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Observations are used to examine how soil moisture influences the surface radiation budget, ground heat flux, and available energy in semiarid environments. Defining this relationship is critical to understand interactions between the land surface and the atmosphere, in particular assessing if a feedback exists between soil moisture and rainfall anomalies. We use two summers of data collected from semiarid grassland and shrubland ecosystems in central New Mexico. The response of surface radiation budget components and other variables to soil moisture variations are quantified via linear regression. Then, the variations are scaled over the observed range of soil moisture (15% volumetric water content). The soil temperature...
Relations between stream water chemistry and topographic, vegetative, and geologic characteristics of basins were evaluated for nine alpine/subalpine basins in Rocky Mountain National Park, Colorado, to identify controlling parameters and to better understand processes governing patterns in stream water chemistry. Fractional amounts of steep slopes (≥30°), unvegetated terrain, and young surficial debris within each basin were positively correlated to each other. These terrain features, which commonly occur on steep valley side slopes underlain by talus, were negatively correlated with concentrations of base cations, silica, and alkalinity and were positively correlated with nitrate, acidity, and runoff. These...
Updated proxy reconstructions of water year (October?September) streamflow for four key gauges in the Upper Colorado River Basin were generated using an expanded tree ring network and longer calibration records than in previous efforts. Reconstructed gauges include the Green River at Green River, Utah; Colorado near Cisco, Utah; San Juan near Bluff, Utah; and Colorado at Lees Ferry, Arizona. The reconstructions explain 72?81% of the variance in the gauge records, and results are robust across several reconstruction approaches. Time series plots as well as results of cross-spectral analysis indicate strong spatial coherence in runoff variations across the subbasins. The Lees Ferry reconstruction suggests a higher...
Understanding and modeling precipitation isotope (?18O and ?D) patterns for large regions of the globe requires quantifying processes governing continental-scale climatology and hydrology. In this study, we have evaluated the extent to which inclusion of monthly moisture source temperature and moisture source locations in the Rayleigh distillation model aid in reproducing the relationships between monthly time series of precipitation isotope (?18O) values and temperature across the contiguous United States. The steepest isotope-temperature slopes (0.5??0.6? ?18O/�C) and greatest ?18O value correlations with temperature (r2 = 0.5?0.8), derived from 5 continuous years of the data from the United States Network for...
The marginal economic value of streamflow leaving forested areas in the Colorado River Basin was estimated by determining the impact on water use of a small change in streamflow and then applying economic value estimates to the water use changes. The effect on water use of a change in streamflow was estimated with a network flow model that simulated salinity levels and the routing of flow to consumptive uses and hydroelectric dams throughout the Basin. The results show that, under current water management institutions, the marginal value of streamflow in the Colorado River Basin is largely determined by nonconsumptive water uses, principally energy production, rather than by consumptive agricultural or municipal...
Relationships between vegetation and hydrologic measurements for 17 watersheds near Grand Junction, Colorado, were subjected to correlation analyses. Six years of vegetation measurements, four vegetation measurement methods, and 15 years of hydrologic records were used in the analyses. Highly significant correlation coefficients were found for percent bare soil and runoff, but the relationships between bare soil and sediment yields were not statistically significant. Geomorphic parameters such as angle of junction, mean slope, drainage density, relief ratio, length-width ratio, and watershed area were more highly correlated with sediment yields than with runoff. Correlation coefficients for spring vegetation measurements...
Categorical forecasts of streamflow are important for effective water resources management. Typically, these are obtained by generating ensemble forecasts of streamflow and counting the proportion of ensembles in the desired category. Here we develop a simple and direct method to produce categorical streamflow forecasts at multiple sites. The method involves predicting the probability of the leading mode (or principal component) of the basin streamflows above a given threshold and subsequently translating the predicted probabilities to all the sites in the basin. The categorical probabilistic forecasts are obtained via logistic regression using a set of large-scale climate predictors. Application to categorical...
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We propose a multimodel ensemble forecast framework for streamflow forecasts at multiple locations that incorporates large-scale climate information. It has four broad steps: (1) Principal component analysis is performed on the spatial streamflows to identify the dominant modes of variability. (2) Potential predictors of the dominant streamflow modes are identified from several large-scale climate features and snow water equivalent information. (3) Objective criterion is used to select a suite of candidate nonlinear regression models each with different predictors. (4) Ensemble forecasts of the dominant streamflow modes are generated from the candidate models and are combined objectively to produce a multimodel...
High-elevation lakes in the western United States are sensitive to atmospheric deposition of sulfur and nitrogen due to fast hydrologic flushing rates, short growing seasons, an abundance of exposed bedrock, and a lack of well-developed soils. This sensitivity is reflected in the dilute chemistry of the lakes, which was documented in the U.S. Environmental Protection Agency's Western Lake Survey of 1985. Sixty-nine lakes in seven national parks sampled during the 1985 survey were resampled during fall 1999 to investigate possible decadal-scale changes in lake chemistry. In most lakes, SO4 concentrations were slightly lower in 1999 than in 1985, consistent with a regional decrease in precipitation SO4 concentrations...
A coupled unsteady flow and heat transport model is used to determine the impacts of fluctuating reservoir releases on downstream water temperatures. Maintenance of stream temperatures is one of the most common reasons cited for imposition of minimum flow requirements in regulated (reservoir controlled) rivers. Minimum flow constraints for temperature control are typically developed using worst-case scenarios (i.e., maximum air temperature, clear sky, etc.) of atmospheric conditions. We show that short- term modifications to reservoir releases based on local meteorological conditions can reduce the volume of water released, while still meeting temperature objectives. A case study of the Green River below Flaming...
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We present a data-driven model, Support Vector Machine (SVM), for long lead time streamflow forecasting using oceanic-atmospheric oscillations. The SVM is based on statistical learning theory that uses a hypothesis space of linear functions based on Kernel approach and has been used to predict a quantity forward in time on the basis of training from past data. The strength of SVM lies in minimizing the empirical classification error and maximizing the geometric margin by solving inverse problem. The SVM model is applied to three gages, i.e., Cisco, Green River, and Lees Ferry in the Upper Colorado River Basin in the western United States. Annual oceanic-atmospheric indices, comprising Pacific Decadal Oscillation...
Sulphur 35, a cosmogenically produced radioisotope with a short half-life (87 days), was measured in snowpack during 1993–1997 and at four locations within the Loch Vale watershed during 1995–1997. The four sites include the two main drainages in the watershed, Andrews Creek and Icy Brook, a small south facing catchment flowing into Andrews Creek (Andrews Spring 1), and a similar north facing catchment flowing out of a scree field into Icy Brook (Spring 19). Concentrations ranged from a high of almost 50 mBq/L for a sample from Spring 19 in June 1996 to a concentration near the detection limit for a sample from Andrews Creek in April 1997. Sulphur 35 concentrations were normalized to sulphate (as mBq/mg SO4−2)...
Understanding and modeling precipitation isotope (δ18O and δD) patterns for large regions of the globe requires quantifying processes governing continental-scale climatology and hydrology. In this study, we have evaluated the extent to which inclusion of monthly moisture source temperature and moisture source locations in the Rayleigh distillation model aid in reproducing the relationships between monthly time series of precipitation isotope (δ18O) values and temperature across the contiguous United States. The steepest isotope-temperature slopes (0.5‰–0.6‰ δ18O/°C) and greatest δ18O value correlations with temperature (r2 = 0.5–0.8), derived from 5 continuous years of the data from the United States...
The hydrologic, geomorphic, and ecologic effects of reservoir operations are thought to be key factors in the decline of native fishes in the upper Colorado River basin. The present paper examines the extent to which changes in streamflow and sediment loads have affected alluvial reaches of the Colorado River near Grand Junction, Colorado. The analysis shows that since 1950, annual peak discharges of the Colorado River and its major tributary, the Gunnison River, have decreased by 29-38%. The total volume of runoff delivered to the study area has not changed significantly over the period of record, but the annual hydrograph has been modified greatly by reductions in peak flows and augmentation of base flows. Annual...
High-altitude watersheds in the Front Range of Colorado show symptoms of advanced stages of nitrogen excess, despite having less nitrogen in atmospheric deposition than other regions where watersheds retain nitrogen. In two alpine/subalpine subbasins of the Loch Vale watershed, atmospheric deposition of NO3? plus NH4+ was 3.2?5.5 kg N ha?1, and watershed export was 1.8?3.9 kg N ha?1 for water years 1992?1997. Annual N export increased in years with greater input of N, but most of the additional N was retained in the watershed, indicating that parts of the ecosystem are nitrogen-limited. Dissolved inorganic nitrogen (DIN) concentrations were greatest in subsurface water of talus landscapes, where mineralization and...
Reliable predictions of sediment transport and river morphology in response to variations in natural and human-induced drivers are necessary for river engineering and management. Because engineering and management applications may span a wide range of space and time scales, a broad spectrum of modeling approaches has been developed, ranging from suspended-sediment “rating curves� to complex three-dimensional morphodynamic models. Suspended sediment rating curves are an attractive approach for evaluating changes in multi-year sediment budgets resulting from changes in flow regimes because they are simple to implement, computationally efficient, and the empirical parameters can be estimated from quantities that...
Population growth and a changing climate will tax the future reliability of the Colorado River water supply. Using a heuristic model, we assess the annual risk to the Colorado River water supply for 2008–2057. Projected demand growth superimposed upon historical climate variability results in only a small probability of annual reservoir depletion through 2057. In contrast, a scenario of 20% reduction in the annual Colorado River flow due to climate change by 2057 results in a near tenfold increase in the probability of annual reservoir depletion by 2057. However, our analysis suggests that flexibility in current management practices could mitigate some of the increased risk due to climate change–induced reductions...
We evaluated the sensitivity of The Loch, a subalpine lake in Rocky Mountain National Park in Colorado, to acidification in response to increased atmospheric loading of sulfur (S) and nitrogen (N) using the Model of Acidification of Groundwater in Catchments (MAGIC). Lake water acid-base chemistry was moderately sensitive to changes in both S and N deposition. However, the loads of S deposition that would drive chronic lake water acid neutralizing capacity (ANC) to below 0 or 20 ?eq L?1 were estimated to be 11 and 8 kg S ha?1 yr?1, respectively, assuming constant future N deposition at current levels. Comparable loads for N deposition, assuming constant future S deposition, were estimated to be 21 and 12 kg N ha?1...
Consideration is given to the costs in terms of regional income likely to be lost if irrigated acreages were to be reduced in the Upper Main Stem subbasin of the Colorado River as a means of freeing water for alternative uses and reducing salt loadings. The cost estimates, known to be biased upward, appear competitive with other water augmentation and salinity reduction programs. Published in Water Resources Research, volume 10, issue 5, on pages 893 - 897, in 1974.
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Given the importance of Upper Colorado River Basin (UCRB) snowpack as the primary driver of streamflow (water supply) for the southwestern United States, the identification of Pacific Ocean climatic drivers (e.g., sea surface temperature (SST) variability) may prove valuable in long-lead-time forecasting of snowpack in this critical region. Previous research efforts have identified El Ni�o?Southern Oscillation (ENSO) and Pacific Decadel Oscillation (PDO) as the main drivers for western U.S. snowpack, but these drivers have limited influence on regional (Utah and Colorado) UCRB snowpack. The current research applies for the first time the Singular Value Decomposition (SVD) statistical method to Pacific Ocean SSTs...
map background search result map search result map Identification of Pacific Ocean sea surface temperature influences of Upper Colorado River Basin snowpack A multimodel ensemble forecast framework: Application to spring seasonal flows in the Gunnison River Basin Using oceanic-atmospheric oscillations for long lead time streamflow forecasting A multimodel ensemble forecast framework: Application to spring seasonal flows in the Gunnison River Basin Using oceanic-atmospheric oscillations for long lead time streamflow forecasting Identification of Pacific Ocean sea surface temperature influences of Upper Colorado River Basin snowpack