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At least 487 records · Page 27Linked to original sources

USGS2004

A methodology to asess relations between climatic variability and variations in hydrologic time series in the southwestern United States

A new method for frequency analysis of hydrologic time series was developed to facilitate the estimation and reconstruction of individual or groups of frequencies from hydrologic time-series and facilitate the comparison of these isolated time-series components across data types, between different hydrologic settings within a watershed, between watersheds, and across frequencies. While climate-related variations in inflow to and outflow from aquifers have often been neglected, the development and management of ground-water and surface-water resources has required the inclusion of the assessment of the effects of climatic variability on the supply and demand and sustainability of use. The regional assessment of climatic variability of surface-water and ground-water flow throughout the southwestern United States required this new systematic method of hydrologic time-series analysis. To demonstrate the application of this new method, six hydrologic time-series from the Mojave River Basin, California were analyzed. The results indicate that climatic variability exists in all the data types and are partially coincident with known climate cycles such as the Pacific Decadal Oscillation and the El Nino-Southern Oscillation. The time-series also indicate lagged correlations between tree-ring indices, streamflow, stream base flow, and ground-water levels. These correlations and reconstructed time-series can be used to better understand the relation of hydrologic response to climatic forcings and to facilitate the simulation of streamflow and ground-water recharge for a more realistic approach to water-resource management. Published by Elsevier B.V.

Journal of Hydrology↗

USGS2020

RestoreNet: An emerging restoration network reveals controls on seeding success across dryland ecosystems

Drylands are Earth's largest terrestrial biome and support one‐third of the global population. However, they are also highly vulnerable to land degradation. Despite widespread demand for dryland restoration and rehabilitation, little information is available to help land managers effectively re‐establish native perennial vegetation across drylands. RestoreNet is an emerging dryland restoration network that systematically tests revegetation techniques across environmental gradients. Using the RestoreNet experimental framework, we tested the effectiveness of restoration treatments (i.e. ConMod nurse plant structures, mulch, pits) that increase soil moisture and seed mixes with different climatic niches to achieve revegetation goals. Across sites, seedling recruitment was consistently influenced by treatment and seed mix type. Pit and mulch treatments increased total seedling density, with pits promoting the highest seeded species recruitment while limiting non‐native species establishment. Seeding increased total seedling density regardless of seed mix type, but cooler‐adapted seed mixes promoted greater seeded species density and resulted in lower density of unseeded (non‐native) species relative to warmer‐adapted mixes. Seedling recruitment was also controlled by the temporal and environmental context of restoration with the positive effect of high precipitation greatest in the weeks immediately following seeding. Above‐average precipitation during the study period across most of the sites may partially explain why the highest seeded species recruitment occurred in pit treatments and seed mixes with cooler, wetter niche requirements. Synthesis and applications . Results from the dryland restoration network, RestoreNet help to better understand variation in seeding and restoration treatment success across space and time in drylands. Relationships between restoration practices and environmental conditions in our study suggest the importance of anticipatory restoration strategies that forecast seasonal and sub‐seasonal weather conditions and select plant species with climate niche requirements appropriate for current and future climate conditions. This information is critical to land managers tasked with improving ecosystem conditions across degraded dryland regions.

Arizona↗

USGS2021

Tree mortality response to drought-density interactions suggests opportunities to enhance drought resistance

The future of dry forests around the world is uncertain given predictions that rising temperatures and enhanced aridity will increase drought-induced tree mortality. Using forest management and ecological restoration to reduce density and competition for water offers one of the few pathways that forests managers can potentially minimize drought-induced tree mortality. Competition for water during drought leads to elevated tree mortality in dense stands, although the influence of density on heat-induced stress, and the durations of hot or dry conditions that most impact mortality, remain unclear. Understanding how competition interacts with hot-drought stress is essential to recognize how, where, and how much reducing density can help sustain dry forests in a rapidly changing world. Here, we integrated repeat measurements of 28,881 ponderosa pine trees across the western US (2000-2017) with soil moisture estimates from a water balance model to examine how annual mortality responds to competition, temperature and soil moisture conditions. Tree mortality responded most strongly to basal area, and was elevated in places with high mean temperatures, unusually hot 7-year high temperature anomalies, and unusually dry 8-year low soil moisture anomalies. Mortality was also lower in places that experienced unusually wet 3-year soil moisture anomalies between measurements. Importantly, we found that basal area interacts with temperature and soil moisture, exacerbating mortality during times of stress imposed by high temperature or low moisture. Synthesis and Applications: Our results imply that a 50% reduction in forest basal area could reduce drought-driven tree mortality by 20-80%. The largest impacts of density reduction are seen in areas with high current basal area and places that experience high temperatures and/or severe multiyear droughts. These interactions between competition and drought are critical to understand past and future patterns of tree mortality in the context of climate change, and provide information for resource managers seeking to enhance dry forest drought resistance.

Journal of Applied Ecology.↗

USGS2020

Changes in climate and land cover affect seasonal streamflow forecasts in the Rio Grande headwaters

Seasonal streamflow forecast bias, changes in climate, snowpack, and land cover, and the effects of these changes on relations between basin‐wide snowpack, SNOw TELemetry (SNOTEL) station snowpack, and seasonal streamflow were evaluated in the headwaters of the Rio Grande, Colorado. Results indicate that shifts in the seasonality of precipitation and changing climatology are consistent with periods of overprediction and underprediction in streamflow forecasts. Multiple linear regression of SNOTEL data, postcedent precipitation, and land‐cover changes explained 2%–18% more variability in streamflow prediction than using SNOTEL station data alone. Simulated basin‐wide snowpack from a physically based model had significant negative trends in snow water equivalent (−4.33 mm/yr) and snow‐covered area (−0.05%/yr) during the melt period April–June. Simulated streamflow from a precipitation‐runoff model increased an average 5% when the effects of bark beetle‐induced tree mortality were compared to a baseline simulation with static vegetation. The effects of a 2013 wildfire increased simulated seasonal streamflow an average 35% for 1–4 years postfire. The combined effects of climate and land‐cover changes on snowpack‐streamflow relations highlight the difficulty in seasonal streamflow forecasting, which has important implications for water‐resource management.

Colorado↗

USGS2014

The aging of America's reservoirs: In-reservoir and downstream physical changes and habitat implications

Reservoirs are important for various purposes including flood control, water supply, power generation, and recreation. The aging of America's reservoirs and progressive loss of water storage capacity resulting from ongoing sedimentation, coupled with increasing societal needs, will cause the social, economic, environmental, and political importance of reservoirs to continually increase. The short- and medium-term (<50 years) environmental consequences of reservoir construction and operation are well known and include an altered flow regime, lost connectivity (longitudinal, floodplain), an altered sediment regime, substrate compositional change, and downstream channel degradation. In general, reservoir-related changes have had adverse consequences for the natural ecosystem. Longer term (>50 years) environmental changes as reservoirs enter “old” age are less understood. Additional research is needed to help guide the future management of aging reservoir systems and support the difficult decisions that will have to be made. Important research directions include assessment of climate change effects on aging and determination of ecosystem response to ongoing aging and various management actions that may be taken with the intent of minimizing or reversing the physical effects of aging.

Journal of the American Water Resources Associatio↗

USGS2010

Interactions between walleyes and smallmouth bass in a Missouri River reservoir with consideration of the influence of temperature and prey

Walleyes Sander vitreus are the most popular fish among South Dakota anglers, but smallmouth bass Micropterus dolomieu were introduced to provide new angling opportunities. Some walleye anglers have reported reductions in the quality of walleye fisheries since the introduction of smallmouth bass and attribute this to the consumption of young walleyes by smallmouth bass and competition for shared prey resources. We quantified the diets of walleyes and smallmouth bass in the lower reaches of Lake Sharpe (a Missouri River reservoir), calculated the diet overlap between the two predators, and determined whether they partitioned shared prey based on size. We also quantified walleye diets in the upper reach of the reservoir, which has a different prey base and allowed us to compare the growth rates of walleyes within Lake Sharpe. Age-0 gizzard shad Dorosoma cepedianum composed a substantial proportion of the diets of both predators, regardless of location, for most of the growing season; the patterns in shad vulnerability appeared to drive the observed patterns in diet overlap. Smallmouth bass appeared to consume a smaller size range of gizzard shad than did walleyes, which consumed a wide range. Smallmouth bass consumed Sander spp. in some months, but in very low quantities. Given that global climate change is expected to alter the population and community dynamics in Great Plains reservoirs, we also used a bioenergetics approach to predict the potential effects of limiting prey availability (specifically, the absence of gizzard shad and rainbow smelt Osmerus mordax ) and increased water temperatures (as projected from global climate change models) on walleye and smallmouth bass growth. The models indicated that the absence of rainbow smelt from the diets of walleyes in upper Lake Sharpe would reduce growth but that the absence of gizzard shad would have a more marked negative effect on both predators at both locations. The models also indicated that higher water temperatures would have an even greater negative influence on walleye growth; however, smallmouth bass growth was predicted to increase with higher temperatures. Fisheries managers should consider strategies to enhance the prey base or mitigate the effects of increased water temperatures that may occur in the future as a result of global climate change. Such proactive actions may alleviate potential future competition between walleyes and smallmouth bass resulting from changes in the fish community.

North American Journal of Fisheries Management↗

USGS2015

Complex terrain alters temperature and moisture limitations of forest soil respiration across a semiarid to subalpine gradient

Forest soil respiration is a major carbon (C) flux that is characterized by significant variability in space and time. We quantified growing season soil respiration during both a drought year and a nondrought year across a complex landscape to identify how landscape and climate interact to control soil respiration. We asked the following questions: (1) How does soil respiration vary across the catchments due to terrain-induced variability in moisture availability and temperature? (2) Does the relative importance of moisture versus temperature limitation of respiration vary across space and time? And (3) what terrain elements are important for dictating the pattern of soil respiration and its controls? Moisture superseded temperature in explaining watershed respiration patterns, with wetter yet cooler areas higher up and on north facing slopes yielding greater soil respiration than lower and south facing areas. Wetter subalpine forests had reduced moisture limitation in favor of greater seasonal temperature limitation, and the reverse was true for low-elevation semiarid forests. Coincident climate poorly predicted soil respiration in the montane transition zone; however, antecedent precipitation from the prior 10 days provided additional explanatory power. A seasonal trend in respiration remained after accounting for microclimate effects, suggesting that local climate alone may not adequately predict seasonal variability in soil respiration in montane forests. Soil respiration climate controls were more strongly related to topography during the drought year highlighting the importance of landscape complexity in ecosystem response to drought.

Journal of Geophysical Research: Biogeosciences↗

USGS2000

Stratigraphic and structural evolution of the Selenga Delta Accommodation Zone, Lake Baikal Rift, Siberia

Seismic reflection profiles from the Lake Baikal Rift reveal extensive details about the sediment thickness, structural geometry and history of extensional deformation and syn-rift sedimentation in this classic continental rift. The Selenga River is the largest single source of terrigenous input into Lake Baikal, and its large delta sits astride the major accommodation zone between the Central and South basins of the lake. Incorporating one of the world's largest lacustrine deltas, this depositional system is a classic example of the influence of rift basin structural segmentation on a major continental drainage. More than 3700 km of deep basin-scale multi-channel seismic reflection (MCS) data were acquired during the 1989 Russian and the 1992 Russian–American field programs. The seismic data image most of the sedimentary section, including pre-rift basement in several localities. The MCS data reveal that the broad bathymetric saddle between these two major half-graben basins is underlain by a complex of severely deformed basement blocks, and is not simply a consequence of long-term deltaic deposition. Maximum sediment thickness is estimated to be more than 9 km in some areas around the Selenga Delta. Detailed stratigraphic analyses of the Selenga area MCS data suggest that modes of deposition have shifted markedly during the history of the delta. The present mode of gravity- and mass-flow sedimentation that dominates the northern and southern parts of the modern delta, as well as the pronounced bathymetric relief in the area, are relatively recent developments in the history of the Lake Baikal Rift. Several episodes of major delta progradation, each extending far across the modern rift, can be documented in the MCS data. The stratigraphic framework defined by these prograding deltaic sequences can be used to constrain the structural as well as depositional evolution of this part of the Baikal Rift. An age model has been established for this stratigraphy, by tying the delta sequences to the site of the Baikal Drilling Project 1993 Drill Hole. Although the drill hole is only 100 m deep, and the base of the cores is only ∼670 ka in age, ages were extrapolated to deeper stratigraphic intervals using the Reflection-Seismic-Radiocarbon method of Cohen et al. (1993). The deep prograding delta sequences now observed in the MCS data probably formed in response to major fluctuations in sediment supply, rather than in response to shifts in lake level. This stratigraphic framework and age model suggest that the deep delta packages developed at intervals of approximately 400 ka and may have formed as a consequence of climate changes affiliated with the northern hemisphere glaciations. The stratigraphic analysis also suggests that the Selenga Basin and Syncline developed as a distinct depocentre only during the past ∼2–3 Ma.

Lake Baikal Rift↗

USGS1985

Stratigraphic and interregional changes in Pennsylvanian coal-swamp vegetation: Environmental inferences

Quantitative analysis of Pennsylvanian coal-swamp vegetation provides a means of inferring organization and structure of communities. Distribution of these communities further provides inferences about environmental factors, including paleoclimate. Our observations are based on in situ, structurally preserved peat deposits in coal-ball concretions from 32 coal seams in the eastern one-half of the United States and from several seams in western Europe and on spore assemblages from more than 150 seams. There were three times of particularly significant and nearly synchronous vegetational changes in the Midcontinent and Appalachian coal regions during the Pennsylvanian Period. Each was different in kind and magnitude. The first marked changes occurred during the early part of the Middle Pennsylvanian with the fluctuating decline in the high level of lycopod dominance. The abundance of cordaites increased. There was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity. Changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree-fern spores. The next significant time of change was during the middle part of the Middle Pennsylvanian, representing both a culmination of earlier trends and expansions of cordaites in the Midcontinent where there was a maximum change in species without net loss of diversity. Tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the Atokan-Desmoinesian transition of the Midcontinent. The third and sharpest break occurred near the Middle—Late Pennsylvanian boundary when extinctionsof the dominant, coal-swamp lycopods allowed development of tree-fern dominance. The Late Pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the Middle Pennsylvanian swamps. Paralleling the changes in floras through the Pennsylvanian are changes in preservational aspects of the peat. These include a decline in shoot/root ratios from approximately 1 to < 1 during the first time of vegetational changes and a rise in this ratio during the second; there was a parallel rise and fall in fusain abundance and a rise in wood/periderm ratios. The stratigraphic distribution of identified coal resources in the United States is interpreted as largely dependent on net changes in relative wetness of Pennsylvanian coal swamps, a pattern of drying during the first period of vegetational change, followed by a concomitant increase in continuous wet climate with brackish influence in the Midcontinent during the second; this was followed by a time of extreme moisture stress bringing on the third, and most severe, vegetational change.

International Journal of Coal Geology↗

USGS2013

Export of dissolved organic carbon from the Penobscot River basin in north-central Maine

Dissolved organic carbon (DOC) flux from the Penobscot River and its major tributaries in Maine was determined using continuous discharge measurements, discrete water sampling, and the LOADEST regression software. The average daily flux during 2004–2007 was 71 kg C ha −1 yr −1 (392 Mt C d −1 ), an amount larger than measured in most northern temperate and boreal rivers. Distinct seasonal variation was observed in the relation between concentration and discharge (C–Q). During June through December (summer/fall), there was a relatively steep positive C–Q relation where concentration increased by a factor of 2–3 over the approximately 20-fold range of observed stream discharge for the Penobscot River near Eddington, Maine. In contrast, during January through May (winter/spring), DOC concentration did not increase with increasing discharge. In addition, we observed a major shift in the C–Q between 2004–2005 and 2006–2007, apparently resulting from unprecedented rainfall, runoff, and soil flushing beginning in late fall 2005. The relative contribution to the total Penobscot River basin DOC flux from each tributary varied dramatically by season, reflecting the role of large regulated reservoirs in certain basins. DOC concentration and flux per unit watershed area were highest in tributaries containing the largest areas in palustrine wetlands. Tributary DOC concentration and flux was positively correlated to percentage wetland area. Climatic or environmental changes that influence the magnitude or timing of river discharge or the abundance of wetlands will likely affect the export of DOC to the near-coastal ocean.

Maine↗

USGS2020

Isotopic and geochemical assessment of the sensitivity of groundwater resources of Guam, Mariana Islands, to intra- and inter-annual variations in hydroclimate

Assessing the sensitivity of groundwater systems to hydroclimate variability is critical to sustainable management of the water resources of Guam, US territory. We assess spatial and temporal variability of isotopic and geochemical compositions of vadose and phreatic groundwater sampled from cave drip sites and production wells, respectively, to better understand the vulnerability of the freshwater lens on Guam to variability in hydroclimate. We independently evaluate the existing conceptual model of the Northern Guam Lens Aquifer that is largely based on physical, as opposed to geochemical, observations. Sampling was conducted from 2008 to 2015, over which rainfall gradually increased. Major ion geochemistry and Sr isotope values of groundwater show varying influence from soil, limestone bedrock, and seawater. Geochemical modeling that can explain spatial variability in groundwater Na+ and Mg2+ concentrations and Sr/Ca and 87Sr/86 Sr values indicates that groundwater compositions are dominantly controlled by mixing of freshwater with seawater and water-rock interaction. Differences between amount-weighted annual average precipitation δ18 O values and groundwater δ18 O values indicate a recharge bias toward the wet season, consistent with other tropical carbonate island aquifer settings. Intra- and inter-annual variations in Na+ concentrations and δ18 O values in groundwater reflect sensitivity of recharge to seasonal variations in rainfall amount and changes in annual rainfall amounts. Our results indicate the influence of multiple modes of recharge on groundwater compositions and spatial variability in the sensitivity of groundwater to seawater mixing. This sensitivity of the freshwater lens points to the vulnerability of groundwater resources to changes in recharge associated with climate, land-use change, and increases in population.

Journal of Hydrology↗

USGS2022

Demographic and environmental correlates of home ranges and long-distance movements of Mohave ground squirrels

Space use by mammals can differ among age-classes, sexes, or seasons, and these processes are recognized as adaptive behavioral strategies. Semi-fossorial ground squirrels, in particular, have shown age- and sex-specific patterns in their aboveground movement behaviors. We studied space use of Mohave ground squirrels ( Xerospermophilus mohavensis ) at the Freeman Gulch study site in the central region of their range in the Mojave Desert, California. We documented the timing of their full annual cycle, investigated correlates of size of home ranges of adults and distance of long-distance movements by juveniles, and evaluated whether juvenile body masses and movements were related to interannual climatic variation. Adult males emerged from burrows and entered hibernation sooner than did adult females. Home ranges were larger for males ( ⁠ x ¯ "> x ¯ x¯ ± SD = 0.50 ± 0.40 km 2 ) than females (0.05 ± 0.03 km 2 ), especially during the mating season. Maximum distances moved by juveniles did not differ significantly between males (1.6 ± 2.3 km) and females (1.0 ± 1.8 km), and both sexes were equally likely to travel long distances from natal sites. The longest-distance movement we documented was 7.7 km by a juvenile male. Juveniles born in a year of low vegetation productivity gained significantly less mass (97 ± 7 g) and traveled shorter distances than those born in a year of higher vegetation productivity (177 ± 20 g). Our findings were similar to those documented in the Coso Range study site in the northern region of the geographic range of the species, indicating that movement patterns are similar range-wide. Mohave ground squirrels responded strongly to climate variation, and global climate change will likely result in a northward shift in suitable habitats. Informed conservation planning, therefore, will be essential for this rare, declining species.

California↗

USGS2020

The influence of climate variability on the accuracy of NHD perennial and non-perennial stream classifications

National Hydrography Dataset (NHD) stream permanence classifications (SPC; perennial, intermittent, and ephemeral) are widely used for data visualization and applied science, and have implications for resource policy and management. NHD SPC were assigned using a combination of topographic field surveys and interviews with local residents. However, previous studies indicate that non‐NHD, in situ streamflow observations (NNO) frequently disagree with NHD SPC. We hypothesized that differences in annual climate conditions between map creation years and the years NNO were collected contributed to disagreement between NNO and NHD SPC. We compared NHD SPC to 10,055 NNO (classified as “wet” or “dry”) collected in the Pacific Northwest between 1977 and 2015. Annual climate conditions were described with the Palmer Drought Severity Index (PDSI). Stream order was added as a covariate to account for different effects along the stream network. NHD SPC agreed with 80.5% of NNO. “Dry” NNO were five times more likely to disagree with NHD than “wet” NNO ( p < 0.0001). Disagreement was greatest on first‐order streams. When NHD SPC were collected during a wetter period than NNO the probability of disagreement increased by a factor of 1.17 ( p < 0.0001) per unit difference in PDSI. The influence of climate on disagreements between NNO and NHD SPC provides support for the continued development of dynamic models representing SPC as opposed to static NHD classifications.

Journal of the American Water Resources Associatio↗

USGS2014

Small crater modification on Meridiani Planum and implications for erosion rates and climate change on Mars

A morphometric and morphologic catalog of ~100 small craters imaged by the Opportunity rover over the 33.5 km traverse between Eagle and Endeavour craters on Meridiani Planum shows craters in six stages of degradation that range from fresh and blocky to eroded and shallow depressions ringed by planed off rim blocks. The age of each morphologic class from <50–200 ka to ~20 Ma has been determined from the size-frequency distribution of craters in the catalog, the retention age of small craters on Meridiani Planum, and the age of the latest phase of ripple migration. The rate of degradation of the craters has been determined from crater depth, rim height, and ejecta removal over the class age. These rates show a rapid decrease from ~1 m/Myr for craters < 1 Ma to ~ <0.1 m/Myr for craters 10–20 Ma, which can be explained by topographic diffusion with modeled diffusivities of ~10 −6  m 2 /yr. In contrast to these relatively fast, short-term erosion rates, previously estimated average erosion rates on Mars over ~100 Myr and 3 Gyr timescales from the Amazonian and Hesperian are of order < 0.01 m/Myr, which is 3–4 orders of magnitude slower than typical terrestrial rates. Erosion rates during the Middle-Late Noachian averaged over ~250 Myr, and ~700 Myr intervals are around 1 m/Myr, comparable to slow terrestrial erosion rates calculated over similar timescales. This argues for a wet climate before ~3 Ga in which liquid water was the erosional agent, followed by a dry environment dominated by slow eolian erosion.

Journal of Geophysical Research E: Planets↗

USGS2016

An empirical assessment of which inland floods can be managed

Riverine flooding is a significant global issue. Although it is well documented that the influence of landscape structure on floods decreases as flood size increases, studies that define a threshold flood-return period, above which landscape features such as topography, land cover and impoundments can curtail floods, are lacking. Further, the relative influences of natural versus built features on floods is poorly understood. Assumptions about the types of floods that can be managed have considerable implications for the cost-effectiveness of decisions to invest in transforming land cover (e.g., reforestation) and in constructing structures (e.g., storm-water ponds) to control floods. This study defines parameters of floods for which changes in landscape structure can have an impact. We compare nine flood-return periods across 31 watersheds with widely varying topography and land cover in the southeastern United States, using long-term hydrologic records (≥20 years). We also assess the effects of built flow-regulating features (best management practices and artificial water bodies) on selected flood metrics across urban watersheds. We show that landscape features affect magnitude and duration of only those floods with return periods ≤10 years, which suggests that larger floods cannot be managed effectively by manipulating landscape structure. Overall, urban watersheds exhibited larger (270 m 3 /s) but quicker (0.41 days) floods than non-urban watersheds (50 m 3 /s and 1.5 days). However, urban watersheds with more flow-regulating features had lower flood magnitudes (154 m 3 /s), but similar flood durations (0.55 days), compared to urban watersheds with fewer flow-regulating features (360 m 3 /s and 0.23 days). Our analysis provides insight into the magnitude, duration and count of floods that can be curtailed by landscape structure and its management. Our findings are relevant to other areas with similar climate, topography, and land use, and can help ensure that investments in flood management are made wisely after considering the limitations of landscape features to regulate floods.

Journal of Environmental Management↗

USGS2015

Groundwater recharge assessment at local and episodic scale in a soil mantled perched karst aquifer in southern Italy

Groundwater recharge assessment of karst aquifers, at various spatial and temporal scales, is a major scientific topic of current importance, since these aquifers play an essential role for both socio-economic development and fluvial ecosystems. In this study, groundwater recharge was estimated at local and episodic scales in a representative perched karst aquifer in a region of southern Italy with a Mediterranean climate. The research utilized measurements of precipitation, air temperature, soil water content, and water-table depth, obtained in 2008 at the Acqua della Madonna test area (Terminio Mount karst aquifer, Campania region). At this location the aquifer is overlain by ash-fall pyroclastic soils. The Episodic Master Recession (EMR) method, an improved version of the Water Table Fluctuation (WTF) method, was applied to estimate the amount of recharge generated episodically by individual rainfall events. The method also quantifies the amount of precipitation generating each recharge episode, thus permitting calculation of the Recharge to the Precipitation Ratio (RPR) on a storm-by-storm basis. Depending on the seasonally varying air temperature, evapotranspiration, and precipitation patterns, calculated values of RPR varied between 35% and 97% among the individual episodes. A multiple linear correlation of the RPR with both the average intensity of recharging rainfall events and the antecedent soil water content was calculated. Given the relatively easy measurability of precipitation and soil water content, such an empirical model would have great hydrogeological and practical utility. It would facilitate short-term forecasting of recharge in karst aquifers of the Mediterranean region and other aquifers with similar hydrogeological characteristics. By establishing relationships between the RPR and climate-dependent variables such as average storm intensity, it would facilitate prediction of climate-change effects on groundwater recharge. The EMR methodology could further be applied to other aquifers for evaluating the relationship of recharge to various hydrometeorological and hydrogeological processes.

Journal of Hydrology↗

USGS2023

Modeling groundwater-level responses to multiple stresses using transfer-function models and wavelet analysis in a coastal aquifer system

In coastal aquifers, dynamic stresses such as climate forcings, groundwater withdrawals, and ocean tidal fluctuations cause nonlinear responses to groundwater levels. Such responses to the stresses impact groundwater resources and related flooding and infrastructure risks at multiple scales. We used time-series models such as transfer-function models and wavelet analysis to quantify the relative contribution of these stresses to groundwater-level fluctuation in wells from the unconfined and confined aquifers in an Atlantic coastal aquifer. Climate forcings, such as precipitation and temperature, explained most of the groundwater-level variation for wells in the unconfined aquifer, whereas groundwater withdrawals were the dominant driver of groundwater levels for wells in the confined aquifer. The impact of groundwater withdrawals also was detected in several wells in the unconfined aquifer. Although the influence of ocean tides on groundwater levels commonly is observed in coastal aquifers, we found that daily groundwater withdrawals can obscure the semi-diurnal coherence signal of the two series. The magnitude of groundwater-level fluctuation that could be explained solely by tides was minor compared to that explained by climate or withdrawal stresses. Transfer-function modeling showed seasonal withdrawals from wells in confined aquifers had a significant, yet heterogeneous influence on groundwater levels in coastal aquifers, which highlights climate and withdrawals as key compounding stresses in coastal hydrology. This study demonstrates the value of time-series approaches to advance characterization of groundwater systems in areas with limited hydrogeologic parameter information.

Virginia↗

USGS2024

Evaluating seawater intrusion forecast uncertainty under climate change in the Pajaro Valley, California

Climate change and climate variability impacts such as rising sea levels have the potential to exacerbate seawater intrusion and the strain on coastal freshwater resources in already stressed groundwater basins such as those in the Pajaro Valley groundwater basin, California. Regional hydrologic models are often coupled with climate projections to forecast future hydrologic conditions and inform adaptive resources management strategies. However, there is high uncertainty in the future projections of water resources due to uncertainties from downscaling global general circulation models (GCMs) to local scale climate change projections, future land use changes, and the inherent uncertainty of developed hydrologic models. Future climate projections and the magnitude of their influence on modeled hydrologic drivers are highly variable. Therefore, to develop a forecast model, an ensemble of different projections can be used to capture a wider range of basin responses and the associated uncertainties in the modeled forecasts. Understanding the reliability and uncertainty of forecasts is important for developing climate adaptation strategies such as developing protective thresholds, particularly at the basin scale where the impacts are felt, and adaptation is implemented. To demonstrate this, an uncertainty analysis of groundwater level and seawater intrusion forecasts for the Pajaro Valley groundwater basin was performed using an ensemble of three future climate projections with the Pajaro Valley Integrated Hydrologic Model (PVIHM) and the first-order second moment (FOSM) method. FOSM uncertainty analysis of hydrologic forecasts across a multi-GCM climate ensemble provides an upper and lower bound of potential impacts of climate change on sustainability targets related to mitigating seawater intrusion. The groundwater level forecasts’ narrow range of variability can help policymakers in adaptation planning by constraining possible outcomes to a focused range for risk-management decisions. However, less than one-third of groundwater level forecasts met the current protection thresholds to prevent chronic lowering of groundwater. Therefore, sustainability targets may need to be reassessed. Relative to groundwater level changes, the seawater intrusion forecasts had larger uncertainty due to the GCM climate projections and the simulated hydrologic response that were compounded by the propagation of scaling and bias from the GCMs and model simplifications in simulating the coastal boundary.

California↗