future extreme heat in California could exert a stronger influence on prices and reliability in the PNW, especially if California continues to rely on its northern neighbor for imported power to meet higher summer demands.

Abstract. The US and Canada have entered negotiations to modernize the Columbia River Treaty, signed in 1961. Key priorities are balancing flood risk, hydropower production, and improving aquatic ecosystem function while incorporating projected effects of climate change. In support of the US effort, Chegwidden et al. (2017) developed a large-ensemble dataset of past and future daily flows at 396 sites throughout the Columbia River Basin (CRB) and select other watersheds in western Washington and Oregon, generating a large ensemble using state-of-the art climate and hydrologic models. In this study, we use that dataset – the largest now available – to present new analyses of the effects of future climate change on flooding using water year maximum daily flows. For each simulation, flood statistics are estimated from Generalized Extreme Value distributions fit to simulated water year maximum daily flows for 50-year windows of the past (1950–1999) and future (2050–2099) periods. Our results contrast with previous findings: we find that the vast majority of locations in the CRB are estimated to experience an increase in future discharge magnitudes. We show that on the Columbia and Willamette rivers, increases in discharge magnitudes are smallest downstream and grow larger moving upstream. For the Snake River, however, the pattern is reversed, with increases in discharge magnitudes growing larger moving downstream to the confluence with the Salmon River tributary, and then abruptly dropping. We decompose the variation in results attributable to climate and hydrologic factors, finding that climate contributes more variation in larger basins while hydrology contributes more in smaller basins. Equally important for practical applications like flood control rule curves, the seasonal timing of flooding shifts dramatically on some rivers (e.g., on the Snake, 20th century floods occur exclusively in late spring, but by the end of the 21st century some floods occur as early as December) and not at all on others (e.g. the Willamette).