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USGS2018

Responses of unimpaired flows, storage, and managed flows to scenarios of climate change in the San Francisco Bay-Delta watershed

Projections of meteorology downscaled from global climate model runs were used to drive a model of unimpaired hydrology of the Sacramento/San Joaquin watershed, which in turn drove models of operational responses and managed flows. Twenty daily climate change scenarios for water years 1980–2099 were evaluated with the goal of producing inflow boundary conditions for a watershed sediment model and for a hydrodynamical model of the San Francisco Bay-Delta estuary. The resulting time series of meteorology, snowpack, unimpaired flow, reservoir storage, and managed flow were analyzed for century-scale trends. In the Sacramento basin, which dominates Bay-Delta inflows, all 20 scenarios portrayed warming trends (with a mean of 4.1 °C) and most had precipitation increases (with a mean increase of 9%). Sacramento basin snowpack water equivalent declined sharply (by 89%), which was associated with a major shift toward earlier unimpaired runoff timing (33% more flow arriving prior to 1 April). Sacramento basin reservoirs showed large declines in end-of-September storage. Water-year averaged outflows increased for most scenarios for both unimpaired and impaired flows, and frequency of extremely high daily unimpaired and impaired flows increased (increases of 175% and 170%, respectively). Managed Delta inflows were projected to experience large increases in the wet season and declines in the dry season. Changes in management strategy and infrastructure can mitigate some of these changes, though to what degree is uncertain.

California↗

USGS2018

Past and future global transformation of terrestrial ecosystems under climate change

Impacts of global climate change on terrestrial ecosystems are imperfectly constrained by ecosystem models and direct observations. Pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was comparable in magnitude to warming projected for the next century under high-emission scenarios. We reviewed 594 published paleoecological records to examine compositional and structural changes in terrestrial vegetation since the last glacial period and to project the magnitudes of ecosystem transformations under alternative future emission scenarios. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change and suggest that, without major reductions in greenhouse gas emissions to the atmosphere, terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

Science↗

USGS2022

Response in the water level of Anvil Lake, Wisconsin, to changes in meteorological and climatic changes, Wisconsin

Anvil Lake, a relatively shallow seepage lake in northern Wisconsin, USA, has experienced dramatic changes in water level since elevation records began in 1938 in response to changes in meteorological and climatic conditions (Figure 1. Robertson et al., 2018). Anvil Lake’s water level record shows a pronounced 10–15-yr cycle, with recurring highs and lows with a typical swing of over 1 m. Although experiencing large cycles in water levels, the long-term average levels were relatively stable until about 1987, when water level dropped dramatically by an additional 1 m (in 2016). Water levels then rebounded dramatically, reaching near “normal” water levels in 2020. At its lowest level, the lake had a maximum depth of 8.2 m (mean depth of 4.7 m) and an area of 128 ha. Like most long-term records, Anvil Lake’s water level record has been measured by several observers using various techniques. To verify the consistency of the various datums used throughout this period, historical photographs with the water’s edge identified were obtained, tied to NAVD 1988 using a Real Time Kinematic satellite global positioning system, and compared with the measured water levels (See Figure 1). To determine the causes of the changes in water level, a complete water budget was estimated for Anvil Lake from 1980 to 2014. Water levels in Anvil Lake were simulated (Figure 1) using a hydrodynamic model (General Lake Model, GLM), with daily lake evaporation estimated by GLM, monthly lake/groundwater exchange estimated with a groundwater model (MODFLOW), daily precipitation from the North American Land Data Assimilation System (NLDAS), and stream inflow and outflow were set as zero because the lake has no inlets or outlet. Atmospheric fluxes (precipitation minus evaporation) primarily drove the lake-level fluctuations and trends, but sub-decadal fluctuations in net groundwater exchange (groundwater inflow minus lake seepage) either enhanced or reduced the lake level response to the atmospheric drivers. The changes in water levels were shown to affect the extent of stratification and water quality in the lake (Robertson et al., 2018). During periods of lower precipitation and lower water levels, Anvil Lake was a polymictic lake, whereas during periods of higher precipitation and higher water levels the lake was a dimictic lake with stratification lasting throughout summer. During periods with higher water levels, the water quality in the lake was shown to improve slightly as a result of the nutrients being diluted in a larger volume of water. If precipitation increases in the future, as results from many General Circulation Models (GCMs) suggest (Robertson et al., 2016), and if that outweighs the effects of increased evaporation caused by increased air temperatures, water levels in Anvil Lake may be expected to fluctuate at a higher level. Higher water levels in Anvil Lake are expected to result in the lake becoming more strongly stratified and have slightly improved water quality (lower nutrient and algal concentrations and increased water clarity) (Robertson et al., 2018).

Wisconsin↗

USGS2020

Non-freezing cold event stresses can cause significant damage to mangrove seedlings: Assessing the role of warming and nitrogen enrichment in a mesocosm study

Mangroves are expanding poleward along coastlines globally as a response to rising temperatures and reduced incidence of freezing under climate change. Yet, knowledge of mangrove responses to infrequent cold events in the context of future global and regional environmental changes is limited. We initiated a mesocosm experiment in which the seedlings of two mangrove species were grown either at ambient temperature or under warming with and without nitrogen (N) loading. During a short winter period, an unusually severe cold event occurred with the lowest temperature of 2°C. We assessed the possible response of these two mangrove species to the cold stress. We found that the cold event caused various degrees of damage to the seedlings of both mangrove species, with the warming treatment seemingly protecting leaves and branches from the cold damage. However, warming did not buffer mangroves to mortality from those low temperatures in either species. The cold event resulted in a significant decrease in seedling growth rates and net ecosystem CO2 uptake in the post-cold period relative to the pre-cold period, though the cold event did not alter the effects of warming on these parameters of both mangrove species. The cold event differentially altered physiological responses of the two species growing under N loading, with A. marina growing in higher N concentrations having a reduced growth response after the cold event, whereas B. gymnorrhiza displayed no change in post-cold period versus pre-cold period growth. Our findings suggest the pivotal role of cold events, versus freeze events, in regulating mangrove survival and growth even under future warming scenarios. Two mangrove species exhibited differential survival and growth responses to the cold event at different N concentrations, which has implications for how we can restore and conserve mangroves among the world's eutrophied sub-tropical estuaries and with future warming.

Environmental Research↗

USGS2010

Response of lake chemistry to changes in atmospheric deposition and climate in three high-elevation wilderness areas of Colorado

Trends in precipitation chemistry and hydrologic and climatic data were examined as drivers of long-term changes in the chemical composition of high-elevation lakes in three wilderness areas in Colorado during 1985–2008. Sulfate concentrations in precipitation decreased at a rate of −0.15 to −0.55 μeq/l/year at 10 high-elevation National Atmospheric Deposition Program stations in the state during 1987–2008 reflecting regional reductions in SO 2 emissions. In lakes where sulfate is primarily derived from atmospheric inputs, sulfate concentrations also decreased although the rates generally were less, ranging from −0.12 to −0.27 μeq/l/year. The similarity in timing and sulfur isotopic data support the hypothesis that decreases in atmospheric deposition are driving the response of high-elevation lakes in some areas of the state. By contrast, in lakes where sulfate is derived primarily from watershed weathering sources, sulfate concentrations showed sharp increases during 1985–2008. Analysis of long-term climate records indicates that annual air temperatures have increased between 0.45 and 0.93°C per decade throughout most mountainous areas of Colorado, suggesting climate as a factor. Isotopic data reveal that sulfate in these lakes is largely derived from pyrite, which may indicate climate warming is preferentially affecting the rate of pyrite weathering.

Colorado↗

USGS2020

What are the effects of climate variability and change on ungulate life-histories, population dynamics, and migration in western North America? A systematic map protocol

Climate is an important driver of ungulate life-histories, population dynamics, and migratory behaviors, and can affect the growth, development, fecundity, dispersal, and demographic trends of populations. Changes in temperature and precipitation, and resulting shifts in plant phenology, winter severity, drought and wildfire conditions, invasive species distribution and abundance, predation, and disease have the potential to directly or indirectly affect ungulates. However, ungulate responses to climate variability and change are not uniform and vary by species and geography. Here, we present a systematic map protocol aiming to describe the abundance and distribution of evidence on the effects of climate variability and change on ungulate life-histories, population dynamics, and migration in North America. This map will help to identify knowledge gaps and clusters of evidence, and can be used to inform future research directions and adaptive management strategies.

Environmental Evidence↗

USGS2011

Vulnerability of riparian ecosystems to elevated CO 2 and climate change in arid and semiarid western North America

Riparian ecosystems, already greatly altered by water management, land development, and biological invasion, are being further altered by increasing atmospheric CO 2 concentrations ([CO 2 ]) and climate change, particularly in arid and semiarid (dryland) regions. In this literature review, we (1) summarize expected changes in [CO 2 ], climate, hydrology, and water management in dryland western North America, (2) consider likely effects of those changes on riparian ecosystems, and (3) identify critical knowledge gaps. Temperatures in the region are rising and droughts are becoming more frequent and intense. Warmer temperatures in turn are altering river hydrology: advancing the timing of spring snow melt floods, altering flood magnitudes, and reducing summer and base flows. Direct effects of increased [CO 2 ] and climate change on riparian ecosystems may be similar to effects in uplands, including increased heat and water stress, altered phenology and species geographic distributions, and disrupted trophic and symbiotic interactions. Indirect effects due to climate-driven changes in streamflow, however, may exacerbate the direct effects of warming and increase the relative importance of moisture and fluvial disturbance as drivers of riparian ecosystem response to global change. Together, climate change and climate-driven changes in streamflow are likely to reduce abundance of dominant, native, early-successional tree species, favor herbaceous species and both drought-tolerant and late-successional woody species (including many introduced species), reduce habitat quality for many riparian animals, and slow litter decomposition and nutrient cycling. Climate-driven changes in human water demand and associated water management may intensify these effects. On some regulated rivers, however, reservoir releases could be managed to protect riparian ecosystem. Immediate research priorities include determining riparian species' environmental requirements and monitoring riparian ecosystems to allow rapid detection and response to undesirable ecological change.

Global Change Biology↗

USGS2024

Vulnerability of mineral-associated soil organic carbon to climate across global drylands

Mineral-associated organic carbon (MAOC) constitutes a major fraction of global soil carbon and is assumed less sensitive to climate than particulate organic carbon (POC) due to protection by minerals. Despite its importance for long-term carbon storage, the response of MAOC to changing climates in drylands, which cover more than 40% of the global land area, remains unexplored. Here we assess topsoil organic carbon fractions across global drylands using a standardized field survey in 326 plots from 25 countries and 6 continents. We find that soil biogeochemistry explained the majority of variation in both MAOC and POC. Both carbon fractions decreased with increases in mean annual temperature and reductions in precipitation, with MAOC responding similarly to POC. Therefore, our results suggest that ongoing climate warming and aridification may result in unforeseen carbon losses across global drylands, and that the protective role of minerals may not dampen these effects.

Nature Climate Change↗

USGS2011

Shifting species interactions in terrestrial dryland ecosystems under altered water availability and climate change

Species interactions play key roles in linking the responses of populations, communities, and ecosystems to environmental change. For instance, species interactions are an important determinant of the complexity of changes in trophic biomass with variation in resources. Water resources are a major driver of terrestrial ecology and climate change is expected to greatly alter the distribution of this critical resource. While previous studies have documented strong effects of global environmental change on species interactions in general, responses can vary from region to region. Dryland ecosystems occupy more than one-third of the Earth's land mass, are greatly affected by changes in water availability, and are predicted to be hotspots of climate change. Thus, it is imperative to understand the effects of environmental change on these globally significant ecosystems. Here, we review studies of the responses of population-level plant-plant, plant-herbivore, and predator-prey interactions to changes in water availability in dryland environments in order to develop new hypotheses and predictions to guide future research. To help explain patterns of interaction outcomes, we developed a conceptual model that views interaction outcomes as shifting between (1) competition and facilitation (plant-plant), (2) herbivory, neutralism, or mutualism (plant-herbivore), or (3) neutralism and predation (predator-prey), as water availability crosses physiological, behavioural, or population-density thresholds. We link our conceptual model to hypothetical scenarios of current and future water availability to make testable predictions about the influence of changes in water availability on species interactions. We also examine potential implications of our conceptual model for the relative importance of top-down effects and the linearity of patterns of change in trophic biomass with changes in water availability. Finally, we highlight key research needs and some possible broader impacts of our findings. Overall, we hope to stimulate and guide future research that links changes in water availability to patterns of species interactions and the dynamics of populations and communities in dryland ecosystems.

Biological Reviews↗

USGS2013

Influences of geomorphology and geology on alpine treeline in the American West - More important than climatic influences?

The spatial distribution and pattern of alpine treeline in the American West reflect the overarching influences of geological history, lithology and structure, and geomorphic processes and landforms, and geologic and geomorphic factors—both forms and processes—can control the spatiotemporal response of the ecotone to climate change. These influences occur at spatial scales ranging from the continental scale to fine scale processes and landforms at the slope scale. Past geomorphic influences, particularly Pleistocene glaciation, have also left their impact on treeline, and treelines across the west are still adjusting to post-Pleistocene conditions within Pleistocene-created landforms. Current fine scale processes include solifluction and changes on relict solifluction and digging by animals. These processes should be examined in detail in future studies to facilitate a better understanding of where individual tree seedlings become established as a primary response of the ecotone to climate change.

The Rocky Mountains↗

USGS2016

Experience drives innovation of new migration patterns of whooping cranes in response to global change

Anthropogenic changes in climate and land use are driving changes in migration patterns of birds worldwide. Spatial changes in migration have been related to long-term temperature trends, but the intrinsic mechanisms by which migratory species adapt to environmental change remain largely unexplored. We show that, for a long-lived social species, older birds with more experience are critical for innovating new migration behaviours. Groups containing older, more experienced individuals establish new overwintering sites closer to the breeding grounds, leading to a rapid population-level shift in migration patterns. Furthermore, these new overwintering sites are in areas where changes in climate have increased temperatures and where food availability from agriculture is high, creating favourable conditions for overwintering. Our results reveal that the age structure of populations is critical for the behavioural mechanisms that allow species to adapt to global change, particularly for long-lived animals, where changes in behaviour can occur faster than evolution.

Nature Communications↗

USGS2009

Climate-induced changes in high elevation stream nitrate dynamics

Mountain terrestrial and aquatic ecosystems are responsive to external drivers of change, especially climate change and atmospheric deposition of nitrogen (N). We explored the consequences of a temperature-warming trend on stream nitrate in an alpine and subalpine watershed in the Colorado Front Range that has long been the recipient of elevated atmospheric N deposition. Mean annual stream nitrate concentrations since 2000 are higher by 50% than an earlier monitoring period of 1991-1999. Mean annual N export increased by 28% from 2.03 kg N ha -1 yr -1 before 2000 to 2.84 kg N ha -1 yr -1 in Loch Vale watershed since 2000. The substantial increase in N export comes as a surprise, since mean wet atmospheric N deposition from 1991 to 2006 (3.06 kg N ha -1 yr -1 ) did not increase. There has been a period of below average precipitation from 2000 to 2006 and a steady increase in summer and fall temperatures of 0.12??C yr -1 in both seasons since 1991. Nitrate concentrations, as well as the weathering products calcium and sulfate, were higher for the period 2000-2006 in rock glacier meltwater at the top of the watershed above the influence of alpine and subalpine vegetation and soils. We conclude the observed recent N increases in Loch Vale are the result of warmer summer and fall mean temperatures that are melting ice in glaciers and rock glaciers. This, in turn, has exposed sediments from which N produced by nitrification can be flushed. We suggest a water quality threshold may have been crossed around 2000. The phenomenon observed in Loch Vale may be indicative of N release from ice features such as rock glaciers worldwide as mountain glaciers retreat. ?? 2009 Blackwell Publishing Ltd.

Global Change Biology↗

USGS2012

Projected climate and vegetation changes and potential biotic effects for Fort Benning, Georgia; Fort Hood, Texas; and Fort Irwin, California

The responses of species and ecosystems to future climate changes will present challenges for conservation and natural resource managers attempting to maintain both species populations and essential habitat. This report describes projected future changes in climate and vegetation for three study areas surrounding the military installations of Fort Benning, Georgia, Fort Hood, Texas, and Fort Irwin, California. Projected climate changes are described for the time period 2070–2099 (30-year mean) as compared to 1961–1990 (30-year mean) for each study area using data simulated by the coupled atmosphere-ocean general circulation models CCSM3, CGCM3.1(T47), and UKMO-HadCM3, run under the B1, A1B, and A2 future greenhouse gas emissions scenarios. These climate data are used to simulate potential changes in important components of the vegetation for each study area using LPJ, a dynamic global vegetation model, and LPJ-GUESS, a dynamic vegetation model optimized for regional studies. The simulated vegetation results are compared with observed vegetation data for the study areas. Potential effects of the simulated future climate and vegetation changes for species and habitats of management concern are discussed in each study area, with a particular focus on federally listed threatened and endangered species.

Georgia;Texas;California↗

USGS2003

Modeled climate-induced glacier change in Glacier National Park, 1850-2100

The glaciers in the Blackfoot–Jackson Glacier Basin of Glacier National Park, Montana, decreased in area from 21.6 square kilometers (km 2 ) in 1850 to 7.4 km 2 in 1979. Over this same period global temperatures increased by 0.45°C (± 0.15°C). We analyzed the climatic causes and ecological consequences of glacier retreat by creating spatially explicit models of the creation and ablation of glaciers and of the response of vegetation to climate change. We determined the melt rate and spatial distribution of glaciers under two possible future climate scenarios, one based on carbon dioxide–induced global warming and the other on a linear temperature extrapolation. Under the former scenario, all glaciers in the basin will disappear by the year 2030, despite predicted increases in precipitation; under the latter, melting is slower. Using a second model, we analyzed vegetation responses to variations in soil moisture and increasing temperature in a complex alpine landscape and predicted where plant communities are likely to be located as conditions change.

Montana↗

USGS2024

Using environmental DNA to assess the response of steelhead/Rainbow Trout and Coastrange Sculpin populations to postfire debris flows in coastal streams of Big Sur, California

Objective Debris flows are among the most extreme disturbances to streams and are predicted to become more frequent under climate change. We assessed the response of steelhead Oncorhynchus mykiss (anadromous Rainbow Trout)/Rainbow Trout (hereafter, collectively referred to as O. mykiss ) and Coastrange Sculpin Cottus aleuticus populations to major postfire debris flows in two small coastal basins of California using noninvasive environmental DNA (eDNA) sampling. Methods We analyzed water samples from disturbed reaches for eDNA in the first two summers after debris flows. In Big Creek, all Coastrange Sculpin habitat was disturbed by debris flows, but a major tributary occupied by O. mykiss was not affected. In Mill Creek, all available habitat for both species was disturbed. We also sampled two unburned basins as undisturbed reference streams. Result In Big Creek, O. mykiss eDNA was detected in all water samples during both years, and concentrations in some samples approached the lowest concentrations in the reference streams. Coastrange Sculpin eDNA was detected only in a single water sample in the first year and was not detected in the second year. In Mill Creek, neither species was detected in the first year, but during the second year, O. mykiss eDNA was detected at very low concentrations in 40% of samples and Coastrange Sculpin eDNA was detected in a single sample. Conclusion Our results indicate that O. mykiss and Coastrange Sculpins either survived in or quickly reoccupied the disturbed reaches from within the basins. However, the detection rates for cases in which all habitat for a species in a basin was affected by debris flows indicate that abundances were very low, suggesting that persistence may be uncertain unless there is successful reproduction or immigration. Finally, eDNA appears to be effective for monitoring sensitive fish populations after a major disturbance; however, detection rates in individual samples may be low and require appropriate sampling designs to achieve the desired detection probability.

California↗

USGS1999

Response of high-elevation forests in the Olympic Mountains to climatic change

The gap model ZELIG was used to examine the effects of increased temperature (2°C) and altered precipitation on high-elevation ecosystems of the Olympic Mountains, Washington, U.S.A. Changes in tree species distribution and abundance, as well as stand biomass, were examined on north and south aspects in the dry northeast (NE) and wet southwest (SW) regions of the Olympics for ( i ) warmer, ( ii ) warmer and 20% wetter, and ( iii ) warmer and 20% drier climatic-change scenarios. Dominant tree species shift upwards 300-600 m in elevation in the SW, with subalpine meadows and Tsuga mertensiana (Bong.) Carr. forests being replaced by Abies amabilis (Dougl.) Forbes forests at higher elevations and A. amabilis forests being replaced by Tsuga heterophylla (Raf.) Sarg. forests at lower elevations. In the NE, drought-tolerant species become dominant approximately 200 m lower than present, with A. lasiocarpa dominating the north aspect and Pinus contorta Dougl. ex Loud. the south aspect. Biomass increases in the SW and generally decreases in the NE, depending on aspect and precipitation regime. This study suggests that species and site-specific responses at mesoscale (e.g., wet vs. dry climatic regime) and microscale (e.g., north vs. south aspect) resolutions must be characterized to quantify the variation in potential effects of climatic change on forest vegetation in mountainous regions.

Canadian Journal of Forest Research↗

USGS2009

Responses of stream nitrate and dissolved organic carbon loadings to hydrological forcing and climate change in an upland forest of the northeast USA

[1] In coming decades, higher annual temperatures, increased growing season length, and increased dormant season precipitation are expected across the northeastern United States in response to anthropogenic forcing of global climate. We synthesized long-term stream hydrochemical data from the Sleepers River Research Watershed in Vermont, United States, to explore the relationship of catchment wetness to stream nitrate and DOC loadings. We modeled changes in growing season length and precipitation patterns to simulate future climate scenarios and to assess how stream nutrient loadings respond to climate change. Model results for the 2070–2099 time period suggest that stream nutrient loadings during both the dormant and growing seasons will respond to climate change. During a warmer climate, growing season stream fluxes (runoff +20%, nitrate +57%, and DOC +58%) increase as more precipitation (+28%) and quick flow (+39%) occur during a longer growing season (+43 days). During the dormant season, stream water and nutrient loadings decrease. Net annual stream runoff (+8%) and DOC loading (+9%) increases are commensurate with the magnitude of the average increase of net annual precipitation (+7%). Net annual stream water and DOC loadings are primarily affected by increased dormant season precipitation. In contrast, decreased annual loading of stream nitrate (−2%) reflects a larger effect of growing season controls on stream nitrate and the effects of lengthened growing seasons in a warmer climate. Our findings suggest that leaching of nitrate and DOC from catchment soils will be affected by anthropogenic climate forcing, thereby affecting the timing and magnitude of annual stream loadings in the northeastern United States.

Vermont↗

USGS2015

Simulating the effect of climate change on stream temperature in the Trout Lake Watershed, Wisconsin

The potential for increases in stream temperature across many spatial and temporal scales as a result of climate change can pose a difficult challenge for environmental managers, especially when addressing thermal requirements for sensitive aquatic species. This study evaluates simulated changes to the thermal regime of three northern Wisconsin streams in response to a projected changing climate using a modeling framework and considers implications of thermal stresses to the fish community. The Stream Network Temperature Model (SNTEMP) was used in combination with a coupled groundwater and surface water flow model to assess forecasts in climate from six global circulation models and three emission scenarios. Model results suggest that annual average stream temperature will steadily increase approximately 1.1 to 3.2 °C (varying by stream) by the year 2100 with differences in magnitude between emission scenarios. Daily mean stream temperature during the months of July and August, a period when cold-water fish communities are most sensitive, showed excursions from optimal temperatures with increased frequency compared to current conditions. Projections of daily mean stream temperature, in some cases, were no longer in the range necessary to sustain a cold water fishery.

Wisconsin↗