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Geology topics

Alan L. Flint

Publications and source records attributed to Alan L. Flint.

At least 37 records · Page 2Linked to original sources
USGS2016

Characterizing changes in streamflow and sediment supply in the Sacramento River Basin, California, using hydrological simulation program—FORTRAN (HSPF)

A daily watershed model of the Sacramento River Basin of northern California was developed to simulate streamflow and suspended sediment transport to the San Francisco Bay-Delta. To compensate for sparse data, a unique combination of model inputs was developed, including meteorological variables, potential evapotranspiration, and parameters defining hydraulic geometry. A slight decreasing trend of sediment loads and concentrations was statistically significant in the lowest 50% of flows, supporting the observed historical sediment decline. Historical changes in climate, including seasonality and decline of snowpack, contribute to changes in streamflow, and are a significant component describing the mechanisms responsible for the decline in sediment. Several wet and dry hypothetical climate change scenarios with temperature changes of 1.5 °C and 4.5 °C were applied to the base historical conditions to assess the model sensitivity of streamflow and sediment to changes in climate. Of the scenarios evaluated, sediment discharge for the Sacramento River Basin increased the most with increased storm magnitude and frequency and decreased the most with increases in air temperature, regardless of changes in precipitation. The model will be used to develop projections of potential hydrologic and sediment trends to the Bay-Delta in response to potential future climate scenarios, which will help assess the hydrological and ecological health of the Bay-Delta into the next century.

California↗
USGS2016

The role of snowpack, rainfall, and reservoirs in buffering California against drought effects

California’s vast reservoir system, fed by annual snow-and rainfall, plays an important part in providing water to the State’s human and wildlife population. There are almost 1,300 reservoirs throughout the State, but only approximately 200 of them are considered storage reservoirs, and many of the larger ones are critical components of the Federal Central Valley Project and California State Water Project. Storage reservoirs, such as the ones shown in figure 1, capture winter precipitation for use in California’s dry summer months. In addition to engineered reservoir storage, California also depends on water “stored” in the statewide snowpack, which slowly melts during the course of the summer, to augment the State’s water supply.

California↗
USGS2016

Implications of projected climate change for groundwater recharge in the western United States

Existing studies on the impacts of climate change on groundwater recharge are either global or basin/location-specific. The global studies lack the specificity to inform decision making, while the local studies do little to clarify potential changes over large regions (major river basins, states, or groups of states), a scale often important in the development of water policy. An analysis of the potential impact of climate change on groundwater recharge across the western United States (west of 100° longitude) is presented synthesizing existing studies and applying current knowledge of recharge processes and amounts. Eight representative aquifers located across the region were evaluated. For each aquifer published recharge budget components were converted into four standard recharge mechanisms: diffuse, focused, irrigation, and mountain-systems recharge. Future changes in individual recharge mechanisms and total recharge were then estimated for each aquifer. Model-based studies of projected climate-change effects on recharge were available and utilized for half of the aquifers. For the remainder, forecasted changes in temperature and precipitation were logically propagated through each recharge mechanism producing qualitative estimates of direction of changes in recharge only (not magnitude). Several key patterns emerge from the analysis. First, the available estimates indicate average declines of 10–20% in total recharge across the southern aquifers, but with a wide range of uncertainty that includes no change. Second, the northern set of aquifers will likely incur little change to slight increases in total recharge. Third, mountain system recharge is expected to decline across much of the region due to decreased snowpack, with that impact lessening with higher elevation and latitude. Factors contributing the greatest uncertainty in the estimates include: (1) limited studies quantitatively coupling climate projections to recharge estimation methods using detailed, process-based numerical models; (2) a generally poor understanding of hydrologic flowpaths and processes in mountain systems; (3) difficulty predicting the response of focused recharge to potential changes in the frequency and intensity of extreme precipitation events; and (4) unconstrained feedbacks between climate, irrigation practices, and recharge in highly developed aquifer systems.

Journal of Hydrology↗
USGS2016

Maxent modeling for predicting potential distribution of goitered gazelle in central Iran: the effect of extent and grain size on performance of the model

The spatial scale of environmental layers is an important factor to consider in developing an understanding of ecological processes. This study employed Maxent modeling to investigate the geographic distribution of goitered gazelle, Gazella subgutturosa (Güldenstädt, 1780), in central Iran using uncorrelated variables at a spatial resolution of 250 m. We used spatial downscaling to downscale WorldClim data to 250-m resolution. We evaluated the sensitivity of the model to different grain and extent sizes from 250 m to 3 km. We compared the performance of the model at different scales using suitability indexes (AUC) and predicted habitat areas. Two models performed with AUC values higher than random (AUCun = 0.957, AUCpu = 0.953). The distribution of potential habitats at 250- m grid size was strongly influenced by bioclimatic data, vegetation type and density, and elevation. There were few spatial divergences between uncorrelated and pruned models. The mean AUC across eight different spatial scales ranged from 0.936 to 0.959. There was a significant negative correlation between grain size and AUC (R2 = 0.57). An increase in grain size increased the predicted habitat area. The extent size and AUC showed a positive correlation (R2 = 0.18). Predicted suitability habitat also decreased as extent size increased (R2 = 0.49). Spatial congruence AUC fluctuated within a small range and the maximum difference occurred between models of 1 × 1 and 2.5 × 2.5 km. These results showed that an increase in extent size is more accurate than an increase in grain size, and the maximum accuracy for predicting distribution of goitered gazelle in Iran was obtained if the grain size and extent size were 750 m.

Turkish Journal of Zoology↗
USGS2015

High and dry: high elevations disproportionately exposed to regional climate change in Mediterranean-climate landscapes

Context Predicting climate-driven species’ range shifts depends substantially on species’ exposure to climate change. Mountain landscapes contain a wide range of topoclimates and soil characteristics that are thought to mediate range shifts and buffer species’ exposure. Quantifying fine-scale patterns of exposure across mountainous terrain is a key step in understanding vulnerability of species to regional climate change. Objectives We demonstrated a transferable, flexible approach for mapping climate change exposure in a moisture-limited, mountainous California landscape across 4 climate change projections under phase 5 of the Coupled Model Intercomparison Project (CMIP5) for mid-(2040–2069) and end-of-century (2070–2099). Methods We produced a 149-year dataset (1951–2099) of modeled climatic water deficit (CWD), which is strongly associated with plant distributions, at 30-m resolution to map climate change exposure in the Tehachapi Mountains, California, USA. We defined climate change exposure in terms of departure from the 1951–1980 mean and historical range of variability in CWD in individual years and 3-year moving windows. Results Climate change exposure was generally greatest at high elevations across all future projections, though we encountered moderate topographic buffering on poleward-facing slopes. Historically dry lowlands demonstrated the least exposure to climate change. Conclusions In moisture-limited, Mediterranean-climate landscapes, high elevations may experience the greatest exposure to climate change in the 21st century. High elevation species may thus be especially vulnerable to continued climate change as habitats shrink and historically energy-limited locations become increasingly moisture-limited in the future.

Landscape Ecology↗
USGS2015

Effects of topoclimatic complexity on the composition of woody plant communities

Topography can create substantial environmental variation at fine spatial scales. Shaped by slope, aspect, hill-position and elevation, topoclimate heterogeneity may increase ecological diversity, and act as a spatial buffer for vegetation responding to climate change. Strong links have been observed between climate heterogeneity and species diversity at broader scales, but the importance of topoclimate for woody vegetation across small spatial extents merits closer examination. We established woody vegetation monitoring plots in mixed evergreen-deciduous woodlands that spanned topoclimate gradients of a topographically heterogeneous landscape in northern California. We investigated the association between the structure of adult and regenerating size classes of woody vegetation and multidimensional topoclimate at a fine scale. We found a significant effect of topoclimate on both single-species distributions and community composition. Effects of topoclimate were evident in the regenerating size class for all dominant species (four Quercus spp. , Umbellularia californica and Pseudotsuga menziesii ) but only in two dominant species ( Quercus agrifolia and Quercus garryana ) for the adult size class. Adult abundance was correlated with water balance parameters (e.g. climatic water deficit) and recruit abundance was correlated with an interaction between the topoclimate parameters and conspecific adult abundance (likely reflecting local seed dispersal). However, in all cases, the topoclimate signal was weak. The magnitude of environmental variation across our study site may be small relative to the tolerance of long-lived woody species. Dispersal limitations, management practices and patchy disturbance regimes also may interact with topoclimate, weakening its influence on woody vegetation distributions. Our study supports the biological relevance of multidimensional topoclimate for mixed woodland communities, but highlights that this relationship might be mediated by interacting factors at local scales.

California↗
USGS2015

A framework for effective use of hydroclimate models in climate-change adaptation planning for managed habitats with limited hydrologic response data

Climate-change adaptation planning for managed wetlands is challenging under uncertain futures when the impact of historic climate variability on wetland response is unquantified. We assessed vulnerability of Modoc National Wildlife Refuge (MNWR) through use of the Basin Characterization Model (BCM) landscape hydrology model, and six global climate models, representing projected wetter and drier conditions. We further developed a conceptual model that provides greater value for water managers by incorporating the BCM outputs into a conceptual framework that links modeled parameters to refuge management outcomes. This framework was used to identify landscape hydrology parameters that reflect refuge sensitivity to changes in (1) climatic water deficit (CWD) and recharge, and (2) the magnitude, timing, and frequency of water inputs. BCM outputs were developed for 1981–2100 to assess changes and forecast the probability of experiencing wet and dry water year types that have historically resulted in challenging conditions for refuge habitat management. We used a Yule’s Q skill score to estimate the probability of modeled discharge that best represents historic water year types. CWD increased in all models across 72.3–100 % of the water supply basin by 2100. Earlier timing in discharge, greater cool season discharge, and lesser irrigation season water supply were predicted by most models. Under the worst-case scenario, moderately dry years increased from 10–20 to 40–60 % by 2100. MNWR could adapt by storing additional water during the cool season for later use and prioritizing irrigation of habitats during dry years.

California↗
USGS2015

Targeting climate diversity in conservation planning to build resilience to climate change

Climate change is raising challenging concerns for systematic conservation planning. Are methods based on the current spatial patterns of biodiversity effective given long-term climate change? Some conservation scientists argue that planning should focus on protecting the abiotic diversity in the landscape, which drives patterns of biological diversity, rather than focusing on the distribution of focal species, which shift in response to climate change. Climate is one important abiotic driver of biodiversity patterns, as different climates host different biological communities and genetic pools. We propose conservation networks that capture the full range of climatic diversity in a region will improve the resilience of biotic communities to climate change compared to networks that do not. In this study we used historical and future hydro-climate projections from the high resolution Basin Characterization Model to explore the utility of directly targeting climatic diversity in planning. Using the spatial planning tool, Marxan, we designed conservation networks to capture the diversity of climate types, at the regional and sub-regional scale, and compared them to networks we designed to capture the diversity of vegetation types. By focusing on the Conservation Lands Network (CLN) of the San Francisco Bay Area as a real-world case study, we compared the potential resilience of networks by examining two factors: the range of climate space captured, and climatic stability to 18 future climates, reflecting different emission scenarios and global climate models. We found that the climate-based network planned at the sub-regional scale captured a greater range of climate space and showed higher climatic stability than the vegetation and regional based-networks. At the same time, differences among network scenarios are small relative to the variance in climate stability across global climate models. Across different projected futures, topographically heterogeneous areas consistently show greater climate stability than homogenous areas. The analysis suggests that utilizing high-resolution climate and hydrological data in conservation planning improves the likely resilience of biodiversity to climate change. We used these analyses to suggest new conservation priorities for the San Francisco Bay Area.

Ecosphere↗
USGS2015

Tree mortality predicted from drought-induced vascular damage

The projected responses of forest ecosystems to warming and drying associated with twenty-first-century climate change vary widely from resiliency to widespread tree mortality 1 , 2 , 3 . Current vegetation models lack the ability to account for mortality of overstorey trees during extreme drought owing to uncertainties in mechanisms and thresholds causing mortality 4 , 5 . Here we assess the causes of tree mortality, using field measurements of branch hydraulic conductivity during ongoing mortality in Populus tremuloides in the southwestern United States and a detailed plant hydraulics model. We identify a lethal plant water stress threshold that corresponds with a loss of vascular transport capacity from air entry into the xylem. We then use this hydraulic-based threshold to simulate forest dieback during historical drought, and compare predictions against three independent mortality data sets. The hydraulic threshold predicted with 75% accuracy regional patterns of tree mortality as found in field plots and mortality maps derived from Landsat imagery. In a high-emissions scenario, climate models project that drought stress will exceed the observed mortality threshold in the southwestern United States by the 2050s. Our approach provides a powerful and tractable way of incorporating tree mortality into vegetation models to resolve uncertainty over the fate of forest ecosystems in a changing climate.

Nature Geoscience↗
USGS2015

Integrated climate and land use change scenarios for California rangeland ecosystem services: wildlife habitat, soil carbon, and water supply

Context In addition to biodiversity conservation, California rangelands generate multiple ecosystem services including livestock production, drinking and irrigation water, and carbon sequestration. California rangeland ecosystems have experienced substantial conversion to residential land use and more intensive agriculture. Objectives To understand the potential impacts to rangeland ecosystem services, we developed six spatially explicit (250 m) climate/land use change scenarios for the Central Valley of California and surrounding foothills consistent with three Intergovernmental Panel on Climate Change emission scenario narratives. Methods We quantified baseline and projected change in wildlife habitat, soil organic carbon (SOC), and water supply (recharge and runoff). For six case study watersheds we quantified the interactions of future development and changing climate on recharge, runoff and streamflow, and precipitation thresholds where dominant watershed hydrological processes shift through analysis of covariance. Results The scenarios show that across the region, habitat loss is expected to occur predominantly in grasslands, primarily due to future development (up to a 37 % decline by 2100), however habitat loss in priority conservation errors will likely be due to cropland and hay/pasture expansion (up to 40 % by 2100). Grasslands in the region contain approximately 100 teragrams SOC in the top 20 cm, and up to 39 % of this SOC is subject to conversion by 2100. In dryer periods recharge processes typically dominate runoff. Future development lowers the precipitation value at which recharge processes dominate runoff, and combined with periods of drought, reduces the opportunity for recharge, especially on deep soils. Conclusion Results support the need for climate-smart land use planning that takes recharge areas into account, which will provide opportunities for water storage in dry years. Given projections for agriculture, more modeling is needed on feedbacks between agricultural expansion on rangelands and water supply.

California↗
USGS2015

Storage and mobilization of natural and septic nitrate in thick unsaturated zones, California

Mobilization of natural and septic nitrate from the unsaturated zone as a result of managed aquifer recharge has degraded water quality from public-supply wells near Yucca Valley in the western Mojave Desert, California. The effect of nitrate storage and potential for denitrification in the unsaturated zone to mitigate increasing nitrate concentrations were investigated. Storage of water extractable nitrate in unsaturated alluvium up to 160 meters (m) thick, ranged from 420 to 6600 kilograms per hectare (kg/ha) as nitrogen (N) beneath undeveloped sites, from 6100 to 9200 kg/ha as N beneath unsewered sites. Nitrate reducing and denitrifying bacteria were less abundant under undeveloped sites and more abundant under unsewered sites; however, δ 15 N–NO 3 , and δ 18 O–NO 3 data show only about 5–10% denitrification of septic nitrate in most samples—although as much as 40% denitrification occurred in some parts the unsaturated zone and near the top of the water table. Storage of nitrate in thick unsaturated zones and dilution with low-nitrate groundwater are the primary attenuation mechanisms for nitrate from septic discharges in the study area. Numerical simulations of unsaturated flow, using the computer program TOUGH2, showed septic effluent movement through the unsaturated zone increased as the number and density of the septic tanks increased, and decreased with increased layering, and increased slope of layers, within the unsaturated zone. Managing housing density can delay arrival of septic discharges at the water table, especially in layered unsaturated alluvium, allowing time for development of strategies to address future water-quality issues.

California↗
USGS2015

Climate change: evaluating your local and regional water resources

The BCM is a fine-scale hydrologic model that uses detailed maps of soils, geology, topography, and transient monthly or daily maps of potential evapotranspiration, air temperature, and precipitation to generate maps of recharge, runoff, snow pack, actual evapotranspiration, and climatic water deficit. With these comprehensive environmental inputs and experienced scientific analysis, the BCM provides resource managers with important hydrologic and ecologic understanding of a landscape or basin at hillslope to regional scales. The model is calibrated using historical climate and streamflow data over the range of geologic materials specific to an area. Once calibrated, the model is used to translate climate-change data into hydrologic responses for a defined landscape, to provide managers an understanding of potential ecological risks and threats to water supplies and managed hydrologic systems. Although limited to estimates of unimpaired hydrologic conditions, estimates of impaired conditions, such as agricultural demand, diversions, or reservoir outflows can be incorporated into the calibration of the model to expand its utility. Additionally, the model can be linked to other models, such as groundwater-flow models (that is, MODFLOW) or the integrated hydrologic model (MF-FMP), to provide information about subsurface hydrologic processes. The model can be applied at a relatively small scale, but also can be applied to large-scale national and international river basins.

Fact Sheet↗
USGS2015

The source, discharge, and chemical characteristics of selected springs, and the abundance and health of associated endemic anuran species in the Mojave network parks

Hydrological and biological investigations were done during 2005 and 2006 in cooperation with the U.S. National Park Service to investigate the source, discharge, and chemical characteristics of selected springs and the abundance and health of endemic anuran (frog and toad) species at Darwin Falls in Death Valley National Park, Piute Spring in Mojave National Preserve, and Fortynine Palms Oasis in Joshua Tree National Park. Discharge from the springs at these sites sustains isolated riparian habitats in the normally dry Mojave Desert. Data were collected on water quantity (discharge) and quality, air and water temperature, and abundance and health of endemic anuran species. In addition, a single survey of the abundance and health of endemic anuran species was completed at Rattlesnake Canyon in Joshua Tree National Park. Results from this study were compared to limited historical data, where they exist, and can provide a baseline for future hydrological and biological investigations to evaluate the health and sustainability of the resource and its response to changing climate and increasing human use. Radiocarbon dating of the water yielded estimated ages of about 7,000 years at Piute Spring and about 3,000 years at Darwin Spring, and tritium-helium-3 dating indicated an age of less than 2 years at Fortynine Palms Oasis. Stable hydrogen-isotope ratios were used to interpret an average altitude of recharge of 2,348 meters for Darwin Spring (about 1,415 meters higher than the altitude of Darwin Spring), 1,668 meters for Piute Spring (about 766 meters higher than the altitude of Piute Spring), and 1,400 meters for the Upper Pool at Fortynine Palms Oasis (about 543 meters higher than the altitude of the Upper Pool). Water-quality data collected for this study did not appear to be sensitive to trends in precipitation or seasonality in the Darwin Falls and Piute Spring study areas; however, it was sensitive to trends in Fortynine Palms Oasis where salinity increased by more than 10 percent during the 2 years of this study. Such a rapid response is consistent with the comparatively short travel time of less than 2 years from recharge to discharge at Fortynine Palms Oasis. Of the 14 trace elements analyzed, only concentrations of uranium at Fortynine Palms Oasis and arsenic at Darwin Spring were above drinking water standards; both constituents are derived from natural sources in the drainage basin and, therefore, are likely to have accumulated as a result of natural processes. Endemic anuran species were surveyed at Darwin Falls for the western toad ( Anaxyrus boreas ) and the red-spotted toad ( Anaxyrus punctatus ), at Piute Spring for the red-spotted toad, and at Fortynine Palms Oasis for the red-spotted toad and California treefrog ( Pseudacris cadaverina ). Historically, red-spotted toads were at the edge of their range at Darwin Falls, but they were not detected during this study and have not been detected since the early 1980s. The 2006 western toad population at Darwin Falls was estimated at 381 adults (95-percent confidence interval [CI] of 314–482). The population of red-spotted toads at Piute Spring was estimated at 1,153 adults (95-percent CI of 935–1,503). However, an elevated rate of abnormalities (approximately 5 percent) was recorded in red-spotted toads as well as the presence of the chytrid fungus, Bactrochochytrium dendrobatidis , at Piute Spring. In Joshua Tree National Park, the California treefrog now occupies only three of the seven historically occupied drainages. Populations of California treefrogs at Fortynine Palms Oasis have declined more than 50 percent from 288 in 1969–71 to 109 in 2006. A similar decline was observed in the populations of red-spotted toads at Fortynine Palms Oasis from 300 adults in 1969–71 to 155 adults (95-percent CI of 90–139) in 2006. The red-spotted toads at Fortynine Palms Oasis also exhibited the presence of Bactrochochytrium dendrobatidis .

California↗
USGS2014

Topographic, latitudinal and climatic distribution of Pinus coulteri : geographic range limits are not at the edge of the climate envelope

With changing climate, many species are projected to move poleward or to higher elevations to track suitable climates. The prediction that species will move poleward assumes that geographically marginal populations are at the edge of the species' climatic range. We studied Pinus coulteri from the center to the northern (poleward) edge of its range, and examined three scenarios regarding the relationship between the geographic and climatic margins of a species' range. We used herbarium and iNaturalist.org records to identify P. coulteri sites, generated a species distribution model based on temperature, precipitation, climatic water deficit, and actual evapotranspiration, and projected suitability under future climate scenarios. In fourteen populations from the central to northern portions of the range, we conducted field studies and recorded elevation, slope and aspect (to estimate solar insolation) to examine relationships between local and regional distributions. We found that northern populations of P. coulteri do not occupy the cold or wet edge of the species' climatic range; mid-latitude, high elevation populations occupy the cold margin. Aspect and insolation of P. coulteri populations changed significantly across latitudes and elevations. Unexpectedly, northern, low-elevation stands occupy north-facing aspects and receive low insolation, while central, high-elevation stands grow on more south-facing aspects that receive higher insolation. Modeled future climate suitability is projected to be highest in the central, high elevation portion of the species range, and in low-lying coastal regions under some scenarios, with declining suitability in northern areas under most future scenarios. For P. coulteri , the lack of high elevation habitat combined with a major dispersal barrier may limit northward movement in response to a warming climate. Our analyses demonstrate the importance of distinguishing geographically vs. climatically marginal populations, and the importance of quantitative analysis of the realized climate space to understand species range limits.

Ecography↗
USGS2014

Incorporating cold-air pooling into downscaled climate models increases potential refugia for snow-dependent species within the Sierra Nevada Ecoregion, CA

We present a unique water-balance approach for modeling snowpack under historic, current and future climates throughout the Sierra Nevada Ecoregion. Our methodology uses a finer scale (270 m) than previous regional studies and incorporates cold-air pooling, an atmospheric process that sustains cooler temperatures in topographic depressions thereby mitigating snowmelt. Our results are intended to support management and conservation of snow-dependent species, which requires characterization of suitable habitat under current and future climates. We use the wolverine ( Gulo gulo ) as an example species and investigate potential habitat based on the depth and extent of spring snowpack within four National Park units with proposed wolverine reintroduction programs. Our estimates of change in spring snowpack conditions under current and future climates are consistent with recent studies that generally predict declining snowpack. However, model development at a finer scale and incorporation of cold-air pooling increased the persistence of April 1st snowpack. More specifically, incorporation of cold-air pooling into future climate projections increased April 1st snowpack by 6.5% when spatially averaged over the study region and the trajectory of declining April 1st snowpack reverses at mid-elevations where snow pack losses are mitigated by topographic shading and cold-air pooling. Under future climates with sustained or increased precipitation, our results indicate a high likelihood for the persistence of late spring snowpack at elevations above approximately 2,800 m and identify potential climate refugia sites for snow-dependent species at mid-elevations, where significant topographic shading and cold-air pooling potential exist.

California↗
USGS2014

Hydroclimate of the Spring Mountains and Sheep Range, Clark County, Nevada

Precipitation, potential evapotranspiration, and actual evapotranspiration often are used to characterize the hydroclimate of a region. Quantification of these parameters in mountainous terrains is difficult because limited access often hampers the collection of representative ground data. To fulfill a need to characterize ecological zones in the Spring Mountains and Sheep Range of southern Nevada, spatially and temporally explicit estimates of these hydroclimatic parameters are determined from remote-sensing and model-based methodologies. Parameter-elevation Regressions on Independent Slopes Model (PRISM) precipitation estimates for this area ranges from about 100 millimeters (mm) in the low elevations of the study area (700 meters [m]) to more than 700 mm in the high elevations of the Spring Mountains (> 2,800 m). The PRISM model underestimates precipitation by 7–15 percent based on a comparison with four high‑elevation precipitation gages having more than 20 years of record. Precipitation at 3,000-m elevation is 50 percent greater in the Spring Mountains than in the Sheep Range. The lesser amount of precipitation in the Sheep Range is attributed to partial moisture depletion by the Spring Mountains of eastward-moving, cool-season (October–April) storms. Cool-season storms account for 66–76 percent of annual precipitation. Potential evapotranspiration estimates by the Basin Characterization Model range from about 700 mm in the high elevations of the Spring Mountains to 1,600 mm in the low elevations of the study area. The model realistically simulates lower potential evapotranspiration on northeast-to-northwest facing slopes compared to adjacent southeast-to-southwest facing slopes. Actual evapotranspiration, estimated using a Moderate Resolution Imaging Spectroradiometer based water-balance model, ranges from about 100 to 600 mm. The magnitude and spatial variation of simulated, actual evapotranspiration was validated by comparison to PRISM precipitation. Estimated groundwater recharge, computed as the residual of precipitation depleted by actual evapotranspiration, is within the range of previous estimates. A climatic water deficit dataset and aridity-index-based climate zones are derived from precipitation and evapotranspiration datasets. Climate zones range from arid in the lower elevations of the study area to humid in small pockets on north- to northeast-facing slopes in the high elevations of the Spring Mountains. Correlative analyses between hydroclimatic variables and mean ecosystem elevations indicate that the climatic water deficit is the best predictor of ecosystem distribution (R 2 = 0.92). Computed water balances indicate that substantially more recharge is generated in the Spring Mountains than in the Sheep Range. A geospatial database containing compiled and developed hydroclimatic data and other pertinent information accompanies this report.

Nevada↗
USGS2013

Effects of climate change and urban development on the distribution and conservation of vegetation in a Mediterranean type ecosystem

Climate and land-use changes are projected to threaten biodiversity over this century. However, few studies have considered the spatial and temporal overlap of these threats to evaluate how ongoing land-use change could affect species ranges projected to shift outside conservation areas. We evaluated climate change and urban development effects on vegetation distribution in the Southwest ecoregion, California Floristic Province, USA. We also evaluated how well a conservation network protects suitable habitat for rare plant species under these change projections and identified primary sources of uncertainty. We used consensus-based maps from three species distribution models (SDMs) to project current and future suitable habitat for 19 species representing different functional types (defined by fire-response – obligate seeders, resprouting shrubs – and life forms – herbs, subshrubs), and range sizes (large/common, small/rare). We used one spatially explicit urban growth projection; two climate models, emission scenarios, and probability thresholds applied to SDMs; and high-resolution (90 m) environmental data. We projected that suitable habitat could disappear for 4 species and decrease for 15 by 2080. Averaged centroids of suitable habitat (all species) were projected to shift tens (up to hundreds) of kilometers. Herbs showed a small-projected response to climate change, while obligate seeders could suffer the greatest losses. Several rare species could lose suitable habitat inside conservation areas while increasing area outside. We concluded that (i) climate change is more important than urban development for vegetation habitat loss in this ecoregion through 2080 due to diminishing amounts of undeveloped private land in this region; (ii) the existing conservation plan, while extensive, may be inadequate to protect plant diversity under projected patterns of climate change and urban development, (iii) regional assessments of the dynamics of the drivers of biodiversity change based on high-resolution environmental data and consensus predictive mapping, such as this study, are necessary to identify the species expected to be the most vulnerable and to meaningfully inform regional-scale conservation.

California↗