Average Precipitation Conditions Research Articles

Influence of fine-scale habitat characteristics on sage-grouse nest site selection and nest survival varies by mesic and xeric site conditions

AbstractResource managers and scientists across western U.S. agencies seek methodologies for identifying environmental attributes important to both wildlife conservation and broad-scale land stewardship. The Greater Sage-Grouse (Centrocercus urophasianus; hereafter, sage-grouse) exemplifies a species in need of this broad-scale approach given widespread population declines that have resulted from loss and degradation of habitat from natural and anthropogenic disturbances. These include agricultural land conversion, conifer expansion, energy development, and wildfire coupled with ecological conversion by invasive plants such as cheatgrass (Bromus tectorum). Development of habitat assessments and conservation actions for sage-grouse benefit from studies that link demographic responses to habitat selection patterns. To address this, we examined nest survival of sage-grouse in relation to fine-scale habitat patterns (i.e., field-based habitat measurements) that influenced nest site selection, using data from nests of telemetered females at 17 sites over 6 years in Nevada and northeastern California, USA. Importantly, sites spanned mesic and xeric average precipitation conditions that contributed substantially to vegetation community structure across cold desert ecosystems of the North American Great Basin. Vegetative cover immediately surrounding sage-grouse nests was important for both nest site selection and nest survival, but responses varied between mesic and xeric sites. For example, while taller perennial grasses were selected at xeric sites, we found no evidence of selection for perennial grass at mesic sites, indicating a functional response to availability of habitat features between hydrographic regions. Furthermore, perennial grass height and forb height both had positive effects on nest survival at xeric sites, but we found varying effects at mesic sites. We emphasize that precipitation conditions driving ecosystem productivity vary regionally among sagebrush communities, shaping vegetation structure and suitable habitat conditions for nesting sage-grouse.

Impact of climate change on the elevational and latitudinal distributions of populations of Tipulidae (Diptera) in Wales, United Kingdom

Abstract As dominant features of most ecosystems, insects are responsive to changes in climate, both over short temporal scales (e.g. seasonal fluctuations in abundance) and over longer evolutionary scales (e.g. decade-scale changes in patterns of biodiversity). One such taxonomic group that is sensitive to changing climate are the craneflies (Diptera: Tipulidae). Here, we used aggregated biodiversity data to examine elevational and latitudinal distributions of adult Tipulidae between 1976 and 2019 in Wales, UK, and we related these distributions to climatic patterns. Our analyses showed that species with earlier-emerging adults were most affected by weather conditions in the year before observation. Specifically, as temperature increased, observed elevation increased in high-precipitation conditions, remained stable in average-precipitation conditions and decreased in low-precipitation conditions. For species with later-emerging adults, associations were seen between elevation and weather conditions in the year of observation. Observed latitude generally exhibited a negative association with maximum temperature in the year before observation, with observations of Tipulidae trending southwards during the 43-year study period. Our results support consideration of emergence phenology, weather and habitat data when predicting species distributional changes attributable to climate change, which is vital in understanding the selection pressures that species face in a changing environment.

Intermittency as an indicator of drought in streamflow and groundwater

AbstractUnder normal precipitation conditions, increasing water demand causes groundwater level to deplete and streamflow to decrease. This results in more frequent intermittency. The so‐called intermittency cycle hypothesis is examined in this study. It is a vicious circle in hydrology making both surface and groundwater resources less efficient in supplying ever‐increasing water demand. To test the hypothesis, a data‐based analysis is applied to Gediz, Kucuk Menderes, and Ergene river basins in western Turkey. Results at basin‐ and station‐scale show no change in precipitation while streamflow fluctuates with a tendency to decrease and groundwater steeply declines. Groundwater is used excessively to meet the drastically increased water demand. With the overuse of groundwater, water table descends, streamflow decreases and intermittency increases. Intermittency ratio of a river is found related to the decrease in streamflow and the drop in groundwater level. It can trigger drought in streamflow and groundwater. It is concluded that intermittency can be taken as a quantitative indicator of drought in streamflow and groundwater.

Spatiotemporal Variations in the Intensity of Human Activity in Inner Mongolia and the Identification of Influencing Forces

The quantitative evaluation of the intensity of regional human activity can reflect changes in the relationship between people and the environment and provide a scientific basis for the formulation of land-use policy and for the construction of the ecological environment. This paper adopted the ratio of the area of construction land to the total area to calculate human activity intensity in Inner Mongolia at the league/city, banner/county, and pixel levels, respectively. On this basis, the overall change in human activity intensity and its spatiotemporal differentiation, geographical unit change, and spatial autocorrelation were analyzed. The results are as follows: (1) The intensity of human activity increased from 2000 to 2020. The intensity of human activity in Inner Mongolia was 8.71% in 2000, and it increased to 8.73% in 2010 and to 9.71% in 2020. The growth rate has accelerated since 2010. (2) The areas with high and medium intensity of human activities are mainly concentrated in the area south of the Hinggan–Yinshan–Helan Mountains. The intensity in the Hulunbeier grassland area and Alxa desert area is relatively low, and the diffusion effect gradually becomes prominent in the proximal local area. (3) The results for the detection of influencing factors indicate that the livestock density, multi-year average precipitation conditions, and population density have significant driving effects on the changes in intensity of human activity in Inner Mongolia.

Hydro-geomorphological characterization of the Rio Grande Basin, Brazil, using geospatial approach

Several studies have presented morphometric analysis as the key to understanding hydrological behavior or support tool for the assessment of natural resources and environmental risks in a river basin. The Rio Grande Basin has great socioeconomic and environmental relevance for Brazil; however, its morphometric characterization is not widely known. Therefore, we present the morphometric characteristics of the Rio Grande Basin (BHRG), from the geometric, relief, and drainage variables. Data processing was carried out using the Geographic Information System (GIS), from the Digital Elevation Model (DEM). The results indicate that the BHRG is of the fifth order, presenting a dendritic drainage pattern, low susceptibility to flooding under normal precipitation conditions, sinuous watercourses, and an undulating relief. In addition, the BHRG is permeable, poorly drained, and displays low capacity to generate and maintain drainage tracts. The findings can contribute to a better understanding of hydrological behavior on a river basin and support integrated water resource plans.

Morphometric characterization of Mestre Campo Stream Watershed, in Piranga City, Minas Gerais

The multiple environmental dynamics of watersheds make these natural spaces interesting objects of study, and in areas with few scientific investigations, such as the Mestre Campo Stream watershed, the need for these investigations is even greater. The accomplishment of this paper sought to characterize the morphometry of Mestre Campo Stream Watershed, located in Piranga City, Minas Gerais, Brazil, as a first activity to create a management plan for the natural resources available in the area. Therefore, TOPODATA geomorphological data were used in a geographic information system (GIS) to extract the morphometric information – area and respective perimeter, length of axis and of drainage network – from the study area and, then, these variables were used to estimate the following indicators: form factor, circularity and compactness indexes, elongation ratio and drainage density, in order to describe the watershed. The morphometric indexes indicated an elongated behavior for the watershed, characterizing it as a space of low susceptibility to flooding under normal precipitation conditions. In addition, the drainage network showed fourth-order ramifications and a median capacity of drainage. The sub-watersheds that makes the Mestre Campo Stream Watershed were also characterized, the Sub-watershed of Brum Stream presented a rounded shape, while the Alto Mestre Campo Sub-watershed presented elongated characteristics. These results highlight the heterogeneity of Mestre Campo Stream Watershed, which must be considered when elaborating the management plan for the studied watershed, respecting the particularities of that geographic space in order to properly explore its natural resources.

Morphometric analysis of an Areal Watershed in Taubaté, SP, Brazil

In 1991, the Integrated Water Resources Management System (SIGRHI) in the State of São Paulo adopted the watershed as a territorial unit for studies, integrated planning and sustainable development. The morphometric analysis of small watersheds, which involves the characterization of geometric parameters, relief, drainage network, combined with land use and occupation, may constitute an important model for environmental analysis of larger watersheds. This study aimed at characterization of the morphometry in the Areal river basin, in the city of Taubaté, São Paulo. The study found 1.89 km² of area, 7.44 km of perimeter and 3.11 km in length of the basin axis, which allowed the calculation of the compactness coefficient (Kc = 1.51), form factor, (F = 0.195) and circularity index (CI = 0.43), indicating that under normal precipitation conditions, this basin is unlikely to be flooded, due to the distance from the unit, leading to smaller concentrate outflow. The results obtained for the Maintenance Coefficient (Cm) indicate that 260 m² is required to maintain each meter of perennial channel. The high values of drainage density (Dd = 3.35 km.km-2) and sinuosity index (Is = 0.95) indicate that drainage channels in the area are rectilinear, thus suggesting the occurrence of a high surface runoff associated with high dissection. The analysis of land use and occupation revealed that, from the seven types of vegetation cover, the dominant cover in the Areal basin is 0.756 km2 (40%) constituted of pasture, while forest represents 0.580 km2 (31%), 0.321 km2 (17%) of the land cover is constituted of degraded forest. In terms of conservation, the Areal basin is conserved because, besides being located in the environmental preservation area of the Una River Basin, it is located at the meeting of two ecological corridors and is occupied by only 8 families of rural producers. On the other hand, the creation of approximately 120 head of cattle in the upper part of the basin and the existence of gully erosion of the order of 0.018 km2 (1%) of the basin area, which led to increased runoff and sediment concentration in the flat areas marginal to the creek of Areal. Based on morphometric analysis, it was concluded that: Areal watershed presents high capacity to form new watercourses and their relief characteristics, with low sinuosity channels and high values of altimetric amplitude, channel gradient, and density. Drainage, allied to the existence of erosive processes, favors sediment flow and transport. Conservation actions are required to control erosion.

Accounting for dynamics of mean precipitation in drought projections: A case study of Brazil for the 2050 and 2070 periods

Changes in drought around the globe are among the most daunting potential effects of climate change. However, changes in droughts are often not well distinguished from changes in aridity levels. As drought constitutes conditions of aridity, the projected declines in mean precipitation tend to override changes in drought. This results in projections of more dire changes in drought than ever. The overestimate of changes can be attributed to the use of ‘static’ normal precipitation in the derivation of drought events. The failure in distinguishing drought from aridity is a conceptual problem of concern, particularly to drought policymakers. Given that the key objective of drought policies is to determine drought conditions, which are rare and so protracted that they are beyond the scope of normal risk management, for interventions. The main objective of this Case Study of Brazil is to demonstrate the differences between projections of changes in drought based on ‘static’ and ‘30-year dynamic’ precipitation normal conditions. First we demonstrate that the ‘static’ based projections suggest 4-fold changes in the probability of drought-year occurrences against changes by the dynamic normal precipitation. The ‘static-normal mean precipitation’ based projections tend to be monotonically increasing in magnitude, and were arguably considered unrealistic. Based on the ‘30-year dynamic’ normal precipitation conditions, the 13-member GCM ensemble median projection estimates of changes for 2050 under rcp4.511rcp4.5: pathway of greenhouse gas emissions where total radiative forcing is stabilised (at 4.5Wm−2) shortly after 2100, without overshooting the long-run radiative forcing target level. and rcp8.522rcp8.5: pathway of greenhouse gas emissions which, assumes high population and slow income growth with modest rates of technological change and energy intensity improvements, leading to high energy demand and greenhouse gases emissions in absence of climate change policies. suggest: (i) Significant differences between changes associated with rcp4.5 and rcp8.5, and are more noticeable for droughts at long than short timescales in the 2070; (ii) Overall, the results demonstrate more realistic projections of changes in drought characteristics over Brazil than previous projections based on ‘static’ normal precipitation conditions. However, the uncertainty of response of droughts to climate change in CMIP5 simulations is still large, regardless of GCMs selection and translation processes undertaken.

Drivers of Potential Recharge from Irrigated Agroecosystems in the Wisconsin Central Sands

Core Ideas Groundwater in humid regions should be managed for services, not depletion. Climate variability can be a greater driver of potential recharge than crop type. Soil texture can be a significant driver of point‐based potential recharge estimates. Crop phenology may not be predictive of point‐based potential recharge estimates. The expansion of irrigated agriculture on landscapes underlain by coarse‐grained, glacial aquifers in Wisconsin, Minnesota, and Michigan changes the timing and magnitude of groundwater recharge. Water managers require improved estimates of groundwater recharge to manage pumping impacts on groundwater‐fed streams, lakes, and wetlands. We implemented a network of 25 passive capillary lysimeters to infer potential groundwater recharge and evapotranspiration (ET) from irrigated potato (Solanum tuberosum L.), sweet corn and field corn (Zea mays L.), and pea (Pisum sativum L.)–pearl millet [Pennisetum glaucum (L.) R. Br.] rotations in the Wisconsin Central Sands (WCS) from June through November of 2013 to 2016. We found that interannual climate variability, subtle differences in soil texture, and cropping system type drove potential recharge to varying degrees during the summer and fall seasons. Relatively finer soil texture was positively correlated to point estimates of potential recharge. This correlation was the strongest following large precipitation events. June to November cumulative potential recharge for 2013 to 2016 averaged 71 ± 235 mm across all lysimeters. Our findings suggest that aquifer depletion will be an episodic process that leaves surface waters most vulnerable to pumping and recharge impacts during and following drier years in the WCS. Differences among cropping systems were most pronounced under average precipitation conditions, which facilitated potential groundwater losses under field corn and pea–pearl millet rotations and potential groundwater gains under potato rotations. We conclude that regional water management strategies could be effective in buffering against the interannual climate variability of recharge, while localized management strategies could increase irrigation efficiency by targeting crop and soil textural drivers.

The tortoise and the hare: reducing resource availability shifts competitive balance between plant species

Summary Determining how changes in abiotic conditions influence community interactions is a fundamental challenge in ecology. Meeting this challenge is increasingly imperative in the Anthropocene where climate change and exotic species introductions alter abiotic context and biotic composition to reshuffle natural systems. We created plant assemblages consisting of monocultures or equal abundance of the native community dominant bluebunch wheatgrass (Pseudoroegneria spicata) and the exotic spotted knapweed (Centaurea stoebe), a co‐occurring invasive forb that has overtaken grasslands across the western United States. We subjected these composition treatments to drought (20% of average precipitation vs. average) and herbivory on C. stoebe by its biocontrol agent Cyphocleonus achates to explore how reduced precipitation might influence the effects of competition and biocontrol herbivory on C. stoebe's abundance. At the end of 7 years, C. stoebe dominated mixed‐species plots under normal precipitation conditions, with biomass 50% greater than that of the native P. spicata. However, under drought stress, P. spicata's biomass was >200% greater than C. stoebe's. Interestingly, both species were impervious to drought in monoculture, indicating the importance of the drought by competition interaction. The biocontrol herbivore reduced C. stoebe abundance and indirectly increased P. spicata biomass in mixed‐species drought plots, but these effects were only marginally significant and relatively weak. Overall, C. stoebe abundance was primarily driven by the drought by competition interaction, with negatively additive but weak effects of the drought by herbivory interaction. The response of the exotic to the treatments was driven by rapid changes in population density linked to its fast life‐history strategy, while the native's response was driven by changes in per capita plant biomass linked to its slower life‐history strategy. Individual plant performance metrics did not predict overall population responses for the invader, indicating the importance of longer term population measures. Synthesis. These results demonstrate that reduced precipitation inputs linked to climate change can dramatically shift the balance of plant competition, even toggling the advantage from exotic to native dominance. They also illustrate the importance of biotic interactions in predicting species responses to abiotic change.

Measuring Autogenic Recharge over a Karst Aquifer Utilizing Eddy Covariance Evapotranspiration

Autogenic, or direct aquifer recharge can best be measured as the remainder of a water balance utilizing precise measurement of precipitation, evapotranspiration (ET) and runoff. ET is the largest component of a precipitation water balance and can be measured within 5% using an eddy covariance system with Bowen-ratio energy balance corrections. Water balance components of precipitation, evapotranspiration, internal runoff, soil moisture were measured using a eddy covariance system, tipping bucket and visual rain gauges, flumes, and soil-moisture sensors. The research site was located within a 0.19-km2 (46-acre) internal drainage sinkhole basin where runoff never flows beyond the basin, but potentially reaches a cave serving as a drain to the sinkhole. Other than the cave drain, the basin slopes are indistinguishable from other slopes across the Barton Springs Segment of the Edwards Aquifer. Over a 505-day water balance interval where change in soil moisture was negligible and precipitation was 42% above average, ET was 68% of precipitation, discrete internal runoff was 6%, and remaining component of diffuse autogenic recharge was measured as the residual of total rainfall as 26% of rainfall. Over a longer period of average rainfall, internal runoff diminished to 3%, but was as high as 42% of precipitation during single storms when the soils were near saturation. These results closely match results from a five-year water balance over the Trinity Aquifer of Central Texas where ET was measured to be 65% of precipitation using a Bowen-ratio climate tower, runoff was measured to be 5% of precipitation, and recharge was calculated as the residual at 30% of rainfall. ET flux tower data from other sites across Central Texas indicate that under average precipitation conditions, autogenic recharge is about 28% and intervening recharge area runoff is about 3% of precipitation. During years of higher than average precipitation, authogenic recharge and intervening recharge area runoff combined increase within the range of 30% to 45% of precipitation.

Large-scale synoptic types and their impact on European precipitation

Atmospheric circulation strongly modulates precipitation patterns throughout Europe. A selection of synoptic types was chosen to investigate the impact of circulation on the spatial distribution of precipitation within Europe and neighbouring regions (for 1951–2010). Applied were (1) the original and one automated version of the Grosswetterlagen classification, (2) the Vangengeim–Girs classification and (3) a dataset of the North Atlantic Oscillation (NAO). Daily values of the E-OBS gridded precipitation dataset were allocated to synoptic types, visualising precipitation anomalies (in percent) during winter (October–March) and summer (April–September) half years. Anomalies from average precipitation conditions (only) contain days connected to each of the investigated synoptic types. Distinct anomaly patterns become visible and are explained by the location of pressure systems. Patterns are spatially similar between both half years for Grosswetterlagen and Vangengeim–Girs classifications, while the NAO shows pronounced seasonal changes. Precipitation anomaly maps were applied to help explain observed changes in European precipitation amounts from 1981 to 2010, as compared to 1951–1980. Changes of precipitation amounts were related to frequency changes of synoptic types, predominantly during the winter half year. Here, increasing (decreasing) frequencies of synoptic types connected to westerly (easterly) inflow supported higher precipitation amounts in northern Europe and lower amounts in southern Europe.

Rough evaluation of the water-inflow discharge in abandoned mining tunnels using a simplified water balance model: the case of the Cogne iron mine (Aosta Valley, NW Italy)

One of the most complex hydrogeological problems in the design and maintenance of drainage systems in abandoned mining sites is quantifying the maximum water infiltration and, therefore, the amount that is potentially drainable by the tunnels. This problem is compounded when water-inflow data are limited or lacking. The aim of the study was to present a single but reliable model for making this evaluation; this model was applied to the case history of the abandoned Cogne iron ore mining complex (Western Alps, Aosta Valley Region, NW Italy). The study focused on quantifying the amount of water infiltrating into the mine drifts, using a water balance model in a Geographic Information System (GIS) environment. In the model, five different infiltration scenarios were calculated, including a detailed analysis of rainfall data, snow density and thickness (Snow Water Equivalent calculation), and melting periods. The maximum water discharge that could affect the mine tunnels was, therefore, determined under several scenarios of normal precipitation conditions and during heavy rainfall, including the case of the Cogne valley flood in October 2000, used as a reference for the limit conditions. Taking into account the various approximations considered, the results can be considered a good indication of the magnitude of the total amount of water that should be drained out through abandoned mine drifts and in the drainage network during implementation of final closure of the mine.

Objective Optimization of Weather Radar Networks for Low-Level Coverage Using a Genetic Algorithm

Abstract The current Weather Surveillance Radar-1988 Doppler (WSR-88D) radar network is approaching 20 years of age, leading researchers to begin exploring new opportunities for a next-generation network in the United States. With a vast list of requirements for a new weather radar network, research has provided various approaches to the design and fabrication of such a network. Additionally, new weather radar networks in other countries, as well as networks on smaller scales, must balance a large number of variables in order to operate in the most effective way possible. To offer network designers an objective analysis tool for such decisions, a coverage optimization technique, utilizing a genetic algorithm with a focus on low-level coverage, is presented. Optimization is achieved using a variety of variables and methods, including the use of climatology, population density, and attenuation due to average precipitation conditions. A method to account for terrain blockage in mountainous regions is also presented. Various combinations of multifrequency radar networks are explored, and results are presented in the form of a coverage-based cost–benefit analysis, with considerations for total network lifetime cost.

Comparison of Liquid Swine Manure and Aqua-Ammonia Nitrogen Application Timing on Subsurface Drainage Water Quality in Iowa

In Iowa and many other Midwestern states, excess water is removed artificially through subsurface drainage systems. While these drainage systems are vital for crop production, nitrogen (N), added as manure or commercial fertilizer, or derived from soil organic matter, can be carried as nitrate-nitrogen (NO3-N) to downstream water bodies. A five-year, five-replication, field study was initiated in the fall of 1999 in Pocahontas County, Iowa, on 0.05 ha plots that are predominantly Nicollet, Webster, and Canisteo clay loams with 3% to 5% organic matter located on glacial till within the Des Moines Lobe. The objective was to determine the influence of seasonal N application as ammonia or liquid swine manure on flow-weighted NO3-N concentrations and losses in subsurface drainage water and crop yields in a corn-soybean rotation. Four aqua-ammonia N treatments (168 or 252 kg N ha-1 applied for corn in late fall or as an early season side-dress) and three manure treatments (218 kg N ha-1 for corn in late fall or spring or 168 kg N ha-1 in the fall for both corn and soybean) were imposed on subsurface-drained, continuous flow-monitored plots. Precipitation during the drainage season (March to November) was slightly below the long-term norm (722 mm) for all four years in the study period and ranged from 615 mm in 2001 (85% of normal) to 707 mm (98% of normal) in 2004. Monthly rainfall was highly variable, and subsurface drainage, or the lack thereof, usually mimicked the precipitation patterns. On average, 69% of subsurface drainage occurred in May and June of each year, with lower amounts in April and July. Four-year average flow-weighted NO3-N concentrations measured in drainage water were ranked: spring aqua-ammonia 252 (23 mg L-1) = fall manure 168 every year (23 mg L-1) > fall aqua-ammonia 252 (19 mg L-1) = spring manure 218 (18 mg L-1) = fall manure 218 (17 mg L-1) > spring aqua-ammonia 168 (15 mg L-1) = fall aqua-ammonia 168 (14 mg L-1). Corn yields were significantly greater (p = 0.05) for the spring and fall manure 218 rates than for non-manure treatments. Soybean yields were significantly greater (p = 0.05) for the treatments with a spring nitrogen application to the previous corn crop. Overall, under the slightly dry to normal precipitation conditions of this study, corn yields and NO3-N concentrations in subsurface drainage were not significantly different (p = 0.05) between fall and spring treatments at the 168 aqua-ammonia or 218 kg ha-1 N manure N rates.

Effects of increased soil water availability on grassland ecosystem carbon dioxide fluxes

There is considerable interest in how ecosystems will respond to changes in precipitation. Alterations in rain and snowfall are expected to influence the spatio-temporal patterns of plant and soil processes that are controlled by soil moisture, and potentially, the amount of carbon (C) exchanged between the atmosphere and ecosystems. Because grasslands cover over one third of the terrestrial landscape, understanding controls on grassland C processes will be important to forecast how changes in precipitation regimes will influence the global C cycle. In this study we examined how irrigation affects carbon dioxide (CO2) fluxes in five widely variable grasslands of Yellowstone National Park during a year of approximately average growing season precipitation. We irrigated plots every 2 weeks with 25% of the monthly 30-year average of precipitation resulting in plots receiving approximately 150% of the usual growing season water in the form of rain and supplemented irrigation. Ecosystem CO2 fluxes were measured with a closed chamber-system once a month from May-September on irrigated and unirrigated plots in each grassland. Soil moisture was closely associated with CO2 fluxes and shoot biomass, and was between 1.6% and 11.5% higher at the irrigated plots (values from wettest to driest grassland) during times of measurements. When examining the effect of irrigation throughout the growing season (May–September) across sites, we found that water additions increased ecosystem CO2 fluxes at the two driest and the wettest sites, suggesting that these sites were water-limited during the climatically average precipitation conditions of the 2005 growing season. In contrast, no consistent responses to irrigation were detected at the two sites with intermediate soil moisture. Thus, the ecosystem CO2 fluxes at those sites were not water-limited, when considering their responses to supplemental water throughout the whole season. In contrast, when we explored how the effect of irrigation varied temporally, we found that irrigation increased ecosystem CO2 fluxes at all the sites late in the growing season (September). The spatial differences in the response of ecosystem CO2 fluxes to irrigation likely can be explained by site specific differences in soil and vegetation properties. The temporal effects likely were due to delayed plant senescence that promoted plant and soil activity later into the year. Our results suggest that in Yellowstone National Park, above-normal amounts of soil moisture will only stimulate CO2 fluxes across a portion of the ecosystem. Thus, depending on the topographic location, grassland CO2 fluxes can be water-limited or not. Such information is important to accurately predict how changes in precipitation/soil moisture will affect CO2 dynamics and how they may feed back to the global C cycle.

Multiple‐Year Water Balance of Soil Covers in a Semiarid Setting

Surface covers are used to isolate contaminants in hazardous and low-level radioactive sites for time frames ranging from hundreds of years to millennia or more. In the absence of data for such durations, the long-term performance of surface barriers can only be represented with short-term tests or inferred from analogs and modeling. This paper provides evidence of field performance of soil covers for periods up to 17 yr. The results of lysimeter studies from a semiarid site in Washington State show that a cover design known as the Hanford Barrier, which consists of 1.5 m of silt loam above a sand-gravel capillary break, can nearly eliminate drainage. The results were similar if plants were present or not, demonstrating the robustness of the design. Furthermore, reducing the silt loam thickness to 1.0 m (as might occur via erosion), with or without plants, did not lead to drainage. When irrigated to mimic 3x average precipitation conditions, the vegetated Hanford Barrier continued to prevent drainage. Overall, the results showed no loss in performance during the 17 yr of testing. Only when plants were eliminated completely from the 3x precipitation test did drainage occur (rates ranged from 6 to 16 mm yr(-1)). In a separate test, replacing the top 0.2 m of silt loam with dune sand and reducing the plant cover did not lead immediately to the onset of drainage, but soil matric heads within the silt loam noticeably increased. This observation suggests that dune sand migration onto a surface cover has the potential to reduce a cover's ability to minimize deep drainage.

Ground Water Storage Effect on Streamflow for a Southeastern Coastal Plain Watershed

AbstractGround water is known to substantially affect streamflow in regions where the two are interconnected. Likewise, streamflow can rapidly recharge surficial aquifers. Because of this interaction, accurate predictions of streamflow require accurate data on the relationships between streamflow and shallow aquifer conditions. Ground water levels in the surficial aquifer and streamflow were examined for a six‐year period for two small watersheds in south‐central Georgia within the Coastal Plain Physiographic region of the United States. Precipitation for the six‐year period was below average. The shallow water table was elevated during average precipitation conditions, but receded as precipitation decreased. During the three‐year period from 2000 through 2002, the riparian buffer was fully saturated approximately 40% of the time. Lower available aquifer storage was observed for late winter and early spring due to higher rainfall and lower evapotranspiration (ET). During recharge periods, which generally coincided with the period from December to March, the ground water gradient from the upland to the stream was approximately equal to the 3% land surface slope. During other times of the year, the gradient fluctuated dramatically as a response to individual precipitation events, streamflow, and focused recharge. Based on ground water discharging to the stream for 40% of the year, ground water discharge accounted for approximately 4% of the annual precipitation for the period from 2000 through 2002. Aquifer saturation, the fraction of the available aquifer storage filled by ground water, was found to have a substantial effect upon streamflow. During periods when the aquifer was fully saturated, observed storm‐generated streamflow peak rates were greater and of shorter duration. Comparison of similar magnitude events occurring in 1998 indicated that peak discharge was up to three times greater under saturated aquifer conditions than under nonsaturated conditions. Watersheds with substantial pond acreage appear to extend storm‐flow over longer durations. These data indicate the impact of aquifer and pond storage on peak and total discharge in coastal plain watersheds.

PRIESTLEY‐TAYLOR ALPHA COEFFICIENT: VARIABILITY AND RELATIONSHIP TO NDVI IN ARCTIC TUNDRA LANDSCAPES1

ABSTRACT: Average daily values of the Priestley‐Taylor coefficient (a) were calculated for two eddy covariance (flux) tower sites with contrasting vegetation, soil moisture, and temperature characteristics on the North Slope of Alaska over the 1994 and 1995 growing seasons. Because variations in a have been shown to be associated with changes in vegetation, soil moisture, and meteorological conditions in Arctic ecosystems, we hypothesized that a values would be significantly different between sites. Since variations in the normalized difference vegetation index (NDVI) follow patterns of vegetation community composition and state that are largely controlled by moisture and temperature gradients on the North Slope of Alaska, we hypothesized that temporal variations in a respond to these same conditions and thus co‐vary with NDVI. Significant differences in a values were found between the two sites in 1994 under average precipitation conditions. However, in 1995, when precipitation conditions were above average, no significant difference was found. Overall, the variations in a over the two growing seasons showed little relationship to the seasonal progression of the regional NDVI. The only significant relationship was found at the drier, upland study site.

Seasonally in ENSO‐related precipitation, river discharges, soil moisture, and vegetation index in Colombia

An analysis of hydrologic variability in Colombia shows different seasonal effects associated with El Niño/Southern Oscillation (ENSO) phenomenon. Spectral and cross‐correlation analyses are developed between climatic indices of the tropical Pacific Ocean and the annual cycle of Colombia's hydrology: precipitation, river flows, soil moisture, and the Normalized Difference Vegetation Index (NDVI). Our findings indicate stronger anomalies during December‐February and weaker during March‐May. The effects of ENSO are stronger for streamflow than for precipitation, owing to concomitant effects on soil moisture and evapotranspiration. We studied time variability of 10‐day average volumetric soil moisture, collected at the tropical Andes of central Colombia at depths of 20 and 40 cm, in coffee growing areas characterized by shading vegetation (“shaded coffee”), forest, and sunlit coffee. The annual and interannual variability of soil moisture are highly intertwined for the period 1997–1999, during strong El Niño and La Niña events. Soil moisture exhibited greater negative anomalies during 1997–1998 El Niño, being strongest during the two dry seasons that normally occur in central Colombia. Soil moisture deficits were more drastic at zones covered by sunlit coffee than at those covered by forest and shaded coffee. Soil moisture responds to wetter than normal precipitation conditions during La Niña 1998–1999, reaching maximum levels throughout that period. The probability density function of soil moisture records is highly skewed and exhibits different kinds of multimodality depending upon land cover type. NDVI exhibits strong negative anomalies throughout the year during El Niños, in particular during September–November (year 0) and June–August (year 0). The strong negative relation between NDVI and El Niño has enormous implications for carbon, water, and energy budgets over the region, including the tropical Andes and Amazon River basin.