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USGS2021

Projected change in rangeland fractional component cover across the sagebrush biome under climate change through 2085

Climate change over the past century has altered vegetation community composition and species distributions across rangelands in the western United States. The scale and magnitude of climatic influences are unknown. While many studies have projected the effects of climate change using several modeling approaches, none has evaluated the impacts to fractional component cover at a 30-m resolution across the full sagebrush ( Artemisia spp.) biome. We used fractional component cover data for rangeland functional groups and weather data from the 1985 to 2018 reference period in conjunction with soils and topography data to develop empirical models describing the spatiotemporal variation in component cover. To investigate the ramifications of future change across the western United States, we extended models based on historical relationships over the reference period to model landscape effects based on future weather conditions from two emission scenarios and three time periods (2020s, 2050s, and 2080s). We tested both generalized additive models (GAMs) and regression tree models, finding that the former led to superior spatial and statistical results. Our results indicate more xeric vegetation across most of the study area, with an increasing dominance of non-sagebrush shrubs, annual herbaceous cover, and bare ground over herbaceous and sagebrush cover in both the representative concentration pathway (RCP) 4.5 and 8.5 scenarios. In general, both scenarios yielded similar results, but RCP 8.5 tended to be more extreme, with greater change relative to the reference period. Results demonstrate that in cool sites some degree of warming to growing season maximum temperature or nongrowing season minimum temperature could be beneficial to sagebrush and shrub growth. However, warming nongrowing season maximum temperature was beneficial to shrub, but not to sagebrush growth. Our results inform rangeland managers of potential future vegetation composition, cover, and species distributions, which could improve prioritization of conservation and restoration efforts.

Arizona, California, Colorado, Idaho, Montana, Nev↗

USGS2026

Timing is everything: Drivers of upstream movement of fishes

Objective Understanding whether fishes quickly respond to shifting temperatures and flows, especially as they pass through river reaches that may be thermally unsuitable, may help to prioritize climate-informed management strategies. Methods Here, we use 15 years of daily fish passage data (2005–2020) from the Leaburg Dam on the McKenzie River, Oregon, USA, with water temperatures and river flows from two associated gauges. We examine the relative influence of temperature, flow, and calendar date on fish moving upstream, the range of conditions experienced by each species, and long-term patterns in timing, supported by annual count data from the years 1971–2020. Results Comparisons of timing and conditions while each species passed upstream through the Leaburg Dam fish ladders revealed that some taxa were more consistent seasonally (e.g., Pacific Lamprey Entosphenus tridentatus and Largescale Sucker Catostomus macrocheilus ), experiencing a more restricted range of conditions, while others moved throughout the year under highly variable environmental conditions (e.g., trout). For both groups, calendar date appeared to be a primary driver of movement timing, even when local environmental factors of temperature and flow were considered. We note broad trends toward earlier passage across all species except Chinook Salmon Oncorhynchus tshawytscha . Notable declines in movement of Mountain Whitefish Prosopium williamsoni and Largescale Suckers occurred during years of extreme weather events, indicating that they may be particularly sensitive to the combined impacts of water temperature and flow and could serve as sentinel taxa. Conclusions Although timing is recognized as a driver for the onset of migrations, this suggests that most fish may continue to move upriver during consistent time periods, potentially increasing their risk of exposure to suboptimal environmental conditions. Our results demonstrate the utility of long-term passage data for detecting patterns in local timing, environmental conditions co-occurring with fish movement, and the sensitivity of different fish species in responding to environmental extremes during upstream migrations.

Oregon↗

USGS2010

Climate warming-induced intensification of the hydrologic cycle: A review of the published record and assessment of the potential impacts on agriculture

Climate warming is expected to intensify and accelerate the global hydrologic cycle resulting in increases in evaporation, evapotranspiration (ET), atmospheric water-vapor content, and precipitation. The strength of the hydrologic response, or sensitivity of the response for a given degree of warming, is a critical outstanding question in climatology and hydrology. In this review chapter, I examine the published record of trends in various components of the hydrologic cycle and associated variables to assess observed hydrologic responses to warming during the period of observational records. Global and regional trends in evaporation, ET, and atmospheric water-vapor content and several large river basin water-balance studies support an ongoing intensification of the hydrologic cycle. Global trends in precipitation, runoff, and soil moisture are more uncertain than the trends in the variables noted above, in part because of high spatial and temporal variability. Trends in associated variables, such as systematic changes in ocean salinity, the length of the growing season, and the rate of precipitation recycling are generally consistent with intensification of the hydrologic cycle. The evidence for an increase in the frequency, intensity, or duration of extreme-weather events like hurricanes is mixed and remains uncertain. The largest potential impacts to agricultural systems depend greatly on the responses of hydrologic variables that are the most uncertain; for example, intensity and duration of heavy rainfall events; frequency, intensity, and duration of major storms and droughts; and rates of erosion. Impacts on agriculture will depend greatly on how insects, diseases, weeds, nutrient cycling, effectiveness of agrichemicals, and heat stress are affected by an intensification of the hydrologic cycle.

Advances in Agronomy↗

USGS2021

Can we advance individual-level heat-health research through the application of stochastic weather generators?

Individuals living in every region of the world are increasingly vulnerable to negative health outcomes due to extreme heat exposure. Children, in particular, may face long-term consequences associated with heat stress that affect their educational attainment and later life health and well-being. Retrospective individual-level analyses are useful for determining the effects of extreme heat exposure on health outcomes. Typically, future risk is inferred by extrapolating these effects using future warming scenarios that are applied uniformly over space and time without consideration of topographical or climatological gradients. We propose an alternative approach using a stochastic weather generator. This approach employs a 1 °C warming scenario to produce an ensemble of plausible future weather scenarios, and subsequently a distribution of future health risks. We focus on the effect of global warming on fetal development as measured by birth weight in Ethiopia. We demonstrate that predicted changes in birth weight are sensitive to the evolution of temperatures not quantified in a uniform warming scenario. Distributions of predicted changes in birth weight vary in magnitude and variability depending on geographic and socioeconomic region. We present these distributions alongside results from the uniform warming scenario and discuss the spatiotemporal variability of these predicted changes.

Climatic Change↗

USGS2007

Climate variation at Flagstaff, Arizona - 1950 to 2007

Much scientific research demonstrates the existence of recent climate variation, particularly global warming. Climate prediction models forecast that climate will change; it will become warmer, droughts will increase in number and severity, and extreme climate events will recur often—desiccating aridity, extremely wet, unusually warm, or even frigid at times. However, the global models apply to average conditions in large grids approximately 150 miles on an edge (Thorpe, 2005), and how or whether specific areas within a grid are affected is unclear. Flagstaff's climate is mentioned in the context of global change, but information is lacking on the amount and trend of changes in precipitation, snowfall, and temperature. The purpose of this report is to understand what may be happening to Flagstaff's climate by reviewing local climate history. Flagstaff is in north-central Arizona south of San Francisco Mountain, which reaches 12,633 feet, the highest in Arizona (fig. 1). At 6,900 feet, surrounded by ponderosa pine forest, Flagstaff enjoys a four-season climate; winter-daytime temperatures are cool, averaging 45 degrees (Fahrenheit). Summer-daytime temperatures are comfortable, averaging 80 degrees, which is pleasant compared with nearby low-elevation deserts. Flagstaff's precipitation averages 22-inches per year with a range of 9 to 39 inches. Snowfall occurs each season, averaging 97 inches annually. This report, written for the non-technical reader, interprets climate variation at Flagstaff as observed at the National Weather Service (NWS) station at Pulliam Field (or Airport), a first-order weather station staffed by meteorologists (Staudenmaier and others, 2007). The station is on a flat-topped ridge surrounded by forest 5-miles south of Flagstaff at an elevation of 7,003 feet. Data used in this analysis are daily measurements of precipitation (including snowfall) and temperature (maximum and minimum) covering the period from 1950, when the station began operation, through spring 2007. Conversations with Byron Peterson and Michael Staudenmaier of the NWS helped us understand the difficulties of collecting consistent weather data, operation of the station, and Flagstaff's climate. Weather is the daily or even instantaneous state of temperature and precipitation. Climate is the average or accumulation of these parameters over longer time scales such as a week, month, or year. Seasonal (winter, spring, summer, and fall) and annual averages of temperature and accumulated precipitation describe the temporal variation of Flagstaff's climate, which is shown graphically with time series (figs. 2, 4, 6, 8-15). These plots show precipitation or temperature on the ordinate plotted against time on the abscissa, which is a year for annually repeating data or the year of a particular season. The plots reveal changing patterns of precipitation and temperature related to droughts, wet episodes, and rising temperatures.

Arizona↗

USGS1993

Relict colluvial boulder deposits as paleoclimatic indicators in the Yucca Mountain region, southern Nevada

Early to middle Pleistocene boulder deposits are common features on southern Nevada hillslopes. These darkly varnished, ancient colluvial deposits stand but in stark contrast to the underlying light-colored bedrock of volcanic tuffs, and they serve as minor divides between drainage channels on modern hillslopes. To demonstrate the antiquity of these stable hillslope features, six colluvial boulder deposits from Yucca Mountain, Nye County, Nevada, were dated by cation- ratio dating of rock varnish accreted on boulder surfaces. Estimated minimum ages of these boulder deposits range from 760 to 170 ka. Five additional older deposits on nearby Skull and Little Skull Mountains and Buckboard Mesa yielded cation-ratio minimum-age estimates of 1.38 Ma to 800 ka. An independent cosmogenic chlorine-36 surface exposure date was obtained on one deposit, which confirms an estimated early to middle Quaternary age. These deposits have provided the oldest age estimates for unconsolidated hillslope deposits in the southwestern United States. We suggest that the colluvial boulder deposits were produced during early and middle Pleistocene glacial/pluvial episodes and were stabilized during the transition to drier interglacial climates. By comparison to modern periglacial environments, winter minimum monthly temperatures of -3 to -5 °C were necessary to initiate freeze-thaw conditions of such vigor to physically weather relatively large volumes of large boulders from the upper hillslopes of the Yucca Mountain area. These conditions imply that early and middle Pleistocene glacial winter temperatures were at least 1 to 3 °C colder than existed during the last Pleistocene glacial episode and 7 to 9 °C colder than present. We conclude that at least several early and middle Pleistocene glacial episodes were colder, and perhaps wetter, than glacial episodes of the late Pleistocene in the southern Great Basin. Geomorphic processes necessary to form these colluvial boulder deposits are not active on modern hillslopes in the southern Great Basin. In addition, the lack of young, relatively unvarnished colluvial boulder deposits on these hillslopes suggests that boulder-forming conditions did not exist during the late Pleistocene in this region. Modern semiarid hillslope processes primarily erode colluvium during infrequent high-intensity storms. The preservation of old, thin hillslope deposits and the less-than-2-m incision by hillslope runoff adjacent to these deposits, however, indicate that extremely low denudation rates have occurred on resistant volcanic hillslopes in the southern Great Basin during Quaternary time.

Nevada↗

USGS2026

Mississippi’s resiliency and changing environmental conditions

Mississippi is experiencing shifts in environmental conditions, many of which are expected to intensify in the coming decades, and will have important implications for ecosystems, species, and natural resource management across the state. Historical climate analyses and downscaled projections summarized for the state’s Environmental Protection Agency (EPA) level III Ecoregions show that Mississippi will likely face increases in extremely hot days, more intense heatwaves, greater evapotranspiration, and reductions in cold-season extremes. Temperature trends indicate that while Mississippi has warmed relatively little over the last century, recent years have been among the warmest on record. Projections suggest substantial increases in the number of days with maximum temperatures at or above 95°F across all Ecoregions, particularly under higher warming scenarios. Correspondingly, the number of freezing nights is expected to decline, with statewide decreases of 7–21 days depending on the global warming level and timeframe. These combined patterns are likely to reshape habitat conditions, influence species’ thermal stress, and alter ecological processes such as soil moisture retention and stream temperature regimes. Mississippi’s hydrological systems are also expected to be significantly affected. Extreme rainfall events, particularly the most intense 1% of precipitation days, are projected to increase across the state, raising risks of flooding, erosion, and altered stream flow. Coastal Mississippi faces additional stress from sea‑level rise, which is already contributing to more frequent high‑tide flooding; projections show continued increases in inundation risk throughout the century. These flooding patterns, combined with stronger hurricane rainfall rates and the potential for landfalling storms to stall, pose ongoing threats to coastal ecosystems and communities. The state is also vulnerable to extreme weather hazards such as tornadoes. Recent research shows a geographic shift in tornado activity toward the Southeast, with Mississippi experiencing some of the nation’s greatest increases in favorable tornado days and nighttime tornado frequency—hazards that have direct implications for wildlife, habitat stability, and human safety. Drought conditions may intensify as well: higher temperatures and increased evapotranspiration during dry spells could worsen water stress regardless of uncertainty in average annual precipitation. These changing environmental conditions have important consequences for Mississippi’s Species of Greatest Conservation Need (SGCN). Vulnerability assessments and ecological niche models indicate that several fish, mussel, crayfish, plant, amphibian, bird, and mammal species may face heightened stress due to warming temperatures, shifting hydrology, habitat loss, and increases in extreme events. For example, many cold‑water and moisture‑dependent species in the state’s rivers and wetlands are already near their thermal limits, and further warming could reduce suitable habitat. Birds breeding in bottomland hardwood forests, such as the Prothonotary Warbler, are increasingly susceptible to nest loss from flooding. Similarly, species like the Louisiana Black Bear may encounter higher risks from habitat inundation and shifting food availability. The “A Closer Look” section underscores the vulnerability of the Mississippi Alluvial Plain—one of the state’s most ecologically rich yet heavily altered Ecoregions. Its bottomland hardwood forests, wetlands, and floodplain habitats support diverse wildlife but are increasingly threatened by rising temperatures, hydrological changes, development pressures, and compounded disturbances. These habitats provide critical ecosystem services such as water filtration, flood attenuation, and biodiversity support, making their conservation particularly urgent under future conditions. Collectively, these findings indicate that Mississippi’s ongoing and projected environmental changes present both challenges and opportunities for natural resource management. Incorporating adaptation strategies into the State Wildlife Action Plan will be essential for sustaining habitats, mitigating risks, and supporting the long‑term resilience of Mississippi’s wildlife and ecosystems.

Mississippi↗

USGS2026

The contribution of a surge event to infilling in a barrier-enclosed estuary: Insights from field observations

Many estuaries worldwide face increasing sediment loading caused by catchment land use change and intensification, creating subsequent adverse effects on estuarine ecosystems. Extreme weather events can disproportionately alter sediment pathways and loading. Although storm-driven sediment exchange has been widely examined at open coasts and inlets, key transport mechanisms within constricted, sheltered estuaries remain understudied. This study presents an observational dataset capturing the impact of a 99th percentile water-level event (based on 20 years of records) on sediment transport pathways in a sheltered, barrier-enclosed estuary. This event, driven by a 3-day storm surge (>0.5 m) combined with a spring tide, was recorded during a 3-week field campaign. Sediment transport pathways and riverine contributions were analysed, and observations revealed substantial changes in suspended sediment concentrations increasing from 18 mg/l to 70 mg/l during the event. The elevated water levels and resulting pressure gradient at the constricted study site entrance caused by the storm surge increased local flood dominance. Combined with higher flow velocities and resuspension, the storm led to a sixfold increase in sediment import at the estuary entrance and a 600-fold increase in sediment flux to the upper estuary. The decoupling of peak suspended sediment concentrations from streamflow indicates that the resuspension of estuarine legacy sediment, rather than catchment inputs, dominated the system's response. These findings challenge assumptions about estuarine sediment budgets and emphasise that incorporating high water-level surge events into models can enhance the prediction of long-term estuarine evolution. Given projected increases in storm frequency under climate change, understanding these episodic but highly consequential sediment pulses can support the assessment of wetland resilience and inform estuarine management strategies.

Whangateau Estuary↗

USGS2024

Canopy cover and microtopography control precipitation-enhanced thaw of ecosystem-protected permafrost

Northern high-latitudes are projected to get warmer and wetter, which will affect rates of permafrost thaw and mechanisms by which thaw occurs. To better understand the impact of rain, as well as other factors such as snow depth, canopy cover, and microtopography, we instrumented a degrading permafrost plateau in south-central Alaska with high-resolution soil temperature sensors. The site contains ecosystem-protected permafrost, which persists in unfavorable climates due to favorable ecologic conditions. Our study (2020–2022) captured three of the snowiest years and three of the four wettest years since the site was first studied in 2015. Average thaw rates along an across-site transect increased nine-fold from 6 ± 5 cm yr −1 (2015–2020) to 56 ± 12 cm yr −1 (2020–2022). This thaw was not uniform. Hummock locations, residing on topographic high points with relatively dense canopy, experienced only 8 ± 9 cm yr −1 of thaw, on average. Hollows, topographic low points with low canopy cover, and transition locations, which had canopy cover and elevation between hummocks and hollows, thawed 44 ± 6 cm yr −1 and 39 ± 13 cm yr −1 , respectively. Mechanisms of thaw differed between these locations. Hollows had high warm-season soil moisture, which increased thermal conductivity, and deep cold-season snow coverage, which insulated soil. Transition locations thawed primarily due to thermal energy transported through subsurface taliks during individual rain events. Most increases in depth to permafrost occurred below the ∼45 cm thickness seasonally frozen layer, and therefore, expanded existing site taliks. Results highlight the importance of canopy cover and microtopography in controlling soil thermal inputs, the ability of subsurface runoff from individual rain events to trigger warming and thaw, and the acceleration of thaw caused by consecutive wet and snowy years. As northern high-latitudes become warmer and wetter, and weather events become more extreme, the importance of these controls on soil warming and thaw is likely to increase.

Alaska↗

USGS2025

Chapter 6: Climate change, wildlife, and wildlife habitats in the Oregon Coast Range

Climate change is likely to have profound effects on wildlife species within the Oregon Coast Adaptation Partnership (OCAP) assessment area, although the direction and magnitude of effects are likely to vary across species. Increased mean and extreme temperatures, especially during summer, may cause shifts in plant and animal species ranges, reduce habitat for some temperature-sensitive wildlife, alter plant phenology and the timing of available food resources, and affect species interactions (e.g., predation, competition). Altered timing of precipitation, summer drought, loss of fog, increased flooding events, earlier snowmelt, and rising sea level may reduce plant productivity, increase tree mortality, shift plant species composition, and lead to reduced wildlife habitat and habitat quality for some forests, riparian areas, wetlands, meadows, estuaries, and beaches. In addition, increasing frequency and extent of wildfire and insect outbreaks may reduce the extent of late-successional forest, reduce habitat connectivity, and increase the spread of invasive species. The biggest change expected for the assessment area is an increase in area where climatic conditions favor coastal mixed forest and a large reduction in area favoring montane conifer forest. Although actual changes in forest types may not necessarily occur by the end of the 21st century, climate change may add physiological and behavioral stress to wildlife. Some wildlife species will be able to persist in place and adapt to new conditions; some may be able to migrate to find suitable habitat; and some may be greatly reduced or extirpated from the assessment area or even go extinct. Shifts in major tree and shrub species will play a major role in food, den, and cover availability for wildlife. Rising sea level will reduce low-elevation habitats along the coast. An increase in the frequency of high-severity weather events will increase frequency and magnitude of flooding, including debris flow events. Coupled with increased temperatures during summer, this may reduce or fragment important ecosystems for aquatic and semi-aquatic species. Evaluation of the vulnerabilities of nine wildlife species based on literature reviews suggests that each species has life-history attributes that can lead to resilience or vulnerability to climate change effects. Depending on long-term objectives, several broad adaptation strategies focus on protecting refugia, establishing redundant wildlife strongholds with large-scale connectivity, and promoting structural and biological complexity.

Oregon↗

USGS2021

The triple argon isotope composition of groundwater on ten-thousand-year timescales

Understanding the age and movement of groundwater is important for predicting the vulnerability of wells to contamination, constraining flow models that inform sustainable groundwater management, and interpreting geochemical signals that reflect past climate. Due to both the ubiquity of groundwater with order ten-thousand-year residence times and its importance for climate reconstruction of the last glacial period, there is a strong need for improving geochemical dating tools on this timescale. Whereas 14 C of dissolved inorganic carbon and dissolved 4 He are common age tracers for Late Pleistocene groundwater, each is limited by systematic uncertainties related to aquifer composition and lithology, and the extent of water-rock interaction. In principle, radiogenic 40 Ar in groundwater acquired from decay of 40 K in aquifer minerals should be insensitive to some processes that impact 14 C and 4 He and thus represent a useful, complementary age tracer. In practice, however, detection of significant radiogenic 40 Ar signals in groundwater has been limited to a small number of studies of extremely old groundwater (>100 ka). Here we present the first high-precision (<1‰) measurements of triple Ar isotopes ( 40 Ar, 38 Ar, 36 Ar) in groundwater. We introduce a model that distinguishes radiogenic 40 Ar from atmospheric 40 Ar by using the non-radiogenic Ar isotopes ( 36 Ar, 38 Ar) to correct for mass-dependent fractionation. Using this model, we investigate variability in radiogenic 40 Ar excess (Δ 40 Ar) across 58 groundwater samples collected from 36 wells throughout California (USA). We find that Δ 40 Ar ranges from ~0‰ (the expected minimum value) to +4.2‰ across three study areas near Fresno, San Diego, and the western Mojave Desert. Based on measurements from a network of 23 scientific monitoring wells in San Diego, we find evidence for a strong dependence of Δ 40 Ar on aquifer lithology. We suggest that Δ 40 Ar is fundamentally controlled by the weathering of old K-bearing minerals and thus reflects both the degree of groundwater-rock interaction, which is related to groundwater age, and the integrated flow through different geological formations. Future studies of Late Pleistocene groundwater may benefit from high-precision triple Ar isotope measurements as a new tool to better interpret 14 C- and 4 He-based constraints on groundwater age and flow.

Chemical Geology↗

USGS2005

Assessing climate change effects on mountain ecosystems using integrated models: A case study

Mountain systems are characterized by strong environmental gradients, rugged topography and extreme spatial heterogeneity in ecosystem structure and composition. Consequently, most mountainous areas have relatively high rates of endemism and biodiversity, and function as species refugia in many areas of the world. Mountains have long been recognized as critical entities in regional climatic and hydrological dynamics but their importance as terrestrial carbon stores has only been recently underscored (Schimel et al. 2002; this volume). Mountain ecosystems, therefore, are globally important as well as unusually complex. These ecosystems challenge our ability to understand their dynamics and predict their response to climatic variability and global-scale environmental change. To meet this challenge, mountain scientists increasingly are modeling the vast array of relationships that comprise ecosystem dynamics. Dynamic modeling can examine the interactions between land management strategies and climatic change to develop appropriate responses to future human demands on mountain systems. Modeling provides spatially and temporally explicit, quantified results that can be validated in the field, thus providing feedback to our understanding of ecosystem dynamics. Modeling results, particularly maps and other visual tools, also give a concrete dimension to our understanding of the scale and magnitude of potential future changes. Modeling alerts scientists and land managers to apparently counter-intuitive outcomes of ecosystem responses to climate change or management decisions. For instance, in an early modeling exercise for northwest Montana, USA, Running and Nemani (1991) found that streamflow in a warmer future climate decreased by 30% in the Swan Range even when precipitation was increased by 10% in a particular climate change scenario. This unexpected response was due to enhanced forest growth, and increased evapotranspiration, resulting from the earlier snowmelt and extended growing season. There is a rich legacy of models that address climate and weather, hydrology, forest growth (e.g. gap dynamics and succession), forest fires (e.g. fuel loading) and land cover change (cf. Bugmann et al., this volume). Much less common, however, are attempts to fully integrate models from various disciplines to create a robust system that adequately addresses the entire range of ecosystem dynamics. In addition, fine-resolution modeling of entire mountain ranges (i.e. regional ecosystem scale) is not as common as global or continental scale modeling or watershed/catchment scale modeling. However, this is the scale that is germane to policy decisions such as in the western US and Canada, i.e. in those areas that contain most of the mountainous terrain of North America. This paper describes our efforts to implement an integrated regional modeling approach while characterizing potential future responses of a mountain ecosystem to climate change. Our study area was Glacier National Park in northwestern Montana, USA. Glacier Park is a 4082 km” mountain wilderness that straddles the continental divide and contains over 150 summits of up to 3150 m elevation in the Lewis and Livingston mountain ranges.

Book chapter↗

USGS2009

Assessment of fire behavior and management options in subalpine vegetation on Mauna Kea, Hawai'i

Fire is a major threat to habitat for the endangered Palila (Loxioides bailleui) within subalpine vegetation on Mauna Kea volcano, Hawai‘i. The presence of large amounts of fine fuel from grasses, dry climate, and human ignition sources produces a significant risk of wildfire in this area year-round. The purpose of this report is to provide information on fuels and potential fire behavior that will contribute to fire management of Palila habitat. Recommended actions will contribute to the conservation of these native forests and facilitate restoration in degraded areas. To assess the effects of grass invasion on fuel conditions and potential fire danger, we quantified vegetation and fuels across an elevation gradient from grasslands into sub-alpine forests on the west slope of Mauna Kea. Our results indicated that grass cover was reduced under tree canopy in plots below ~2,500 m elevation, but at higher elevations grass cover was higher under trees than in the open. However, tree canopy cover below 2,500 m elevation was not high enough overall (~25% on average) to result in significant reductions in fine fuels at the landscape level. Sampling directly under and away from tree crowns at multiple elevations suggested that below ~2,500 m, the presence of tree canopy cover can reduce grass fuels significantly. Furthermore, moisture content of live surface fuels was increased under tree canopy compared with open areas. These results suggest that restoration of forest cover may have the potential to alter grass fuels in ways that decrease the threat of fire in some subalpine forests. Fire behavior estimates based on fuel data from grasslands, mixed forest and māmane forest indicated the need for fuelbreaks of at least 20-30 m to limit fire spread in most areas. In many cases, breaks as wide as 40 m are required to limit fire spread risk under extreme weather conditions. Based on our fuels data and fire behavior predictions, recommended actions include: (1) construction of new or expansion of existing fuelbreaks to immediately reduce fire risk to the most sensitive areas adjacent to the core Palila population on the southwest slope and the translocated Palila population on the north slope of Mauna Kea, (2) enhancement of forest restoration activities to increase fuel moisture and reduce grass fuel loads (3) installation of water sources (diptanks) in both areas to decrease firefighter response time, and (4) increased public education and awareness with regard to fire danger on Mauna Kea.

Hawaii↗

USGS2026

Changing drivers of regional large magnitude avalanche frequency throughout Colorado, USA

Large magnitude snow avalanches (destructive size ≥ D3) impact settlements, transportation corridors, and public safety worldwide. In Colorado, United States, avalanches have killed more people than any other natural hazard since 1950. In March 2019, a large magnitude avalanche cycle occurred throughout the entire mountainous portion of Colorado resulting in more than 1000 reported avalanches during a two-week period. Nearly 200 of these avalanches were size D4 or larger with at least three D5 avalanches. However, placing this 2019 large magnitude avalanche cycle in historic context requires data prior to the instrumental record. Here, we paired tree disturbance data from dendrochronology (1698 to 2020) with meteorological data from the modeled and instrumental record (1901 to 2020) to understand the frequency and climate drivers of large magnitude snow avalanche cycles. The extensive number of downed trees from the 2019 avalanche cycle allowed us to collect 1,188 cross-sections and cores from 1023 individual trees within 24 avalanche paths across the state. From these samples we identified 4135 avalanche-related growth disturbances. We employed a strategic nested sampling design to spatially aggregate avalanche frequency from individual avalanche paths, to counties, to three major sub-regions (i.e., north, central, and south), and across the entire region (i.e., state of Colorado). Over a period spanning more than three centuries (1698 to 2020), we identified 76 avalanche years within 24 individual avalanche paths. Large magnitude avalanche event frequency varied across paths and sub-regions with several notable region-wide avalanche cycles. Both tree-ring and historical written records highlighted 1899 as a year with widespread and large magnitude avalanche activity similar to the March 2019 avalanche cycle. Since the early-20th century (1900 to 2020) regional avalanche probability declined significantly in parallel with decreasing snowpack throughout Colorado. Similarly, dominant avalanche regimes shifted from large magnitude regional cycles driven by above average snowfall years over most of the record, to regional avalanche cycles occurring more commonly in average to low snow years since 1988. In recent decades, a lack of December precipitation and above average March precipitation characterized years with regional large magnitude avalanche activity. Even with declining snow water equivalent, truly extreme regional large magnitude avalanche cycles remain possible – as demonstrated by the 2019 cycle. This underscores that rare but high-impact events are not eliminated by long-term trends. Understanding the changing snow and weather drivers and subsequent behavior of large magnitude avalanche cycles across multiple spatial scales may improve avalanche forecasting and the products and mitigations strategies developed by structural engineers to mitigate avalanche danger. This can decrease the avalanche risk to the public and improve infrastructure design in avalanche terrain.

Colorado↗

USGS2025

A nationwide evaluation of crowd-sourced ambient temperature data

Growing concerns about heat in urban areas paired with the sparsity of weather stations have resulted in individuals drawing on data from citizen science sensor networks to fill in data gaps. The PurpleAir are the most widely-used low-cost air quality sensors in the contiguous United States with 14,777 deployed between 1 Jan 2017 and 20 July 2021. Although the air quality data from PurpleAir sensors have been widely studied, less attention has been paid to reported temperature. We compare temperature metrics reported by PurpleAir sensors with a gridded temperature product, the North American Land Data Assimilation System (NLDAS)-2, which although not a gold-standard measure of temperature, is widely used in epidemiologic research. We evaluate the lag between indoor and outdoor PurpleAir temperatures. We report associations of the difference between outdoor PurpleAir temperatures and NLDAS-2 temperatures, an indicator of degradation, and the duration of sensor operation. Finally, based on the temperature range recorded by the outdoor PurpleAir sensors vis.a.vis NLDAS-2 temperatures, we provide a list of 271 (2.5%) sensors potentially misclassified as outdoor and likely located indoors. We observed that outdoor PurpleAir sensors agreed well with NLDAS-2 (R2 > 0.82). This association broke down under warm conditions (daily average NLDAS ≥ 21.1oC). Landcover and climate zone were significant modifiers of the association between PurpleAir and NLDAS-2 temperature metrics with the poorest PurpleAir- NLDAS-2 agreement in urban areas. Indoor PurpleAir temperatures lagged hourly NLDAS temperatures by two hours across almost all climate zones. The mean difference in hourly PurpleAir and NLDAS-2 temperatures increased by 0.57oC for every operational year, suggesting that careful attention must be paid to degradation. Overall, we find for use in epidemiological studies, that the PurpleAir sensor data is a reliable metric of daytime mean air temperature, but researchers should be aware of its limitations when examining extreme heat, or when aggregating sensor data across multiple years.

Frontiers of Environmental Science and Engineering↗

USGS2024

Forest fire, thinning, and flood in wildland-urban interface: UAV and lidar-based estimate of natural disaster impacts

Context Wildland-urban interface (WUI) areas are facing increased forest fire risks and extreme precipitation events due to climate change, which can lead to post-fire flood events. The city of Flagstaff in northern Arizona, USA experienced WUI forest thinning, fire, and record rainfall events, which collectively contributed to large floods and damages to the urban neighborhoods and city infrastructure. Objectives We demonstrate multi-temporal, high resolution image applications from an unoccupied aerial vehicle (UAV) and terrestrial lidar in estimating landscape disturbance impacts within the WUI. Changes in forest vegetation and bare ground cover in WUIs are particularly challenging to estimate with coarse-resolution satellite images due to fine-scale landscape processes and changes that often result in mixed pixels. Methods Using Sentinel-2 satellite images, we document forest fire impacts and burn severity. Using 2016 and 2021 UAV multispectral images and Structure-from-Motion data, we estimate post-thinning changes in forest canopy cover, patch sizes, canopy height distribution, and bare ground cover. Using repeat lidar data within a smaller area of the watershed, we quantify geomorphic effects in the WUI associated with the fire and subsequent flooding. Results We document that thinning significantly reduced forest canopy cover, patch size, tree density, and mean canopy height resulting in substantially reduced active crown fire risks in the future. However, the thinning equipment ignited a forest fire, which burned the WUI at varying severity at the top of the watershed that drains into the city. Moderate-high severity burns occurred within 3 km of downtown Flagstaff threatening the WUI neighborhoods and the city. The upstream burned area then experienced 100-year and 200–500-year rainfall events, which resulted in large runoff-driven floods and sedimentation in the city. Conclusion We demonstrate that UAV high resolution images and photogrammetry combined with terrestrial lidar data provide detailed and accurate estimates of forest thinning and post-fire flood impacts, which could not be estimated from coarser-resolution satellite images. Communities around the world may need to prepare their WUIs for catastrophic fires and increase capacity to manage sediment-laden stormwater since both fires and extreme weather events are projected to increase.

Arizona↗

USGS2002

Evaluation of factors affecting ice forces at selected bridges in South Dakota

During 1998-2002, the U.S. Geological Survey, in cooperation with the South Dakota Department of Transportation (SDDOT), conducted a study to evaluate factors affecting ice forces at selected bridges in South Dakota. The focus of this ice-force evaluation was on maximum ice thickness and ice-crushing strength, which are the most important variables in the SDDOT bridge-design equations for ice forces in South Dakota. Six sites, the James River at Huron, the James River near Scotland, the White River near Oacoma/Presho, the Grand River at Little Eagle, the Oahe Reservoir near Mobridge, and the Lake Francis Case at the Platte-Winner Bridge, were selected for collection of ice-thickness and ice-crushing-strength data. Ice thickness was measured at the six sites from February 1999 until April 2001. This period is representative of the climate extremes of record in South Dakota because it included both one of the warmest and one of the coldest winters on record. The 2000 and 2001 winters were the 8th warmest and 11th coldest winters, respectively, on record at Sioux Falls, South Dakota, which was used to represent the climate at all bridges in South Dakota. Ice thickness measured at the James River sites at Huron and Scotland during 1999-2001 ranged from 0.7 to 2.3 feet and 0 to 1.7 feet, respectively, and ice thickness measured at the White River near Oacoma/Presho site during 2000-01 ranged from 0.1 to 1.5 feet. At the Grand River at Little Eagle site, ice thickness was measured at 1.2 feet in 1999, ranged from 0.5 to 1.2 feet in 2000, and ranged from 0.2 to 1.4 feet in 2001. Ice thickness measured at the Oahe Reservoir near Mobridge site ranged from 1.7 to 1.8 feet in 1999, 0.9 to 1.2 feet in 2000, and 0 to 2.2 feet in 2001. At the Lake Francis Case at the Platte-Winner Bridge site, ice thickness ranged from 1.2 to 1.8 feet in 2001. Historical ice-thickness data measured by the U.S. Geological Survey (USGS) at eight selected streamflow-gaging stations in South Dakota were compiled for 1970-97. The gaging stations included the Grand River at Little Eagle, the White River near Oacoma, the James River near Scotland, the James River near Yankton, the Vermillion River near Wakonda, the Vermillion River near Vermillion, the Big Sioux River near Brookings, and the Big Sioux River near Dell Rapids. Three ice-thickness-estimation equations that potentially could be used for bridge design in South Dakota were selected and included the Accumulative Freezing Degree Day (AFDD), Incremental Accumulative Freezing Degree Day (IAFDD), and Simplified Energy Budget (SEB) equations. These three equations were evaluated by comparing study-collected and historical ice-thickness measurements to equation-estimated ice thicknesses. Input data required by the equations either were collected or compiled for the study or were obtained from the National Weather Service (NWS). An analysis of the data indicated that the AFDD equation best estimated ice thickness in South Dakota using available data sources with an average variation about the measured value of about 0.4 foot. Maximum potential ice thickness was estimated using the AFDD equation at 19 NWS stations located throughout South Dakota. The 1979 winter (the coldest winter on record at Sioux Falls) was the winter used to estimate the maximum potential ice thickness. The estimated maximum potential ice thicknesses generally are largest in northeastern South Dakota at about 3 feet and are smallest in southwestern and south-central South Dakota at about 2 feet. From 1999 to 2001, ice-crushing strength was measured at the same six sites where ice thickness was measured. Ice-crushing-strength measurements were done both in the middle of the winter and near spring breakup. The maximum ice-crushing strengths were measured in the mid- to late winter before the spring thaw. Measured ice-crushing strengths were much smaller near spring breakup. Ice-crushing strength measured at the six sites

Water-Resources Investigations Report↗

USGS2021

Characterization of historical and stochastically generated climate and streamflow conditions in the Souris River Basin, United States and Canada

The Souris River Basin is a 61,000-square-kilometer basin in the Provinces of Saskatchewan and Manitoba in Canada and the State of North Dakota in the United States. Greater than average snowpack during the winter of 2010–11, along with record-setting rains in May and June 2011, resulted in historically unprecedented flooding in the Souris River Basin. The severity of the 2011 flood led the United States and Canada to request a review of the operating plan for any improvements of reservoir operations and flood control measures in the basin, and the Souris River Basin Task Force was formed. The International Souris River Study Board was then formed in 2017 to carry out the recommendations of the Souris River Basin Task Force laid out in a plan of study. To support the International Souris River Study Board, the U.S. Geological Survey (USGS), in cooperation with the North Dakota State Water Commission and the International Joint Commission, used the previously developed unregulated and regulated streamflow models and data for stochastic streamflow in the Souris River Basin to characterize climate and streamflow and support selection of streamflow traces based on their characterization. Components of the original stochastic hydrology models and their outputs were used in this phase of the study to (1) characterize historical and stochastic climate and streamflow for the Souris River Basin, (2) disaggregate monthly stochastic streamflow spatially and temporally to meet the needs of the U.S. Army Corps of Engineers, Hydrologic Engineering Center, Reservoir System Simulation model for the Souris River Basin, and (3) discuss selection of disaggregated streamflow traces (simulations) using the characteristics of climate and streamflow. A trace is a time series of a stochastic variable such as streamflow, potential evapotranspiration, or precipitation. To characterize climate conditions, precipitation, potential evapotranspiration (PET), and moisture deficit for the Souris River Basin and individual points at Rafferty, Grant Devine, and Lake Darling Reservoirs were determined annually and seasonally. The annual basin (November 1–October 31) precipitation for the 50-percent nonexceedance probability is 452 millimeters (mm). Spring (March–May) is the wettest season, followed by summer (June–August), fall (September–November), and winter (December–February). Annual moisture deficit was largest at Lake Darling Reservoir, followed by Rafferty Reservoir, and then Grant Devine Reservoir. Annual maximum monthly mean streamflow was determined for the Souris River below Rafferty Reservoir, Saskatchewan (Canadian streamgage 05NB036); Long Creek near Noonan (above Boundary Reservoir), North Dakota (USGS streamgage 05113600); Moose Mountain Creek near Oxbow, Saskatchewan (Canadian streamgage 05ND004); the Souris River near Sherwood, N. Dak. (USGS streamgage 05114000); the Des Lacs River at Foxholm, N. Dak. (USGS streamgage 05116500); and the Souris River above Minot, N. Dak. (USGS streamgage 05117500). When the seasonal maximum monthly mean streamflows are evaluated in contrast to annual maximum monthly mean streamflows separated by their seasonal occurrence, summer months of annual maximum monthly mean streamflows have a higher 50-percent exceedance probability of streamflow compared to annual maximum monthly mean streamflows that occur in spring, seasonal maximum monthly mean streamflows that occur in spring, and seasonal maximum monthly mean streamflows that occur in summer. When annual maximum monthly mean streamflows in summer are compared to annual maximum monthly mean streamflows in spring, they are consistently higher in streamflow but occur in less than 4.2 percent of years. Evaluation of whether the annual maximum monthly mean streamflows that occur in summer can be described as a separate population from annual maximum monthly mean streamflows that occur in spring was outside the scope of this study, and the summer and spring annual maximum monthly mean streamflows were not tested for statistical differences in mean or variance. Further investigation of seasonal weather patterns that induce flooding could lead to a better understanding of the seasonal differences in flooding. Long-term hydrologic drought was characterized by evaluating multiyear mean streamflow. Shorter averaging periods have greater streamflow variability than longer periods and hence have a wider range of values. As the averaging period is extended to a longer period, the variability of mean streamflow decreases, and the more extreme streamflow volumes seen in shorter averaging periods cannot be sustained. Stochastic streamflow time series were disaggregated spatially and temporally for use in a HEC–ResSim model. The combination of monthly and daily stochastic streamflow data was used to select traces with qualities that could be used to test alternatives focused on water supply, summer flooding, and apportionment.

Manitoba, North Dakota, Saskatchewan↗