Columbia River Basin Research Articles

Reach‐scale stream temperature response to large wood placement

Climate change models indicate that stream temperatures within much of the Columbia River Basin will increase significantly in the next 50 years leading to inhospitable conditions for salmonid fishes in several stream reaches. Restoration measures such as riparian planting, maintaining instream flows, and large wood (LW) placement are thought to ameliorate the impacts of climate change on stream temperatures. While LW placement is known to improve habitat complexity, it is unclear whether it will also help reduce summer stream temperatures. To help understand the influence of LW placement on stream temperatures, we monitored nine interior Columbia River Basin LW projects using an extensive posttreatment study design. We mapped stream bottom temperatures, topography, and physical habitat in paired treatment (LW placement) and control reaches to compare water temperatures and cool‐water patches between reaches. We found no difference in the mean or the variance in overall reach temperatures or thalweg temperatures between treatment and control reaches. Mapping found variation in water temperatures of less than 0.5°C within reaches, making mapping of cool‐water patches impractical and further emphasized the lack of temperature differences. Our results indicate that LW placement projects in the interior Columbia River Basin do not appear to be decreasing reach‐scale summer water temperatures or creating cool water refugia for fishes. Moreover, the current configuration and implementation of LW placement projects, which typically focus on placing wood on banks and channel margins, are unlikely to ameliorate the effects of climate change on stream temperatures.

Dietary tetradecylthioacetic acid supplementation during the fall prevents an increase in body lipid levels but does not influence precocious male maturation rate in juvenile spring Chinook salmon

Precocious maturation of male fish as two-year-olds occurs at significant rates in spring Chinook salmon hatchery programmes in the Columbia River Basin, representing a loss of production. Precocious maturation is thought to occur due to elevated lipid and other energy reserves in hatchery fish during critical periods for the regulation of gonadal development. To determine whether modification of lipid reserves affects precocious maturation rates in juvenile spring Chinook salmon, we administered feed supplemented with tetradecylthioacetic acid (TTA; a supplement that upregulates lipid oxidation) during the fall critical period one year prior to maturation of precocious individuals. Maturation status was determined the following spring from plasma 11-ketotestosterone levels. TTA administration reduced body lipid levels relative to controls but did not reduce precocious maturation rate. Fish growth was reduced during the TTA feeding period but recovered after fish were returned to a standard diet. No differences in the effect of TTA were found between male and female fish. Our results show that TTA can be used to manipulate body lipid levels in juvenile Chinook salmon but provide no support for a major role of fall body lipid levels in regulating precocious maturation in juvenile male spring Chinook salmon under hatchery conditions.

Tui Chub (Siphateles bicolor) are Native to the Columbia River Basin in Washington State

Although many modern authorities hold that Tui chub (Siphateles bicolor) are native to the Columbia River basin, they are uncommon in most of the basin today, and others have called their native status into question. Here we provide evidence that the species is indigenous to lakes and streams in the Columbia River basin of Washington State, based on multiple lines of testimony. Evidence includes: 1) no record of introductions by federal or state fish and wildlife management agencies; 2) over 100 museum specimens collected from 1881 to 1930; 3) records of abundance in the tens of thousands in area lakes prior to modern management efforts in the 1940s; and 4) 62 diagnostic bones recovered from four archaeological sites dating before 1850.

Ingestion of PIT Tags by Hatchery‐Reared Juvenile Steelhead and Subsequent Detection at Main‐Stem Dams in the Columbia River Basin

AbstractDuring the past 30 years, millions of hatchery‐reared Pacific salmon Oncorhynchus spp. have been implanted with PIT tags to estimate their survival and track their migration through the extensive system of hydroelectric dams in the Columbia River basin. The mark–recapture models that are used for these analyses assume that the tags are not lost, making it important to understand retention rates for PIT tags and the fate of shed tags. To understand the potential fate of shed PIT tags in a production hatchery, we distributed 12‐mm PIT tags in two traditional cement raceways and the two circular tanks of a partial reuse aquaculture system (PRAS) containing juvenile summer steelhead O. mykiss. We then monitored the detection of these PIT tags at the time that the fish were released as smolts and at main‐stem dams during their migration. The probability that a loose PIT tag was inside a steelhead smolt at release ranged from 0.200 to 0.519 across the raceways and tanks, confirming that the fish consumed tags during hatchery rearing. Detections at six dams—including one located 1,208 km from the release site—and up to 36 d after smolt release confirmed that some ingested tags remained in the steelhead during their migration. The estimates of apparent survival for smolts with ingested and implanted PIT tags suggested that some ingested tags were being excreted during migration through the Columbia River basin. The results highlight the need to reevaluate assumptions about the fate of shed PIT tags in steelhead production hatcheries and ensure that biologists and managers have reliable estimates of tag retention.

Implications of the Thermodynamic Response of Soil Mineralization, Respiration, and Nitrification on Soil Organic Matter Retention.

Considerable research has shown that modifications in global temperature regimes can lead to changes in the interactions between soil respiration and the sequestration of C and N into soil organic matter (SOM). We hypothesized that despite the interconnected nature of respiration, net N mineralization, and nitrification processes, there would be differences in their thermodynamic responses that would affect the composition of inorganic soil N and the potential for retention of N in SOM. To test this hypothesis, soil respiration, N mineralization and nitrification responses were evaluated during constant temperature incubations at seven temperatures (4–42°C) in tilled and no-till soils from two major agroecological zones in Oregon; Willamette Valley, and Pendleton located in the Columbia River Basin. We observed (1) significant thermodynamic differences between the three processes in all soils, (2) a distinctly different thermodynamic profile in Willamette vs. Pendleton, and (3) a dynamic response of Topt (optimal temperature for activity), and Tsmax (temperature of greatest rate response to temperature), and temperature sensitivity (Δ) over the incubation time course, resulting in shifts in the thermodynamic profiles that could not be adequately explained by changes in process rates. We found that differences in contributions of ammonia oxidizing archaea and bacteria to nitrification activity across temperature helped to explain the thermodynamic differences of this process between Willamette and Pendleton soils. A two-pool model of SOM utilization demonstrated that the dynamic thermodynamic response of respiration in the soils was due to shifts in utilization of labile and less-labile pools of C; and that the respiration response by Pendleton soils was more dependent upon contributions from the less-labile C pool resulting in higher Topt and Tsmax than Willamette soils. Interestingly, modeling of N mineralization using the two-pool model suggested that only the less-labile pool of SOM was contributing to N mineralization at most temperatures in all soils. The difference in labile and less-labile SOM pool utilization between respiration and N mineralization may suggest that these processes may not be as interconnected as previously thought.

Passage and Survival of Juvenile Salmonid Smolts through Dams in the Columbia and Snake Rivers, 2010–2018

AbstractMinimizing the mortality and migration time of juvenile salmon (smolts) that pass through dams is a long‐standing objective in the pursuit of salmon recovery in the Columbia River basin. We compiled and analyzed 40 acoustic tag studies of juvenile salmonid that were performed between 2010 and 2018 at seven of the eight hydroelectric projects in the Federal Columbia River Power System. We found that the use of nonturbine routes decreased monotonically moving downstream from the Snake River to the main‐stem Columbia River dams and associated mortality differed substantially between the dams in the two rivers. Spillways were the predominant passage route at the main‐stem Columbia River dams. In contrast, passage was more common through the surface weirs and juvenile bypass systems at the dams in the Snake River, which generally provided higher survival. The observed stocks exhibited variable passage behaviors and mortalities, and the estimated probability that an individual would pass through all eight dams in the system without using a turbine route was 0.31, 0.47, and 0.60 for subyearling Chinook Salmon Oncorhynchus tshawytscha, yearling Chinook Salmon, and steelhead O. mykiss, respectively. Although subyearling Chinook Salmon were generally more likely to pass through a turbine route, they also experienced less turbine‐associated mortality than did the other stocks, especially steelhead. Notably, the proportion of smolts that passed through the spillway relative to the proportion of water through the spillway was lowest at Bonneville Dam, the largest and lowermost dam in the system. Bonneville Dam also stood out as having the highest proportion of smolts passing through turbines, but it was among the locations with the lowest rates of turbine‐associated mortality.

Modeling riparian species occurrence from historical surveys to guide restoration planning in northwestern USA

AbstractSuccessful restoration of riparian habitats and functions depends in part on selection of plant species that are suited to local geomorphic and climatic conditions, which often relies on contemporary reference sites to characterize target riparian vegetation communities. In heavily modified landscapes, a lack of undisturbed sites hinders the description of reference conditions to help guide planning efforts. In lieu of contemporary reference sites, we used historical Public Land Survey data from the late 1800s and early 1900s to document historical streamside vegetation at 1685 sites distributed throughout the Columbia River basin. We used those data to construct a random forest classification model using climatic and geomorphic variables to predict the probability of occurrence of riparian vegetation groups (conifer, deciduous, shrub, and willow) and individual taxa (fir, pine, cedar, cottonwood, alder, sagebrush) for all stream reaches with bankfull width >6 m in the interior Columbia River basin. The most common predictor variables included in the best models for vegetation groups or individual taxa were mean annual precipitation, minimum temperature, elevation, and bankfull width. For some taxa, temperature range and floodplain width were also important predictors. The probability maps indicate that riparian zones were likely dominated by willow species in semi‐desert regions and by conifer species in the humid mountain regions. Deciduous species dominated riparian areas in transition zones between conifer forests and semi‐deserts. Species distributions suggest that streams in the semi‐deserts were likely characterized by little shade and low wood abundance, whereas streams in the humid mountains would have been more heavily shaded with high wood abundance. The transitional deciduous areas were likely shaded with moderate wood abundance. Historical trends in air temperature and precipitation suggest relatively small changes in climate since the time of the surveys, indicating that current species ranges are likely similar to historical species ranges. Hence, these maps can be used to help identify suitable taxonomic groups and expected riparian functions for riparian restoration in the Columbia River basin, with appropriate adjustments made to site‐specific restoration designs to account for model uncertainty, future climate change, or land use constraints.

Virulence and Infectivity of UC, MD, and L Strains of Infectious Hematopoietic Necrosis Virus (IHNV) in Four Populations of Columbia River Basin Chinook Salmon

Infectious Hematopoietic Necrosis Virus (IHNV) infects juvenile salmonid fish in conservation hatcheries and aquaculture facilities, and in some cases, causes lethal disease. This study assesses intra-specific variation in the IHNV susceptibility of Chinook salmon (Oncorhynchus tshawytscha) in the Columbia River Basin (CRB), in the northwestern United States. The virulence and infectivity of IHNV strains from three divergent virus genogroups are measured in four Chinook salmon populations, including spring-run and fall-run fish from the lower or upper regions of the CRB. Following controlled laboratory exposures, our results show that the positive control L strain had significantly higher virulence, and the UC and MD strains that predominate in the CRB had equivalently low virulence, consistent with field observations. By several experimental measures, there was little variation in host susceptibility to infection or disease. However, a small number of exceptions suggested that the lower CRB spring-run Chinook salmon population may be less susceptible than other populations tested. The UC and MD viruses did not differ in infectivity, indicating that the observed asymmetric field prevalence in which IHNV detected in CRB Chinook salmon is 83% UC and 17% MD is not due to the UC virus being more infectious. Overall, we report little intra-species variation in CRB Chinook salmon susceptibility to UC or MD IHNV infection or disease, and suggest that other factors may instead influence the ecology of IHNV in the CRB.

A critical analysis of the food–energy–water nexus in the Kootenai River Basin

The paper has applied Food–Energy–Water (FEW) nexus in the Kootenai River Basin—a basin located in greater Columbia River Basin shared by Canada and USA—to explore how the institutional, stakeholders, and environmental aspects are represented within the basin. Despite the wide application of FEW nexus, the authors argue that the nexus concept has failed to capture the social dimension such as emotions within the basin. Furthermore, although the FEW nexus is a broader concept encompassing a wide range of actors, the FEW concept was unsuccessful in integrating indigenous and tribal communities into the nexus framework. Finally, the authors assert that FEW nexus should be further explored to incorporate social and environmental dimensions such as the role of various stakeholders, e.g., tribal communities, fishery, and biodiversity, into the nexus framework in the Kootenai River Basin.

Changing River Network Synchrony Modulates Projected Increases in High Flows

AbstractProjections of change in high‐flow extremes with global warming vary widely among, and within, large midlatitude river basins. The spatial variability of these changes is attributable to multiple causes. One possible and little‐studied cause of changes in high‐flow extremes is a change in the synchrony of mainstem and tributary streamflow during high‐flow extremes at the mainstem‐tributary confluence. We examined reconstructed and simulated naturalized daily streamflow at confluences on the Columbia River in western North America, quantifying changes in synchrony in future streamflow projections and estimating the impact of these changes on high‐flow extremes. In the Columbia River basin, projected flow regimes across colder tributaries initially diverge with warming as they respond to climate change at different rates, leading to a general decrease in synchrony, and lower high‐flow extremes, relative to a scenario with no changes in synchrony. Where future warming is sufficiently large to cause most subbasins upstream from a confluence to transition toward a rain‐dominated, warm regime, the decreasing trend in synchrony reverses itself. At one confluence with a major tributary (the Willamette River), where the mainstem and tributary flow regimes are initially very different, warming increases synchrony and, therefore, high‐flow magnitudes. These results may be generalizable to the class of large rivers with large contributions to flood risk from the snow (i.e., cold) regime, but that also receive considerable discharge from tributaries that drain warmer basins.

Salmon Versus Power: Dam Removal and Power Supply Adequacy

Dam removal is gaining both support and resistance in different communities and political circles in the Pacific Northwest of the United States, given its sensitive environmental and economic consequences. The Columbia River Basin (CRB) offers a unique opportunity to examine to what extent the replacement of hydroelectric dams affects reliability and adequacy of the power system given long-standing proposals to remove the four Lower Snake River dams to improve the survival of the endangered salmon species. Key results show that replacing the four dams leads to an inadequate energy supply, necessitating the need for more capacity to satisfy requirements. Although the four dams have higher nameplate capacity, they provide a much lower effective capacity. Thus, the debate about removing dams should be an opportunity for CRB managers to consider investment options in new ecosystem services and energy solutions that maintain adequate performance.

Estimation of Long-duration Maximum Precipitation during a winter season for large basins dominated by Atmospheric Rivers using a Numerical Weather Model

The Probable Maximum Precipitation (PMP) estimation for long durations during winter and spring seasons is important to develop the Probable Maximum Flood for snowmelt-driven regions since extreme floods are often characterized by snow-accumulation and snowmelt processes rather than by a single rainstorm event. Although several studies have estimated the PMP for a single storm duration, little attention has been given to the PMP estimation for long durations on the order of several months. This study proposes a new framework using a numerical weather model (NWM) to estimate the long-duration Maximum Precipitation (MP) during the winter season, which is the first part of a two-part effort to develop the PMP during the winter and spring seasons. As a demonstrative case, we estimate the MP for the 6-month winter period (October to March) for the drainage areas of Bonneville Dam (621,600 km2) and Libby Dam (23,270 km2) in the Columbia River Basin dominated by atmospheric rivers (ARs). In the proposed framework, the historical AR events are identified based on the integrated water vapor transport thresholds used in the AR category scale. The precipitation depths during the identified AR events are then maximized by simultaneously optimizing the AR position and its atmospheric moisture. Finally, the design precipitation sequence is formed by substituting each historical AR event with the corresponding maximized AR event, acting as the basis of long-duration MP. As a result, the maximum 6-month winter period accumulated basin-average precipitation depths: long-duration MP, for the drainage areas of Bonneville Dam and Libby Dam, are estimated to be 961.0 mm and 1101.7 mm, respectively. To the authors’ knowledge, this is the first study estimating the MP for long durations on the order of several months and for very large basins (above 100,000 km2) by using the NWM-based approach.

Estimating carrying capacity for juvenile salmon using quantile random forest models

AbstractEstablishing robust methods and metrics to evaluate habitat quality is critical for the recovery of endangered Pacific salmonids (Oncorhynchus spp.). A variety of modeling approaches are used for status and trend monitoring of anadromous species throughout the Pacific Northwest, USA, but current methods may fail to capture the complex relationship between fish and habitat and are often limited in predictive power beyond specific watersheds. Further, the focus on species distribution and abundance is not easily manipulated to predict carrying capacity and traditional stock‐recruitment analyses are reliant on long‐term data which are not always available. In this study, we developed a quantile random forest model to provide estimates of habitat carrying capacity for Chinook salmon (O. tshawytscha) parr during the summer months, at both the site and watershed scale. Quantile random forest models allow for the consideration of noisy data, correlated variables, and non‐linear relationships: common features in fish–habitat datasets. We leveraged Columbia Habitat Monitoring Program data to select habitat co‐variates and predict capacity at those sites. We also identified a set of globally available attributes to extrapolate capacity estimate predictions throughout wadeable streams within the Columbia River basin. Total capacity estimates for watersheds closely matched estimates from alternative fish productivity models. Carrying capacity estimates based on quantile random forest models, like those presented here, provide managers a framework to guide the identification, prioritization, and development of habitat rehabilitation actions to recover salmon populations.

Spatial and temporal changes in climate extremes over northwestern North America: the influence of internal climate variability and external forcing

Increases in the intensity and frequency of hydroclimatic extremes associated with climate change can cause significant socioeconomic problems. Assessments of projected extremes using only a limited number of general circulation model (GCM) simulations can undermine the capacity to differentiate and communicate the contribution of internal climate variability (ICV) and external forcing and result in an underestimation of associated risks. In this study, we assess the impacts of climate change on extreme temperature and precipitation and quantify the contribution of internal variability over the Columbia, Fraser, Peace and Campbell River basins in northwestern North America (NWNA). Seven GCMs that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and a large ensemble of CanESM2 model simulations (50 members) are downscaled to 1/16° spatial resolution using Bias Correction Constructed Analogues with Quantile mapping reordering version 2 (BCCAQ2). Spatial and temporal changes of climate extreme indices, representing the frequency and intensity of extreme temperature and precipitation, are assessed over the historical (1981–2010) and future (2060–2089) periods under the Representative Concentration Pathway (RCP) 8.5. The influence of ICV on the estimated trends of extreme indices is characterised. Overall, both the frequency and intensity of extreme temperature and precipitation events are projected to increase in NWNA indicating more severe dry days and wet conditions in the future. High-elevation Rocky and the Coast Mountains are at larger risks of extreme precipitation, while the Columbia basin, which already faces drought issues, is expected to experience severe dry conditions. Internal climate variability plays a significant role, particularly in the trends of precipitation-related indices. The signal to internal noise ratio analyses suggest that higher elevations experience stronger forcing signals for precipitation-based indices compared to the other regions.

Characterizing juvenile salmon predation risk during early marine residence.

Predation mortality can influence the distribution and abundance of fish populations. While predation is often assessed using direct observations of prey consumption, potential predation can be predicted from co-occurring predator and prey densities under varying environmental conditions. Juvenile Pacific salmon Oncorhynchus spp. (i.e., smolts) from the Columbia River Basin experience elevated mortality during the transition from estuarine to ocean habitat, but a thorough understanding of the role of predation remains incomplete. We used a Holling type II functional response to estimate smolt predation risk based on observations of piscivorous seabirds (sooty shearwater [Ardenna griseus] and common murre [Uria aalge]) and local densities of alternative prey fish including northern anchovy (Engraulis mordax) in Oregon and Washington coastal waters during May and June 2010–2012. We evaluated predation risk relative to the availability of alternative prey and physical factors including turbidity and Columbia River plume area, and compared risk to returns of adult salmon. Seabirds and smolts consistently co-occurred at sampling stations throughout most of the study area (mean = 0.79 ± 0.41, SD), indicating that juvenile salmon are regularly exposed to avian predators during early marine residence. Predation risk for juvenile coho (Oncorhynchus kisutch), yearling Chinook salmon (O. tshawytscha), and subyearling Chinook salmon was on average 70% lower when alternative prey were present. Predation risk was greater in turbid waters, and decreased as water clarity increased. Juvenile coho and yearling Chinook salmon predation risk was lower when river plume surface areas were greater than 15,000 km2, while the opposite was estimated for subyearling Chinook salmon. These results suggest that plume area, turbidity, and forage fish abundance near the mouth of the Columbia River, all of which are influenced by river discharge, are useful indicators of potential juvenile salmon mortality that could inform salmonid management.

Differential impacts of freshwater and marine covariates on wild and hatchery Chinook salmon marine survival.

Large-scale atmospheric conditions in the Northeast Pacific Ocean affect both the freshwater environment in the Columbia River Basin and marine conditions along the coasts of Oregon, Washington, and British Columbia, resulting in correlated conditions in the two environments. For migrating species, such as salmonids that move through multiple habitats, these correlations can amplify the impact of good or poor physical conditions on growth and survival, as movements among habitats may not alleviate effects of anomalous conditions. Unfortunately, identifying the mechanistic drivers of salmon survival in space and time is hindered by these cross-habitat correlations. To address this issue, we modeled the marine survival of Snake River spring/summer Chinook salmon with multiple indices of the marine environment and an explicit treatment of the effect of arrival timing from freshwater to the ocean, and found that both habitats contribute to marine survival rates. We show how this particular carryover effect of freshwater conditions on marine survival varies by year and rearing type (hatchery or wild), with a larger effect for wild fish. As environmental conditions change, incorporating effects from both freshwater and marine habitats into salmon survival models will become more important, and has the additional benefit of highlighting how management actions that affect arrival timing may improve marine survival.

Progress Towards a Comprehensive Approach for Habitat Restoration in the Columbia Basin: Case Study in the Grande Ronde River

Despite immense resources directed towards habitat restoration, recovering fish populations remains a daunting and perplexing issue. In 2015, recommendations for a comprehensive approach to habitat restoration in the Columbia River basin were published in Fisheries, which included elements of landscape ecology and resilience, broad public support, governance for collaboration and integration, and capacity for learning and adaptation. Using the Grande Ronde River basin as a case study, we convened a working group consisting of local restoration practitioners, managers, and researchers involved in habitat restoration research, monitoring, and evaluation to assess progress towards meeting these recommendations. We concluded that partnerships and collaborations in governance have been formed and research using a landscape perspective has been integrated into decision making, but efforts would benefit from gaining broader public support, formalizing an adaptive management strategy, and defining objectives and indicators for biological and ecological diversity. Continued progress will require consistent policy and funding support from the broader region. We envision this self‐assessment at the 5‐year milestone would be helpful to other groups facing similar challenges.

Elevated stream temperature, origin, and individual size influence Chinook salmon prespawn mortality across the Columbia River Basin

Conservation and restoration efforts for Pacific salmon Oncorhynchus spp. can be hampered by prespawn mortality, when adult fish reach reproductive sites but die before spawning. We examined annual estimates of female Chinook salmon O. tshawytscha prespawn mortality relative to individual fish traits (77,707 individual females) and reach-scale variables in 49 study reaches from 41 streams throughout the interior Columbia River Basin. Mean annual prespawn mortality estimates across 14 years ranged from 0 % to 65 %. For spring-run Chinook salmon, the probability of prespawn mortality decreased over the spawning period, was positively associated with mean August stream temperature and individual fish length, and was higher for hatchery-origin than natural-origin fish. Based on the basin-wide statistical model and future stream temperature predictions, average spring-run Chinook salmon prespawn mortality rates in 2040 were predicted to increase by 0–17 % for fish of natural origin and 1–17 % for fish of hatchery origin. Climate change is likely to exacerbate conditions that lead to prespawn mortality, particularly in low elevation stream reaches, for larger fish, and for those of hatchery origin.

Ubiquitous increases in flood magnitude in the Columbia River basin under climate change

Abstract. The USA and Canada have entered negotiations to modernize the Columbia River Treaty, signed in 1961. Key priorities are balancing flood risk and 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 streamflows at 396 sites throughout the Columbia River basin (CRB) and selected other watersheds in western Washington and Oregon, using state-of-the art climate and hydrologic models. In this study, we use that dataset to present new analyses of the effects of future climate change on flooding using water year maximum daily streamflows. For each simulation, flood statistics are estimated from generalized extreme value distributions fit to simulated water year maximum daily streamflows 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 streamflow magnitudes. The near ubiquity of increases is all the more remarkable in that our approach explores a larger set of methodological variation than previous studies; however, like previous studies, our modeling system was not calibrated to minimize error in maximum daily streamflow and may be affected by unquantifiable errors. We show that on the Columbia and Willamette rivers increases in streamflow magnitudes are smallest downstream and grow larger moving upstream. For the Snake River, however, the pattern is reversed, with increases in streamflow 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 variability in climate and hydrologic factors across the ensemble, 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 River).

Mountain waves can impact wind power generation

Abstract. Mountains can modify the weather downstream of the terrain. In particular, when stably stratified air ascends a mountain barrier, buoyancy perturbations develop. These perturbations can trigger mountain waves downstream of the mountains that can reach deep into the atmospheric boundary layer where wind turbines operate. Several such cases of mountain waves occurred during the Second Wind Forecast Improvement Project (WFIP2) in the Columbia River basin in the lee of the Cascade Range bounding the states of Washington and Oregon in the Pacific Northwest of the United States. Signals from the mountain waves appear in boundary layer sodar and lidar observations as well as in nacelle wind speeds and power observations from wind plants. Weather Research and Forecasting (WRF) model simulations also produce mountain waves and are compared to satellite, lidar, and sodar observations. Simulated mountain wave wavelengths and wave propagation speeds (group velocities) are analyzed using the fast Fourier transform. We found that not all mountain waves exhibit the same speed and conclude that the speed of propagation, magnitudes of wind speeds, or wavelengths are important parameters for forecasters to recognize the risk for mountain waves and associated large drops or surges in power. When analyzing wind farm power output and nacelle wind speeds, we found that even small oscillations in wind speed caused by mountain waves can induce oscillations between full-rated power of a wind farm and half of the power output, depending on the position of the mountain wave's crests and troughs. For the wind plant analyzed in this paper, mountain-wave-induced fluctuations translate to approximately 11 % of the total wind farm output being influenced by mountain waves. Oscillations in measured wind speeds agree well with WRF simulations in timing and magnitude. We conclude that mountain waves can impact wind turbine and wind farm power output and, therefore, should be considered in complex terrain when designing, building, and forecasting for wind farms.