Western United States Research Articles

Predicting Post-Wildfire Stream Temperature and Turbidity: A Machine Learning Approach in Western U.S. Watersheds

Wildfires significantly impact water quality in the Western United States, posing challenges for water resource management. However, limited research quantifies post-wildfire stream temperature and turbidity changes across diverse climatic zones. This study addresses this gap by using Random Forest (RF) and Support Vector Regression (SVR) models to predict post-wildfire stream temperature and turbidity based on climate, streamflow, and fire data from the Clackamas and Russian River Watersheds. We selected Random Forest (RF) and Support Vector Regression (SVR) because they handle non-linear, high-dimensional data, balance accuracy with efficiency, and capture complex post-wildfire stream temperature and turbidity dynamics with minimal assumptions. The primary objectives were to evaluate model performance, conduct sensitivity analyses, and project mid-21st century water quality changes under Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. Sensitivity analyses indicated that 7-day maximum air temperature and discharge were the most influential predictors. Results show that RF outperformed SVR, achieving an R2 of 0.98 and root mean square error of 0.88 °C for stream temperature predictions. Post-wildfire turbidity increased up to 70 NTU during storm events in highly burned subwatersheds. Under RCP 8.5, stream temperatures are projected to rise by 2.2 °C by 2050. RF’s ensemble approach captured non-linear relationships effectively, while SVR excelled in high-dimensional datasets but struggled with temporal variability. These findings underscore the importance of using machine learning for understanding complex post-fire hydrology. We recommend adaptive reservoir operations and targeted riparian restoration to mitigate warming trends. This research highlights machine learning’s utility for predicting post-wildfire impacts and informing climate-resilient water management strategies.

Assessing costs and constraints of forest residue disposal by pile burning

Pile burning of thinned residues is a critical tool to dispose of fuels and to reduce wildfire risk in overstocked, fire-prone forests globally. However, cost estimates of pile burning are limited. In the Western United States, where fuel reduction and pile burning are key strategies to mitigate risk of severe wildfire, previous reports estimate that the average cost of pile burning after machine treatment is $543 ac−1 ($1,343 ha−1). There is, however, limited information on the costs of hand thinning and pile burning. In response, this study quantified the costs of cutting and yarding, piling, and burning residues via two pathways: the USDA Forest Service (USFS) Activity Tracking System (FACTS) database, and interviews with 11 USFS fire management professionals from California, Oregon, and Washington. Interviews highlighted cost drivers, implementation constraints, and opportunities for efficiency improvements. The average costs of piling and burning machine piles as determined from the interviews were $735 ± $464 ac−1 ($1,817 ± $1,146 ha−1; all mean ± SD), 80% higher than reported in the FACTS database and 35% higher than previous reports. The average costs of piling and burning hand piles as determined from the interviews were $1,291 ± $717 ac−1 ($3,190 ± $1,722 ha−1), 135% higher than reported in the FACTS database. Interview participants reported proximity to roads and terrain as key cost drivers, and described common practices, challenges, and constraints to pile burning. Geospatial analyses supported interviewee-identified cost drivers, district road density (a proxy for accessibility) and district maximum elevation (a proxy for terrain). Simulations of direct emissions from pile burning on National Forests included in this study indicated annual emissions of 11,322 metric tons (MT) of particulate matter (PM), 8,029 MT of PM10, and 6,993 MT of PM2.5 across the study area. In addition, pile burning on these National Forests annually emits >1.7 million MT CO2, 61,515 MT of carbon monoxide, 3,823 MT of methane, and 3,211 MT of non-methane hydrocarbons. Given the economic, human health, and climate implications of current pile burning practice, removing residues as feedstocks for carbon-negative utilizations is recommended as a near-term priority. Policy mechanisms, such as feedstock production, transport, or offtake subsidies of a similar magnitude to such avoided costs, could efficiently incentivize residue removal and support such climate-positive utilizations.

Potential of long-term satellite observations and reanalysis products for characterising soil drying: trends and drought events

Abstract. Soil drying has multiple adverse impacts on the environment, society, and economy. Thus, it is crucial to monitor and characterise related drought events and to understand how underlying geophysical trends may affect them. Here, we compare the ability of long-term satellite observations and state-of-the-art reanalysis products to characterise soil drying. We consider the European Space Agency Climate Change Initiative (ESA CCI) remote-sensing surface soil moisture products (encompassing an ACTIVE, a PASSIVE, and a COMBINED product) as well as surface and root zone soil moisture from the ERA5, ERA5-Land, and MERRA-2 reanalysis products. In addition, we use a new root zone soil moisture dataset derived from the ESA CCI COMBINED product. We analyse global surface and root zone soil moisture trends in these products over the 2000–2022 period. Furthermore, we investigate the impact of the products' trend representation on their ability to capture major seasonal soil moisture (or agroecological) drought events as a use case. The latter is based on the analysis of 17 selected drought events documented in the scientific literature; these events are characterised by their severity (the time-accumulated standardised soil moisture anomalies), magnitude (the minimum of the standardised anomalies over time), duration, and spatial extent. The soil moisture trends are globally diverse and partly contradictory between products. ERA5, ERA5-Land, and ESA CCI COMBINED show larger fractions of drying trends, whereas ESA CCI ACTIVE and MERRA-2 display more widespread wetting trends. The differences between reanalysis products are related to a positive mean bias in the precipitation trends and regionally negative biases in surface air temperature trends in MERRA-2 compared with ground observational products, suggesting that this reanalysis underestimates drying trends. Given these biases in the MERRA-2 precipitation and temperature trends and considering available validation studies, the ESA CCI COMBINED-based products and ERA5-Land are considered more reliable and are consecutively used for a synthesis of global surface and root zone soil moisture trends. This synthesis suggests a consistent tendency towards soil drying during the last 2 decades in these products in 49.3 % of the surface and 44.5 % of the root zone layers of the covered global land area. The respective fractions of wetting trends amount to 21.1 % and 20.6 % for the surface and root zone, respectively, while areas with no trend direction consensus amount to 29.6 % and 35.0 %, respectively, reflecting the considerable uncertainties associated with global soil moisture trends. Geographically, drying is localised to parts of Europe and the Mediterranean; the Black Sea–Caspian Sea and Central Asian region; Siberia; parts of the western USA and the Canadian Prairies; and larger parts of South America, parts of southern and northern Africa, and parts of northwestern Australia. All investigated products mostly capture the considered drought events. Overall, the events tend to be least pronounced in the ACTIVE remote-sensing product across all drought metrics, particularly with respect to the magnitudes. Furthermore, MERRA-2 shows lower drought magnitudes than the other products, in both the surface layer and the root zone. The COMBINED remote-sensing products (surface and root zone soil moisture dataset) display partly stronger drought severities than the other products. In the root zone, the droughts are dampened with respect to the magnitude and smaller with respect to the spatial extent than in the surface layer, but they show a tendency toward prolonged durations and stronger severities. The product differences in the magnitude and severity of the drought events are consistent with the differences in soil moisture trends, which demonstrates that the representation of soil moisture trends plays a fundamental role in the drought-detection capacity of the different products.

Characterizing Pathogen-Induced Changes in Black Walnut Volatile Organic Compounds Following Inoculation with Geosmithia Morbida, The Causal Agent of Thousand Cankers Disease.

Thousand cankers disease (TCD) is a pathosystem comprised of Juglandacea spp., a pathogenic fungus Geosmithia morbida, and an insect vector, the walnut twig beetle (WTB) (Pityophthorus juglandis). Of the North American Juglans species, Juglans nigra is the most susceptible to TCD and has resulted in significant decline and mortality of urban and plantation trees in the western United States. Geosmithia morbida causes necrotic cankers in the phloem, and infected trees may release an array of volatile compounds that act as important chemical cues to WTB. Here, we aimed to determine how J. nigra volatile profiles respond to G. morbida infection as these changes can offer valuable insights into plant defense mechanisms and potentially influence WTB behavior, thus impacting disease transmission dynamics. In this study, we collected a series of bark and leaf volatiles from J. nigra seedlings inoculated with one of three isolates of G. morbida and a sham-inoculated control. Our results suggest J. nigra bark responds to G. morbida infection, with the western United States isolate (RN-2) eliciting a distinct volatile response compared to other treatments. We identified six out of fourteen compounds that contribute to 80% of the dissimilarity between RN-2 and sham-inoculated control trees. Inoculation with isolate RN-2 elicited the largest change in volatile profiles and resulted in the smallest cankers in the phloem, suggesting these compounds my play important defensive roles in J. nigra against the fungal pathogen that causes TCD.

Streamflow and Groundwater Response to Stream Restoration Using Beaver Dam Analogues in a Semi‐Arid Perennial Stream

ABSTRACTDegradation of stream and riparian environments across the western United States has damaged critical ecosystems, water quality, and increased sedimentation of reservoirs. Low tech, process‐based restoration methods such as beaver dam analogues (BDAs) have been adopted by practitioners because they restore ecosystem function, improve habitat, and reduce downstream sediment delivery at a low cost. However, few studies have examined the potential impacts of beaver dam analogues on the quantity and timing of streamflow, which is of primary concern for water stakeholders. We address this gap with 2 years of streamflow and riparian groundwater observations before and after installing a series of 17 BDAs on Fish Creek, a first‐order stream in semi‐arid northern Utah. Within 8 weeks of BDA installation, and 1 year later, we found no significant change in streamflow compared with control and Regional Reference sites. Shallow groundwater table elevations within 7 m of the stream edge increased significantly, up to 14 cm, relative to the control reach. Our results suggest that the small, local hydrological changes from BDA installation are superimposed on much larger‐scale snowmelt and alluvial groundwater controls on streamflow, suggesting BDA installation can restore ecosystem function without deleterious impacts on streamflow. These findings are especially relevant to restoration and water stakeholders with concerns about impacts of BDAs on downstream flows.

Sources and Trends of CO, O3, and Aerosols at the Mount Bachelor Observatory (2004–2022)

Understanding baseline O3 is important as it defines the fraction of O3 coming from global sources and not subject to local control. We report the occurrence and sources of high baseline ozone days, defined as a day where the daily maximum 8 h average (MDA8) exceeds 70 ppb, as observed at the Mount Bachelor Observatory (MBO, 2.8 km asl) in Central Oregon from 2004 to 2022. We used various indicators and enhancement ratios to categorize each high-O3 day: carbon monoxide (CO), aerosol scattering, the water vapor mixing ratio (WV), the aerosol scattering-to-CO ratio, backward trajectories, and the NOAA Hazard Mapping System Fire and Smoke maps. Using these, we identified four causes of high-O3 days at the MBO: Upper Troposphere/Lower Stratosphere intrusions (UTLS), Asian long-range transport (ALRT), a mixed UTLS/ALRT category, and events enhanced by wildfire emissions. Wildfire sources were further divided into two categories: smoke transported in the boundary layer to the MBO and smoke transported in the free troposphere from more distant fires. Over the 19-year period, 167 high-ozone days were identified, with an increasing fraction due to contributions from wildfire emissions and a decreasing fraction of ALRT events. We further evaluated trends in the O3 and CO data distributions by season. For O3, we found an overall increase in the mean and median values of 2.2 and 1.5 ppb, respectively, from the earliest part of the record (2004–2013) compared to the later part (2014–2022), but no significant linear trends in any season. For CO, we found a significant positive trend in the summer 95th percentiles, associated with increasing fires in the Western U.S., and a strong negative trend in the springtime values at all percentiles (1.6% yr−1 for 50th percentile). This decline was likely associated with decreasing emissions from East Asia. Overall, our findings are consistent with the positive trend in wildfires in the Western United States and the efforts in Asia to decrease emissions. This work demonstrates the changing influence of these two source categories on global background O3 and CO.

Complexities in post-wildfire governance: lessons from Colorado’s 2020 wildfires

BackgroundThe increasing size and severity of western U.S. wildfires in recent years has generated greater attention towards post-wildfire response and recovery. Post-fire governance requires coordinating response and recovery capacities across jurisdictions, landscapes, and time scales. The presence of wildfire on federal public lands necessitates federal agency involvement in both suppression and recovery efforts, and program coordination with lower levels of government and non-governmental organizations. Using semi-structured interviews, we investigated experiences of leaders across the governance system with federal post-fire policies and programs following the record-breaking Cameron Peak and East Troublesome wildfires in the state of Colorado.ResultsOur research found that persistent administrative and coordination challenges exist within and among federal agencies in the post-fire response and recovery space. Challenges included cross-jurisdictional coordination of key emergency response programs, program rules that affect post-fire project timing and effectiveness, the absence of a formal federal post-fire response strategy, and program funding issues. These factors revealed and exacerbated scale mismatches between existing agency capacities and the post-fire landscapes that result from unprecedentedly longer, larger, and more severe wildfires occurring in the western USA. Non-federal and non-governmental organizations were instrumental in overcoming these challenges through coordinating response and recovery efforts across both federal and private lands. To improve the federal post-fire response capacity, study participants stressed the importance of broader cross-jurisdictional use of federal resources, longer timeframes for recovery activities, and reforming the federal funding process.ConclusionsOur findings revealed a persistence of post-fire coordination and funding issues within federal land management agencies, and current agency capacities remain insensitive to the scale of twenty-first-century post-wildfire settings. Addressing the mismatches between existing agency resources and the spatial and temporal scale complexities of post-fire environments will require broader federal support for existing programs along with re-envisioning the overall approach to the post-fire response and recovery process.

Revisiting the Relationship between Weather and Interannual Variation in Human Plague Cases in the Southwestern United States.

Plague is a rare, potentially fatal flea-borne zoonosis endemic in the western United States. A previous model described interannual variation in human cases based on temperature and lagged precipitation. We recreated this model in northeastern Arizona (1960-1997) to evaluate its capacity to predict recent cases (1998-2022). In recreating the original model, we found that future instead of concurrent temperature had inadvertently been used for the presented fit. Prediction from our revised models with lagged precipitation and temporally plausible temperature relationships aligned with low observed cases in 1998-2022. Elevated precipitation associated with high cases in historical data (>6 inches combined precipitation over two previous springs) was only observed once in the last quarter century, so we could not assess if these conditions were reliably associated with elevated (four or more) human plague cases. Observed weather conditions were similar to those previously associated with low (fewer than or equal to two) case counts, suggesting "baseline" conditions in the last quarter century.

Data-Driven Decision Support to Guide Sustainable Grazing Management

Data-driven decision support can help guide sustainable grazing management by providing an accurate estimate of grazing capacity, in coproduction with managers. Here, we described the development of a decision support model to estimate grazing capacity and illustrated its application on two sites in the western United States. For the Montgomery Pass Wild Horse Territory in California and Nevada, the upper limit estimated in the capacity assessment was 398 horses and the current population was 654 horses. For the Eagle Creek watershed of the Apache–Sitgreaves National Forest of eastern Arizona, the lower end of capacity was estimated at 1560 cattle annually, compared to the current average of 1090 cattle annually. In addition to being spatio-temporally comprehensive, the model provides a repeatable, cost-effective, and transparent process for establishing and adjusting capacity estimates and associated grazing plans that are supported by scientific information, in order to support livestock numbers at levels that are sustainable over time, including levels that are below average forage production during drought conditions. This modeling process acts as a decision support tool because it enables different assumptions to be used and explored to accommodate multiple viewpoints during the planning process.

Lomatium Species of the Intermountain Western United States: A Chemotaxonomic Investigation Based on Essential Oil Compositions.

Lomatium is a genus of 98 species, widely distributed in western North America. This work presents a chemometric analysis of the essential oils of seven species of Lomatium (L. anomalum, L. dissectum var. dissectum, L. multifidum, L. nudicaule, L. packardiae, L. papilioniferum, and L. triternatum var. triternatum) from the intermountain western United States (Oregon and Idaho). The essential oils were obtained by hydrodistillation and analyzed by gas chromatographic methods. Lomatium packardiae essential oil can be characterized as limonene-rich, L. anomalum is a species rich in sabinene and α-pinene, and L. multifidum essential oils were rich in myrcene, while L. dissectum var. dissectum essential oils were dominated by octyl acetate and decyl acetate, L. papilioniferum essential oils from western Idaho had high p-cymene and 2-methyl-5-(1,2,2-trimethylcyclopentyl)phenol concentrations, while those from Oregon had relatively high β-phellandrene and sedanenolide levels. The essential oils of L. triternatum var. triternatum were too variable to confidently assign a chemical type. The major components in the L. nudicaule essential oils were β-phellandrene (16.0-45.7%), (Z)-ligustilide (5.6-47.1%), (E)-β-ocimene (3.3-9.9%), and δ-3-carene (0.2-12.6%). The enantiomeric distributions of α-pinene, camphene, sabinene, β-pinene, limonene, and linalool were also utilized to discriminate between the Lomatium taxa. There are not enough consistent data to properly characterize L. triternatum var. triternatum or the Oregon L. papilioniferum essential oils. Additional research is needed to confidently describe the chemotype(s) of these species.

Evaluating continental channel-hosted Lockeia orientation as a paleoflow indicator: insights from the Jurassic Brushy Basin Member, Western United States

Although bivalves can orient infaunal body position to current direction, trace fossils of bivalves have rarely been corroborated against paleocurrent directions determined from physical sedimentary structures. This study compares Lockeia (bivalve-generated trace fossil) orientation and length to the three-dimensional bedform cross-strata dip direction from fluvial deposits at two localities in the Late Jurassic Brushy Basin Member (Morrison Formation) of the western United States. Lockeia mean orientation at each site are comparable, but tangential, to physical sedimentary structure mean orientations. Comparing accuracy (within one standard deviation) and precision (within two standard deviations) in-context of five macroform surfaces, the Lockeia measurements are more accurate indicators of current direction than the physical sedimentary structures. Conversely, the physical sedimentary structures are more precise than the Lockeia measurements. This dissimilarity is partly a function of the variability of cross-stratum dip orientation produced by three-dimensional bedforms resultant from the tangential nature of the bedform, its preservation, and the method by which these are measured. Lockeia has greater paleocurrent representation accuracy than physical sedimentary structures since it is a linear measurement rather than a collection of measurements that can be tangential to paleoflow. Lockeia measurements show shifts vertically and laterally with macroform changes indicating potential use for identifying local changes in paleocurrent direction.

Substantially underestimated global health risks of current ozone pollution

Existing assessments might have underappreciated ozone-related health impacts worldwide. Here our study assesses current global ozone pollution using the high-resolution (0.05°) estimation from a geo-ensemble learning model, with key focuses on population exposure and all-cause mortality burden. Our model demonstrates strong performance, achieving a mean bias of less than -1.5 parts per billion against in-situ measurements. We estimate that 66.2% of the global population is exposed to excess ozone for short term (> 30 days per year), and 94.2% suffers from long-term exposure. Furthermore, severe ozone exposure levels are observed in Cropland areas, particularly over Asia. Importantly, the all-cause ozone-attributable deaths significantly surpass previous recognition from specific diseases worldwide. Notably, mid-latitude Asia (30°N) and the western United States show high mortality burden, contributing substantially to global ozone-attributable deaths. Our study highlights current significant global ozone-related health risks and may benefit the ozone-exposed population in the future.

Molecular shifts in dissolved organic matter along a burn severity continuum for common land cover types in the Pacific Northwest, USA.

Increasing wildfire severity is of growing concern in the western United States, with consequences for the production, composition, and mobilization of dissolved organic matter (DOM) from terrestrial to aquatic systems. Our current understanding of wildfire impacted DOM (often termed pyrogenic DOM) composition is largely built from temperature-based studies that can be difficult to extrapolate to field conditions, which are often defined by 'burn severity', or the post-wildfire impact observed at a site. Thus, burn severity can encapsulate a broader range of fire and environmental conditions not exclusive to temperature. Biogeochemical studies that describe DOM along burn severity continuums remain limited but are needed to better link DOM composition with field conditions post-fire. In this study, we addressed this need with an experimental open air burn simulation that generated chars from vegetation representative of major land cover types in the western United States. The chars were leached to simulate DOM mobilization potential. The DOM composition was characterized by ultra-high resolution mass spectrometry (HR-MS) and UV/VIS absorbance and fluorescence. Our results indicated that the shifts of DOM production and composition along a burn-severity gradient depends on the land cover type that was burned, with the degree of change dependent on the composition of the starting parent vegetation material. Fluorescence signatures indicated a strong convergence across land cover types to more aromatic DOM with increasing severity, while HR-MS indicated an increase in the production of aromatic nitrogen containing DOM with increasing severity. Results from this study enhance our ability to describe DOM composition in a framework that can be more directly related with field and remote-sensing based metrics.

Spatio-temporal analysis of extreme air pollution and risk assessment.

Extreme air pollution poses global health and environmental threats, necessitating robust policy interventions. This study first analyses the surface mass concentration of major aerosols (such as black carbon, organic carbon, dust, sea salts, and sulphates) to estimate global PM2.5 concentrations from 1980 to 2023. The developed model-estimated PM2.5 database was validated against data from 526 cities worldwide, showing strong accuracy, with RMSE, r, and R2 values of 7.47μg/m³, 0.87, and 0.75, respectively. The motivation arises from the need to understand whether recent pollution increases are driven by rising emissions or natural variability, given the significant impacts on life and property. To assess both short-and long-term pollution trends, magnitudes, and risks, we proposed twelve novel extreme pollution indices, which comprehensively characterize the spatial and temporal variations in pollution. The highest PM2.5 concentrations were observed in regions near the Saharan Desert, reaching up to 90,000μg/m³. However, significant PM2.5TOT (total pollution) concentrations were also found in the Indo-Gangetic Plain (IGP) and eastern China, ranging from 20,000 to 40,000μg/m³. Persistent pollution burdens North Africa for approximately 350 days annually, while the IGP and eastern China experience extreme pollution for over 200 days yearly. Other pollution indices highlight the intensity and frequency of pollution in regions such as North Africa, IGP, Eastern Russia, Western USA, and Eastern China, revealing critical regional air quality challenges. Our analysis identifies cities in low-income and middle-income countries, such as New Delhi, Lahore, Dhaka, and Dammam, as being at extreme risk scores above 90 out of 100. Meanwhile, cities like Ghaziabad, Chongqing, Kolkata, Mumbai, and East London fall into the high-risk category, scoring between 60 and 80. Conversely, most cities in the EU, USA, and Canada are at very low risk, a result of the effective implementation of strategic air pollution norms and policies. The study promotes a phased approach for low- and middle-income regions, emphasizing achievable air quality standards, low-cost monitoring, targeted interventions, urban greening, public awareness, and innovative financing for improvements.

Voxel Volumes and Biomass: Estimating Vegetation Volume and Litter Accumulation of Exotic Annual Grasses Using Automated Ultra-High-Resolution SfM and Advanced Classification Techniques.

In much of the northern Great Basin of the western United States, rangelands, and semi-arid ecosystems invaded by exotic annual grasses such as cheatgrass (Bromus tectorum) and medusahead (Taeniatherum caput-medusae) are experiencing an increasingly short fire cycle, which is compounding and persistent. Improving and expanding ground-based field methods for measuring the above-ground biomass (AGB) may enable more sample collections across a landscape and over succession regimes and better harmonize with other remote sensing techniques. Developments and increased adoption of unoccupied aerial systems (UAS) and instrumentation for vegetation monitoring enable greater understanding of vegetation in many ecosystems. Research to understand the relationship of traditional field measurements with remotely sensed data in rangeland environments is growing rapidly, and there is increasing interest in the use of aerial platforms to quantify AGB and fine-fuel load at pasture and landscape scales. Our study uses relatively inexpensive handheld photography with custom quadrat sampling frames to collect and automatically reconstruct 3D models of the vegetation within 0.2 m2 quadrats (n = 288). Next, we examine the relationship between volumetric estimates of vegetation with biomass. We found that volumes calculated with 0.5 cm voxel sizes (0.125 cm3) most closely represented the range of biomass weights. We further develop methods to classify ground points, finding a 2% reduction in predictive ability compared with validation ground surface reconstructions. This finding is significant given that our study site is characterized by a dense litter layer covering the ground surface, making reconstruction challenging. Overall, our best reconstruction workflow had an R2 of 0.42, further emphasizing the importance of high-resolution imagery and reconstruction techniques. Ultimately, we conclude that more work is needed of increasing extents (such as from UAS) to better understand and constrain uncertainties in volumetric estimations of biomass in ecosystems with high amounts of invasive annual grasses and fine-fuel litter.

Urban morphology and urban water demand: a case study in the land constrained Los Angeles region using urban growth modeling

Abstract The interactions between population growth, urban morphology, and water demand have important implications for water resources and supply in urban regions. Water use for irrigation comprises a significant fraction of urban water demand, and is potentially influenced by long-term changes in urban morphology. To investigate this, we used spatially explicit projections of urban land development intensity (fraction impervious area) generated from a 30 m resolution urban growth model for the Los Angeles (LA) region. Recent historical data on water use and high resolution landcover were used to establish relationships between green area, urban development intensity, and outdoor water demand. These relationships were then used to project outdoor and total water demand in 2100 using the urban growth model outputs. We considered two different population scenarios informed by the shared socioeconomic pathway (SSP) projections for the region (SSP3 and SSP5), and three scenarios of urban development intensification. Our analysis is resolved for over 80 water providers in the region, from the urban core to suburban fringe, and highlights diverse demand responses influenced by initial urban form and water demand attributes. Assumptions about outdoor water use factors based on recent water supply data were found to be nearly as influential on future outdoor demand as the urban growth scenario settings. Compared to previous studies, our work is unique in coherently linking high resolution SSP population scenarios, urban land cover evolution, and urban water demand projections, demonstrating the approach for the LA region—the largest population center in the western United States.

Climate matching models for Ceratapion basicorne (Coleoptera: Apionidae), a biocontrol agent of yellow starthistle

Abstract Ceratapion basicorne (Illiger) (Coleoptera: Apionidae), a weevil native to Europe and western Asia, shows promise for enhancing the control of yellow starthistle (Centaurea solstitialis L.), an invasive annual forb in the western United States. However, a paucity of data on this biocontrol agent’s environmental constraints has made it difficult to assess the suitability of potential release locations. Climate matching models were developed for C. basicorne to help identify areas of the western United States with similar climates to the source area of breeding colonies being used for releases (home location). The models used climate variables derived from daily estimates of minimum temperature, maximum temperature, precipitation, and soil moisture for a 30-yr period spanning 1991–2020 at 1 km2 resolution. Of the areas where C. solstitialis is known to occur, the Central California Foothills, Eastern Cascades Foothills, Columbia Plateau, and mountainous parts of northcentral Utah had the most similar climates to the home location. Of these areas, the Eastern Cascades foothills in northeastern California and Wasatch Range in Utah occurred at a similar latitude as the home location, which may be important to consider if C. basicorne has photoperiodic diapause. The least similar climates occurred in wet coastal regions, high-elevation (cold) mountains, and hot deserts; however, C. solstitialis has not been detected in most of these areas. The development of process-based models for predicting the establishment of this agent will require a more detailed understanding of the agent’s requirements for development and survival.

Comparisons of Montane Snow Water Equivalent Projections: Calculating Total Snow Mass in Regions with Projection Agreement and Divergence in the Western US

Abstract Montane snowpack is a vital source of water in the Western United States. Here, we use a large-ensemble approach to evaluate the agreement across 124 snow water equivalent (SWE) projections with statistically downscaled forcing between end-of-century (2076 – 2095) and early 21st century (2106 – 2035) periods. Comparisons were performed on dates corresponding with the end of winter (15 April) and mid-spring snowmelt (15 May) in five western US domains. Using 1) the percent change to end-of-century SWE across different ensembles of snow projections, and 2) the shift between early 21st century and end-of-century SWE distributions for each snow projection, we identified relationships between projections that were consistent across each domain. In low to mid-elevations, end-of-century SWE decreases were 48% and larger on 15 April. These regions had projected changes to SWE that were both high-confidence and in relative agreement across projections. Despite this, the majority of 15 April SWE volume existed in higher elevations where the magnitude and direction (positive or negative) of SWE changes were most uncertain. The results of this study show that large-ensemble approaches can be used to measure coherence between snow projections and identify 1) the highest-confidence changes to future snow water resources, and 2) the locations and periods where and when improvements to snow projections would most benefit estimates of future snow water resources.

Terrestrial evidence for volcanogenic sulfate-driven cooling event ~30 kyr before the Cretaceous-Paleogene mass extinction.

Alongside the Chicxulub meteorite impact, Deccan volcanism is considered a primary trigger for the Cretaceous-Paleogene (K-Pg) mass extinction. Models suggest that volcanic outgassing of carbon and sulfur-potent environmental stressors-drove global temperature change, but the relative timing, duration, and magnitude of such change remains uncertain. Here, we use the organic paleothermometer MBT'5me and the carbon-isotope composition of two K-Pg-spanning lignites from the western Unites States, to test models of volcanogenic air temperature change in the ~100 kyr before the mass extinction. Our records show long-term warming of ~3°C, probably driven by Deccan CO2 emissions, and reveal a transient (<10 kyr) ~5°C cooling event, coinciding with the peak of the Poladpur "pulse" of Deccan eruption ~30 kyr before the K-Pg boundary. This cooling was likely caused by the aerosolization of volcanogenic sulfur. Temperatures returned to pre-event values before the mass extinction, suggesting that, from the terrestrial perspective, volcanogenic climate change was not the primary cause of K-Pg extinction.

Anthropogenically protected but naturally disturbed: a specialist carnivore at its southern range periphery

AbstractUnderstanding how species distributions and associated habitat are impacted by natural and anthropogenic disturbance is central for the conservation of rare forest carnivores dependent on subalpine forests. Canada lynx at their range periphery occupy subalpine forests that are structured by large-scale fire and insect outbreaks that increase with climate change. In addition, the Southern Rocky Mountains of the western United States is a destination for winter recreationists worldwide with an associated high degree of urbanization and resort development. We modeled habitat for a reintroduced population of Canada lynx in the Southern Rocky Mountains using an ensemble species distribution model built on abiotic and biotic covariates and validated with independent lynx locations including satellite telemetry, aerial telemetry, camera traps, den locations, and winter backtracking. Based on this model, we delineated Likely and Core lynx-habitat as thresholds that captured 95% and 50% of testing data, respectively. Likely (5727 km2) and Core (441 km2) habitat were spatially limited and patchily distributed across western Colorado, USA. Natural (e.g., insect outbreaks, fire) and anthropogenic (e.g., urbanization, ski resort development, forest management) disturbance overlapped 37% of Likely lynx-habitat and 24 % of highest quality Core. Although overlap with fire disturbance was low (5%), future burns likely represent the greatest potential impact over decades-long timeframes. The overlap of publicly owned lands administratively classified as “protected” with Likely (62% overlap) and Core (49%) habitat may insulate lynx from permanent habitat conversion due to direct human disturbance (urbanization, ski resort development).