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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 307 records · Page 17Linked to original sources
USGS2011

Rising sea level may cause decline of fringing coral reefs

Coral reefs are major marine ecosystems and critical resources for marine diversity and fisheries. These ecosystems are widely recognized to be at risk from a number of stressors, and added to those in the past several decades is climate change due to anthropogenically driven increases in atmospheric concentrations of greenhouse gases. Most threatening to most coral reefs are elevated sea surface temperatures and increased ocean acidity [e.g., Kleypas et al., 1999; Hoegh-Guldberg et al., 2007], but sea level rise, another consequence of climate change, is also likely to increase sedimentary processes that potentially interfere with photosynthesis, feeding, recruitment, and other key physiological processes (Figure 1). Anderson et al. [2010] argue compellingly that potential hazardous impacts to coastlines from 21st-century sea level rise are greatly underestimated, particularly because of the rapid rate of rise. The Intergovernmental Panel on Climate Change estimates that sea level will rise in the coming century (1990–2090) by 2.2–4.4 millimeters per year, when projected with little contribution from melting ice [Meehl et al., 2007]. New studies indicate that rapid melting of land ice could substantially increase the rate of sea level rise [Grinsted et al., 2009; Milne et al., 2009].

Eos, Transactions, American Geophysical Union↗
USGS2003

Large-scale phytogeographical patterns in East Asia in relation to latitudinal and climatic gradients

Aim: This paper aims at determining how different floristic elements (e.g. cosmopolitan, tropical, and temperate) change with latitude and major climate factors, and how latitude affects the floristic relationships between East Asia and the other parts of the world. Location: East Asia from the Arctic to tropical regions, an area crossing over 50?? of latitudes and covering the eastern part of China, Korea, Japan and the eastern part of Russia. Methods: East Asia is divided into forty-five geographical regions. Based on the similarity of their world-wide distributional patterns, a total of 2808 indigenous genera of seed plants found in East Asia were grouped into fourteen geographical elements, belonging to three major categories (cosmopolitan, tropical and temperate). The 50??-long latitudinal gradient of East Asia was divided into five latitudinal zones, each of c. 10??. Phytogeographical relationships of East Asia to latitude and climatic variables were examined based on the forty-five regional floras. Results: Among all geographical and climatic variables considered, latitude showed the strongest relationship to phytogeographical composition. Tropical genera (with pantropical, amphi-Pacific tropical, palaeotropical, tropical Asia-tropical Australia, tropical Asia-tropical Africa and tropical Asia geographical elements combined) accounted for c. 80% of the total genera at latitude 20??N and for c. 0% at latitude 55-60??N. In contrast, temperate genera (including holarctic, eastern Asia-North America, temperate Eurasia, temperate Asia, Mediterranean, western Asia to central Asia, central Asia and eastern Asia geographical elements) accounted for 15.5% in the southernmost latitude and for 80% at 55-60??N, from where northward the percentage tended to level off. The proportion of cosmopolitan genera increased gradually with latitude from 5% at the southernmost latitude to 21% at 55-60??N, where it levelled off northward. In general, the genera present in a more northerly flora are a subset of the genera present in a more southerly flora. Main conclusions: The large-scale patterns of phytogeography in East Asia are strongly related to latitude, which covaries with several climatic variables such as temperature. Evolutionary processes such as the adaptation of plants to cold climates and current and past land connections are likely responsible for the observed latitudinal patterns.

Journal of Biogeography↗
USGS2007

1400 yr multiproxy record of climate variability from the northern Gulf of Mexico

A continuous decadal-scale resolution record of climate variability over the past 1400 yr in the northern Gulf of Mexico was constructed from a box core recovered in the Pigmy Basin, northern Gulf of Mexico. Proxies include paired analyses of Mg/Ca and δ 18 O in the white variety of the planktic foraminifer Globigerinoides ruber and relative abundance variations of G. sacculifer in the foraminifer assemblages. Two multi-decadal intervals of sustained high Mg/Ca indicate that Gulf of Mexico sea surface temperatures (SSTs) were as warm or warmer than near-modern conditions between 1000 and 1400 yr B.P. Foraminiferal Mg/Ca during the coolest interval of the Little Ice Age (ca. 250 yr B.P.) indicate that SST was 2–2.5 °C below modern SST. Four minima in the Mg/Ca record between 900 and 250 yr B.P. correspond with the Maunder, Spörer, Wolf, and Oort sunspot minima, suggesting a link between changes in solar insolation and SST variability in the Gulf of Mexico. An abrupt shift recorded in both δ 18 O calcite and relative abundance of G. sacculifer occurred ca. 600 yr B.P. The shift in the Pigmy Basin record corresponds with a shift in the sea-salt-sodium (ssNa) record from the Greenland Ice Sheet Project 2 ice core, linking changes in high-latitude atmospheric circulation with the subtropical Atlantic Ocean.

Geology↗
USGS2024

Testing tree-ring cellulose δ18O with water isotopes for Holocene lake δ18O interpretations in the central Rocky Mountains USA

Stable isotopes of water preserved in geologic archives, primarily as oxygen (δ18O), have proven critical for documenting Earth’s climatic and hydrologic systems past and present. However, timescale differences of water isotope inputs to proxy systems and the signal embedded in long paleorecords often confound translation to observed hydroclimatic metrics. Here, a unique 20-year dataset of meteorology, hydrology, and the isotopic composition of weekly meteoric and surface water samples (δ18O, δ2 H) are combined with paleoclimate δ18O data from tree-ring cellulose and lake carbonate to better understand proxy signals of Upper Colorado river basin drought. Annual tree-ring cellulose δ18O from Picea engelmannii growing within a glacier-fed creek and a spring discharge area were used to derive annual source water δ18O using a cellulose source-water isotope model. Comparisons with the monitoring record indicates that tree-ring cellulose δ18O tracks variations in wet and dry hydroclimatic extremes. Source water isotopes are shown to reflect the hydroclimate of the current year and some number of previous years as an effective moisture-discharge proxy rather than a precipitation isotope proxy. Results contextualize Holocene lake carbonate δ18O data. The contemporary-to-paleo comparison identifies changes in seasonal precipitation extremes during recent millennia and several earlier arid and monsoon-dominated Holocene periods that exceed the arid maximum of the calibration period.

Colorado↗
USGS2004

Annual layers revealed by GPR in the subsurface of a prograding coastal barrier, southwest Washington, U.S.A

The southwest Washington coastline has experienced extremely high rates of progradation during the late Holocene. Subsurface stratigraphy, preserved because of progradation and interpreted using ground-penetrating radar (GPR), has previously been used successfully to document coastal response to prehistoric storm and earthquake events. New GPR data collected at Ocean Shores, Washington, suggest that the historic stratigraphy of the coastal barrier in this area represents a higher resolution record of coastal behavior than previously thought. GPR records for this location at 200 MHz reveal a series of gently sloping, seaward-dipping reflections with slopes similar to the modern beach and spacings on the order of 20-45 cm. Field evidence and model results suggest that thin (1-10 cm), possibly magnetite-rich, heavy-mineral lags or low-porosity layers left by winter storms and separated by thick (20-40 cm) summer progradational sequences are responsible for generating the GPR reflections. These results indicate that a record of annual progradation is preserved in the subsurface of the prograding barrier and can be quantified using GPR. Such records of annual coastal behavior, where available, will be invaluable in understanding past coastal response to climatic and tectonic forcing.

Washington↗
USGS2016

Data, age uncertainties and ocean δ 18 O under the spotlight for Ocean2k Phase 2

The oceans make up 71% of the Earth’s surface area and are a major component of the global climate system. They are the world’s primary heat reservoir, and knowledge of the global ocean response to past and present radiative forcing is important for understanding climate change. PAGES’ Ocean2k working group aims to place marine climate of the past century within the context of the previous 2000 years (2k). Phase 1 (2011-2015) focused on constraining the forcing mechanisms most consistent with reconstructed sea surface temperature (SST) over the 2k interval (McGregor et al. 2015; Tierney et al. 2015). The 1st Ocean2k workshop assisted in the transition to Ocean2k Phase 2 (2015-2017), with the workshop goal to develop, coordinate and significantly advance community-identified and -driven activities.

Past Global Changes↗
USGS1997

How Does Climate Change Influence Alaska's Vegetation?: Insights from the Fossil Record

Plant fossils, such as leaves, wood, cones, pollen, and seeds, provide important evidence of how Alaska's vegetation has responded to climate changes over time periods of centuries to millions of years. Long-term trends of global temperatures have been reconstructed from oxygen isotope measurements of microscopic fossils (foraminifera) in the Pacific Ocean (fig. 1) . This temperature curve can be used to compare the major changes in Alaskan vegetation with global climate changes spanning the past 20 million years.

Fact Sheet↗
USGS2004

Anthropogenic and natural variation in ridge and slough pollen assemblages

We present pollen evidence documenting the response of sawgrass ridge and slough systems of the Florida Everglades to hydrologic changes during the last 3,500 years. Sediment cores and surface samples were collected in three transects across sawgrass ridges and sloughs in Water Conservation Area 3A to determine the age of the features, long-term variability in plant community composition, stability of sawgrass ridge and slough size, and their response to 20th century changes in hydrology. Statistically significant differences in abundance of Cladium pollen in surface samples collected throughout the system allow differentiation of these communities in the sedimentary pollen record. Analysis of pollen in cores from the three transects indicates that the general distribution of ridges and sloughs has remained distinct through time. There is evidence the vegetation has responded to past global-scale climate events, such as the Medieval Warm Period, as well as the 20th century anthropogenic alterations to the natural hydrology. The ridge community is more responsive and susceptible to perturbations in hydrology than the slough community. In contrast, the slough plant community is more stable and less likely to demonstrate long-term changes after perturbations to hydrology. Regardless, these data indicate that the ridge and slough landscape is resilient to changes in hydrology and posses the potential to return to a natural state with the return of natural hydrologic conditions.

Florida↗
USGS2003

Large-scale phytogeographical patterns in eastern Asia in relation to latitudinal and climatic gradients

This paper aims at determining how different floristic elements (e.g. cosmopolitan, tropical, and temperate) change with latitude and major climate factors, and how latitude affects the floristic relationships between East Asia and the other parts of the world. The large-scale patterns of phytogeography in East Asia are strongly related to latitude, which covaries with several climatic variables such as temperature. Evolutionary processes such as the adaptation of plants to cold climates and current and past land connections are likely responsible for the observed latitudinal patterns.

Journal of Biogeography↗
USGS2003

Endangered toads in the Rockies

The western toad species complex, endemic to western North America, includes two montane species that have undergone extensive declines. These are the Yosemite toad, Bufo canorus, in the Sierra Nevada, and the southern Rocky Mountain populations of the boreal toad, B. borea. Most declines in the Rockies appear to have occurred before 1980, but a recent episode in Rocky Mountain National Park illustrates the rapidity and severity with which populations of toads can succumb, and that the phenomenon is still occurring. Causes of these declines, with experimental or observational support, include increasing ultraviolet radiation; disease; and interactions among several factors. However, significant questions about the generality of each of these hypotheses remain to be answered. Regardless of the cause of past and current declines, climate change in the coming decades may create conditions that will challenge the persistence of these species, and others not currently threatened.

Rocky Mountains↗
USGS1989

Studies of geology and hydrology in the Basin and Range Province, Southwestern United States, for isolation of high-level radioactive waste - Basis of characterization and evaluation

The geologic and hydrologic factors in selected regions of the Basin and Range province were examined to identify prospective areas for further study that may provide isolation of high-level radioactive waste from the accessible environment. The six regions selected for study were characterized with respect to the following guidelines: (1) Potential repository media; (2) Quaternary tectonic conditions; (3) climatic change and geomorphic processes; (4) ground-water conditions; (5) ground-water quality; and (6) mineral and energy resources. The repository medium will function as the first natural barrier to radionuclide travel by virtue of associated slow ground-water velocity. The principal rock types considered as host media include granitic, intermediate, and mafic intrusive rocks; argillaceous rocks; salt and anhydrite; volcanic mudflow (laharic) breccias; some intrusive rhyolitic plugs and stocks; partially zeolitized tuff; and metamorphic rocks. In the unsaturated zone, the permeability and hydrologic properties of the rocks and the hydrologic setting are more important than the rock type. Media ideally should be permeable to provide drainage and should have a minimal water flux The ground-water flow path from a repository to the accessible environment needs to present major barriers to the transport of radionuclides. Factors considered in evaluating the ground-water conditions include ground-water traveltimes and quality, confining beds, and earth materials favorable for retardation of radionuclides. Ground-water velocities in the regions were calculated from estimated hydraulic properties of the rocks and gradients. Because site-specific data on hydraulic properties are not available, data from the literature were assembled and synthesized to obtain values for use in estimating ground-water velocities. Hydraulic conductivities for many rock types having granular and fracture permeability follow a log-normal distribution. Porosity for granular and very weathered crystalline rock tends to be normally distributed; porosity of fractured crystalline rock probably follows a log-normal distribution. The tectonic setting needs to prevent an increase in radionuclides to the accessible environment. Data on historic seismicity and heat flow, Quaternary faults, volcanism, and uplift were used to assess the tectonic conditions. Long-term late Cenozoic rates of vertical crustal movement in the Basin and Range province range from less than 2 meters per 104 years to greater than 20 meters per 104 years. Shortterm rates of vertical movement may be more than an order of magnitude greater, based on geodetic leveling. Changes in tectonic and climatic processes may potentially cause changes in hydrologic conditions and geomorphology that could affect the integrity of a deep, mined repository either adversely or beneficially. The transition from a full-glacial climate to the current interglacial condition has occurred within the past 15,000 years. Reconstructions of the last full-glacial climate indicate that, at that time, there was greater water availability for runoff and vegetation growth than there is now. Based on the increased water availability and depending on seasonal distribution of precipitation, on soil characteristics, on topography, and on other characteristics, ground-water recharge during the full-glacial climate is estimated to have been possibly 2 to 10 or more times the modern rate. During the full-glacial climate, more than 100 lakes occupied closed basins in the province. Any increase in ground-water recharge and refilling of Pleistocene lakes will tend to decrease the distance of ground-water flow and its time of travel. The unsaturated zone this zone is considered a potential host medium where the thickness is greater than 150 m will be decreased by these changes. In contrast, incision of streams and other geomorphic, tectonic, or climatically induced changes that lower the ground-water discharge level will tend to increase the thickness of the unsaturated zone. Aggradation in basinal troughs may either decrease or increase the thickness of the unsaturated zone. Aggradation in basins that causes the ground-water discharge level to rise will tend to decrease the thickness of unsaturated zone in the adjacent uplands; aggradation in basins where the ground-water discharge level remains the same or is lowered will increase the unsaturated thickness of basin fill. Records show that, throughout late Cenozoic time in the Basin and Range province, continued vertical crustal movements have tended to maintain mountain ranges and closed basins, whereas aggradation of the basins and erosion of the mountain ranges have tended to decrease the topographic relief. Maximum rates of denudation for small basins in areas climatically similar to the Basin and Range province are about 2 meters per 104 years. For sites unaffected by stream incision and scarp retreat, a conservative estimate of erosion affecting long-term changes in depth of burial would appear to be 2 meters per 104 years, or, equal to the long-term rate of vertical crustal movement where greater than 2 meters per 104 years. The response of the ground-water conditions to climatic and geomorphically induced boundary conditions is significant from the points of: (1) The potential maximum change in the ground-water flow system; (2) the time of response of the ground-water system; and (3) the present state of the ground-water system as a result of past changes. Effects of longterm climatic and tectonic changes on hydrologic and geomorphic conditions differ from area to area, and rates of change of geomorphic and hydrologic conditions may vary significantly. Therefore, sitespecific studies need to be made to assess the long-term integrity of deep, mined repositories.

Arizona, California, Idaho, Nevada, New Mexico, Te↗
USGS1973

Stability of salt in the Permian salt basin of Kansas, Oklahoma, Texas, and New Mexico, with a section on dissolved salts in surface water

The Permian salt basin in the Western Interior of the United States is defined as that region comprising a series of sedimentary basins in which halite and associated salts accumulated during Permian time. The region includes the western parts of Kansas, Oklahoma, and Texas, and eastern parts of Colorado and New Mexico. Following a long period of general tectonic stability throughout the region during most of early Paleozoic time, there was much tectonic activity in the area of the Permian salt basin during Late Pennsylvanian and Early Permian time just before bedded salt was deposited. The Early Permian tectonism was followed by stabilization of the basins in which the salt was deposited. These salt basins were neither contemporaneous nor continuous throughout the region, so that many salt beds are also discontinuous. In general, beds in the northern part of the basin (Kansas and northern Oklahoma) are older and the salt is progressively younger towards the south. Since Permian time the Permian salt basin has been relatively stable tectonically. Regionally, the area of the salt basin has been tilted and warped, has undergone periods of erosion, and has been subject to a major incursion of the sea; but deep-seated faults or igneous intrusions that postdate Permian salt are rare. In areas of the salt basin where salt is near the surface, such as southeastern New Mexico and central Kansas, there are no indications of younger deep-seated faulting and only a few isolated igneous intrusives of post-Permian age. On the other hand, subsidence or collapse of the land surface resulting from dissolution has been commonplace in the Permian salt basin. Some dissolution of salt deposits has probably been taking place ever since deposition of the salt more than 230 million years ago. Nevertheless, the subsurface dissolution fronts of the thick bedded-salt deposits of the Permian basin have retreated at a very slow average rate during that 230 million years. The preservation of bedded salt from subsurface dissolution depends chiefly on the isolation of the salt from moving ground water that is not completely saturated with salt. Karst topography is a major criterion for recognizing areas where subsurface dissolution has been active in the past; therefore, the age of the karst development is needed to provide the most accurate estimate of the dissolution rate. The Ogallala Formation-of Pliocene age is probably the most widespread deposit in the Permian salt basin that can be used as a point of reference for dating the development of recent topography. It is estimated that salt has been dissolved laterally in the vicinity of Carlsbad, New Mexico, at an average rate of about 6-8 miles per million years. Estimates of future rates of salt dissolution and the resulting lateral retreat of the underground dissolution front can be projected with reasonable confidence for southeastern New Mexico on the assumption that the climatic changes there in the past 4 million years are representative of climatic changes that may be expected in the near future of geologic time. Large amounts of salt are carried by present-day rivers in the Permian salt basin; some of the salt is derived from subsurface salt beds, but dissolution is relatively slow. Ground-water movement through the Permian salt basin is also relatively slow.

Kansas, New Mexico, Oklahoma, Texas↗
USGS2011

Sensitivity of Pliocene ice sheets to orbital forcing

The stability of the Earth's major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0 million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (Jansen et al., 2007). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25 m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not correspond to orbital maxima, but occurs at times where the anti-phasing of Northern and Southern Hemisphere ice sheet retreat is minimised.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2016

Understanding the past to interpret the future: Comparison of simulated groundwater recharge in the upper Colorado River basin (USA) using observed and general-circulation-model historical climate data

In evaluating potential impacts of climate change on water resources, water managers seek to understand how future conditions may differ from the recent past. Studies of climate impacts on groundwater recharge often compare simulated recharge from future and historical time periods on an average monthly or overall average annual basis, or compare average recharge from future decades to that from a single recent decade. Baseline historical recharge estimates, which are compared with future conditions, are often from simulations using observed historical climate data. Comparison of average monthly results, average annual results, or even averaging over selected historical decades, may mask the true variability in historical results and lead to misinterpretation of future conditions. Comparison of future recharge results simulated using general circulation model (GCM) climate data to recharge results simulated using actual historical climate data may also result in an incomplete understanding of the likelihood of future changes. In this study, groundwater recharge is estimated in the upper Colorado River basin, USA, using a distributed-parameter soil-water balance groundwater recharge model for the period 1951–2010. Recharge simulations are performed using precipitation, maximum temperature, and minimum temperature data from observed climate data and from 97 CMIP5 (Coupled Model Intercomparison Project, phase 5) projections. Results indicate that average monthly and average annual simulated recharge are similar using observed and GCM climate data. However, 10-year moving-average recharge results show substantial differences between observed and simulated climate data, particularly during period 1970–2000, with much greater variability seen for results using observed climate data.

Upper Colorado River basin↗
USGS2008

Abrupt climate change and collapse of deep-sea ecosystems

We investigated the deep-sea fossil record of benthic ostracodes during periods of rapid climate and oceanographic change over the past 20,000 years in a core from intermediate depth in the northwestern Atlantic. Results show that deep-sea benthic community "collapses" occur with faunal turnover of up to 50% during major climatically driven oceanographic changes. Species diversity as measured by the Shannon-Wiener index falls from 3 to as low as 1.6 during these events. Major disruptions in the benthic communities commenced with Heinrich Event 1, the Inter-Aller??d Cold Period (IACP: 13.1 ka), the Younger Dryas (YD: 12.9-11.5 ka), and several Holocene Bond events when changes in deep-water circulation occurred. The largest collapse is associated with the YD/IACP and is characterized by an abrupt two-step decrease in both the upper North Atlantic Deep Water assemblage and species diversity at 13.1 ka and at 12.2 ka. The ostracode fauna at this site did not fully recover until ???8 ka, with the establishment of Labrador Sea Water ventilation. Ecologically opportunistic slope species prospered during this community collapse. Other abrupt community collapses during the past 20 ka generally correspond to millennial climate events. These results indicate that deep-sea ecosystems are not immune to the effects of rapid climate changes occurring over centuries or less. ?? 2008 by The National Academy of Sciences of the USA.

Proceedings of the National Academy of Sciences of↗
USGS1993

Hydro-Climatic Data Network (HCDN) Streamflow Data Set, 1874-1988

The potential consequences of climate change to continental water resources are of great concern in the management of those resources. Critically important to society is what effect fluctuations in the prevailing climate may have on hydrologic conditions, such as the occurrence and magnitude of floods or droughts and the seasonal distribution of water supplies within a region. Records of streamflow that are unaffected by artificial diversions, storage, or other works of man in or on the natural stream channels or in the watershed can provide an account of hydrologic responses to fluctuations in climate. By examining such records given known past meteorologic conditions, we can better understand hydrologic responses to those conditions and anticipate the effects of postulated changes in current climate regimes. Furthermore, patterns in streamflow records can indicate when a change in the prevailing climate regime may have occurred in the past, even in the absence of concurrent meteorologic records. A streamflow data set, which is specifically suitable for the study of surface-water conditions throughout the United States under fluctuations in the prevailing climatic conditions, has been developed. This data set, called the Hydro-Climatic Data Network, or HCDN, consists of streamflow records for 1,659 sites throughout United States and its Territories. Records cumulatively span the period 1874 through 1988, inclusive, and represent a total of 73,231 water years of information. Development of the HCDN Data Set: Records for the HCDN were obtained through a comprehensive search of the extensive surface- water data holdings of the U.S. Geological Survey (USGS), which are contained in the USGS National Water Storage and Retrieval System (WATSTORE). All streamflow discharge records in WATSTORE through September 30, 1988, were examined for inclusion in the HCDN in accordance with strictly defined criteria of measurement accuracy and natural conditions. No reconstructed records of 'natural flow' were permitted, nor was any record extended or had missing values 'filled in' using computational algorithms. If the streamflow at a station was judged to be free of controls for only a part of the entire period of record that is available for the station, then only that part was included in the HCDN, but only if it was of sufficient length (generally 20 years) to warrant inclusion. In addition to the daily mean discharge values, complete station identification information and basin characteristics were retrieved from WATSTORE for inclusion in the HCDN. Statistical characteristics, including the monthly mean discharge, as well as the annual mean, minimum and maximum discharge values, were derived for the records in the HCDN data set. For a full description of the development and content of the Hydro-Climatic Data Network, please take a look at the HCDN Report.

Water-Resources Investigations Report↗
USGS2012

The past as prelude to the future for understanding 21st-century climate effects on Rocky Mountain Trout

Bioclimatic models predict large reductions in native trout across the Rocky Mountains in the 21st century but lack details about how changes will occur. Through five case histories across the region, we explore how a changing climate has been affecting streams and the potential consequences for trout. Monitoring records show trends in temperature and hydrographs consistent with a warming climate in recent decades. Biological implications include upstream shifts in thermal habitats, risk of egg scour, increased wildfire disturbances, and declining summer habitat volumes. The importance of these factors depends on the context, but temperature increases are most relevant where population boundaries are mediated by thermal constraints. Summer flow declines and wildfires will be important where trout populations are fragmented and constrained to small refugia. A critical information gap is evidence documenting how populations are adjusting to long-term habitat trends, so biological monitoring is a priority. Biological, temperature, and discharge data from monitoring networks could be used to develop accurate vulnerability assessments that provide information regarding where conservation actions would best improve population resilience. Even with better information, future uncertainties will remain large due to unknowns regarding Earth's ultimate warming trajectory and how effects translate across scales. Maintaining or increasing the size of habitats could provide a buffer against these uncertainties.

Fisheries↗
USGS1963

Simple measurements of morphological changes in river channels and hillslopes

One of the principal types of observational evidence on climatic changes in the recent geologic past is in river position and elevation. It is well known that river channels, particularly those flowing through alluvium or on relatively soft bedrock, tend to develop flood plains by lateral migration of the channel. Abandoned flood plains at elevations distinctly above the present river channel are the origin of river terraces, widespread through the world but particularly noticeable in arid regions. Climatic change is one of the causes of the abandonment of flood plains and the consequent formation of river terraces. Therefore, the identification and stratigraphy of river terraces is one of the methods by which climatic changes in the recent geologic past can be studied. There are, of course, morphologic changes in river channels of a more subtle nature. Even when a channel is progressively degrading-a trend which will eventually result in the formation of a river terracethere are no obvious criteria by which the current changes in a river channel can be positively identified. For this reason simple techniques, which will aid in the direct observation of current changes in a channel’s position, can be helpful in identifying the nature of changes in progress. It is the purpose of this paper to describe some relatively simple techniques which have been found to be useful in observing morphological changes on slopes and in channels. The methods have been tested primarily in arid climates but to some extent they can also be useful even where vegetation is prominent.

Conference Paper↗