Showing papers in "Journal of The American Water Resources Association in 2022"

Quantifying Streamflow Depletion from Groundwater Pumping: A Practical Review of Past and Emerging Approaches for Water Management

Abstract: Groundwater pumping can cause reductions in streamflow (“streamflow depletion”) that must be quantified for conjunctive management of groundwater and surface water resources. However, streamflow depletion cannot be measured directly and is challenging to estimate because pumping impacts are masked by streamflow variability due to other factors. Here, we conduct a management‐focused review of analytical, numerical, and statistical models for estimating streamflow depletion and highlight promising emerging approaches. Analytical models are easy to implement, but include many assumptions about the stream and aquifer. Numerical models are widely used for streamflow depletion assessment and can represent many processes affecting streamflow, but have high data, expertise, and computational needs. Statistical approaches are a historically underutilized tool due to difficulty in attributing causality, but emerging causal inference techniques merit future research and development. We propose that streamflow depletion‐related management questions can be divided into three broad categories (attribution, impacts, and mitigation) that influence which methodology is most appropriate. We then develop decision criteria for method selection based on suitability for local conditions and the management goal, actionability with current or obtainable data and resources, transparency with respect to process and uncertainties, and reproducibility.

Decision Science Can Help Address the Challenges of Long‐Term Planning in the Colorado River Basin

Abstract: “Deep uncertainty” is a term that describes planning contexts in which it is impossible to determine the likelihood of any given set of future conditions, there are conflicting performance objectives and priorities, and decision outcomes are unpredictable. Evidence of the relevance of this term in the Colorado River Basin can be found in the unexpected severity and length of the ongoing drought, the existence of a wide range of future streamflow and demand projections and anticipated system requirements, as well as in the diverse range of stakeholders, viewpoints, and priorities that must be considered when developing and analyzing future operating policies. Decision Making under Deep Uncertainty (DMDU) is a branch of decision science devoted to developing planning approaches that can address these challenges. Reclamation began exploring DMDU techniques in 2012 in the Colorado River Basin Water Supply and Demand Study when it used the concepts of adaptation, vulnerability, and robustness in the design and evaluation of portfolios of options and strategies to address a potential supply‐demand imbalance in coming decades. This article presents the basis for continuing to explore DMDU techniques and briefly describes how Reclamation’s recent and ongoing DMDU studies could contribute to future planning efforts in the Colorado River Basin.

Water‐Use Data in the United States: Challenges and Future Directions

Abstract: In the United States, greater attention has been given to developing water supplies and quantifying available waters than determining who uses water, how much they withdraw and consume, and how and where water use occurs. As water supplies are stressed due to an increasingly variable climate, changing land‐use, and growing water needs, greater consideration of the demand side of the water balance equation is essential. Data about the spatial and temporal aspects of water use for different purposes are now critical to long‐term water supply planning and resource management. We detail the current state of water‐use data, the major stakeholders involved in their collection and applications, and the challenges in obtaining high‐quality nationally consistent data applicable to a range of scales and purposes. Opportunities to improve access, use, and sharing of water‐use data are outlined. We cast a vision for a world‐class national water‐use data product that is accessible, timely, and spatially detailed. Our vision will leverage the strengths of existing local, state, and federal agencies to facilitate rapid and informed decision‐making, modeling, and science for water resources. To inform future decision‐making regarding water supplies and uses, we must coordinate efforts to substantially improve our capacity to collect, model, and disseminate water‐use data.

Water Storage Decisions and Consumptive Use May Constrain Ecosystem Management under Severe Sustained Drought

Abstract: Drought has impacted the Colorado River basin for the past 20 years and is predicted to continue. In response, decisions about how much water should be stored in large reservoirs and how much water can be consumptively used will be necessary. These decisions have the potential to limit riverine ecosystem management options through the effect water‐supply decisions have on reservoir elevations. We used projected hydrology and river temperatures to compare the outcome of combinations of water storage scenarios and consumptive use limits on metrics associated with ecosystem management of the Colorado River in Grand Canyon. Ecosystem management metrics included the ability to implement designer flows, temperature suitability for fishes, and fragmentation. We compared current water management operations to prioritizing storage in either Lake Mead or Lake Powell combined with three levels of consumptive use. Projected reservoir levels limited environmental flow delivery and increased fragmentation regardless of where water was stored if consumptive use was not limited. Warmer river temperatures associated with low reservoir levels are likely, creating suitable conditions for non‐native species of concern, such as smallmouth bass. Water storage decisions provided variability and management flexibility, but water storage was less important when less water was available, highlighting the importance of keeping water in the system to provide flexibility for achieving ecosystem goals.

DSWEmod — The Production of High‐Frequency Surface Water Map Composites from Daily MODIS Images

Abstract: Optical satellite imagery is commonly used for monitoring surface water dynamics, but clouds and cloud shadows present challenges in assembling complete water time series. To test whether the daily revisit rate of Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery can reduce cloud obstruction and improve high‐frequency surface water mapping, we compared map results derived from Landsat (30‐m) and MODIS (250‐m) data across the state of California for 2003–2019. We adapted the Dynamic Surface Water Extent (DSWE) model in Google Earth Engine to generate surface water map composites from MODIS imagery every 5, 10, 15, and 30 days, and compared products to monthly Landsat‐based DSWE maps. Results for DSWEmod (DSWE MODIS) in California suggest that more than 5% data loss (cloud obstruction, etc.) was present in only 2% of the 15‐day time series, as compared to 32% of the monthly Landsat DSWE time series. The five‐day DSWEmod composites averaged 8.4% obscuration in the winter months. Area estimates derived from cloud‐filtered MODIS and Landsat monthly products have the highest linear correlations compared to streamgage discharge records, suggesting that monthly scale analyses best explain the relationship between surface water area and general streamflow dynamics. Shorter‐interval DSWEmod products have lower correlations but utility for understanding the timing of surface water peaks and past flood events.

Machine Learning Assisted Reservoir Operation Model for Long‐Term Water Management Simulation

Abstract: This study explores strategies for long‐term reservoir simulations by combining generic rule‐based reservoir management model (RMM) and machine learning (ML) models for two major multipurpose reservoirs — Allatoona Lake and Lake Sidney Lanier in the southeastern United States. First, a standalone RMM is developed to simulate daily release and storage during Water Year 1981–2015. Next, using Long‐Short Term Memory (LSTM) as the ML technique, a standalone LSTM model is trained based on reservoir inflow and meteorological observations to simulate reservoir release and estimate reservoir storage through water balance calculation. Three hybrid modeling strategies are developed, one using RMM output as an additional LSTM input (H1), another using LSTM as the initial release estimate in RMM (H2), and the third combining the first two strategies (H3). The Nash–Sutcliffe efficiency (NSE) for release (NSE‐r), storage (NSE‐s), and their mean (NSE‐avg) are used for model evaluation. Overall, H1 improves NSE‐r to 0.65 and 0.54 for Allatoona and Lanier, respectively, compared to standalone RMM (0.44 and 0.21); however, its storage trajectory did not produce a physically feasible solution, similar to LSTM. H2 and especially H3 show that they can retain the best features from RMM and LSTM, with H3 NSE‐avg being 0.695 and 0.55 for Allatoona and Lanier outperforming RMM (0.615 and 0.29). The findings suggest a robust simulation capacity for large‐scale water management in future studies.

Climate Change Impacts on Agricultural Water Availability in the Middle Rio Grande Basin

Abstract: We present a comprehensive analysis of water availability under plausible future climate conditions in a heavily irrigated agricultural watershed located in the middle section of the Rio Grande Basin in the United States Desert Southwest. Future managed streamflow scenarios (through year 2099) were selected from among 97 scenarios developed based on downscaled, bias‐corrected global climate model outputs to evaluate future inflows to the principal surface water storage reservoirs, possible future reservoir releases, and groundwater pumping to sustain irrigated agriculture. The streamflow projections describe a wide range of dry and wet conditions compared to the average historical flows in the river, indicating significant uncertainty in future water availability in the Rio Grande Basin. We applied the Soil and Water Assessment Tool to illustrate the impact of climate futures on different components of the water budget at a watershed scale. Results indicate declining reliability of reservoir storage to meet the water demand of irrigated agriculture. The impact of declining surface water can be offset by increasing the pressure on the already‐strained groundwater resources. However, the region should be prepared to use slightly saline (total dissolved solids [TDS] > 1,000 mg/L) and moderately saline groundwater (TDS > 3,000 mg/L) as fresh groundwater in the regional aquifer is depleted within the 21st Century under hotter and drier conditions and status quo agricultural land and water management practices.

Confronting our Agricultural Nonpoint Source Control Policy Problem

Abstract: Federal and state agricultural and environmental agencies have spent enormous sums since the 1990s to reduce nonpoint source (NPS) water pollution from agriculture. Yet, water quality problems are pervasive, and agriculture is a major cause. The lack of progress is often attributed to insufficient funding for pollution control practices relative to the scale of the problem. However, we attribute the lack of progress to shortcomings in agricultural NPS pollution control policy. We illustrate our argument after considering nearly four decades of federal, state, and local efforts to reduce agricultural NPS pollution to the Chesapeake Bay. Additional funding for current programs, absent fundamental program reform, is unlikely to produce reductions from agriculture needed to achieve desired water quality outcomes.

The Press and Pulse of Climate Change: Extreme Events in the Colorado River Basin

Abstract: Extremes in temperature and precipitation are associated with damaging floods, prolonged drought, destructive wildfires, agricultural challenges, compromised human health, vulnerable infrastructure, and threatened ecosystems and species. Often, the steady and progressive trends (or presses) of rising global temperature are the central focus in how climate impacts are described. However, observations of extreme weather events (or pulses) increasingly show that the intensity, duration and/or frequency of acute events are also changing, resulting in greater impacts on communities and the environment. Describing how the influence of extreme events may shape water management in the Colorado River Basin in clear terms is critical to sound future planning and efforts to manage risk. Three scenario planning workshops in 2019 and 2020 were held as part of a Colorado River Conversations series, identifying potential impacts from multiple intersecting extreme events. Water managers identified climate‐related events of concern in the Colorado River Basin that necessitate greater attention and adaptive responses. To support efforts to include consideration of climate‐change‐driven extremes in water management and planning, we explore the current state of knowledge at the confluence of long‐term climate shifts and extreme weather in the Colorado River Basin related to the events of concern that were identified by scenario planning participants.

Evaluating the Impact of Low Impact Development Practices on the Urban Flooding over a Humid Region of China

Abstract: Global warming and the rapid development of urbanization increase the likelihood of the occurrence of urban inundation, causing serious economic losses and threats to people's lives. Low impact development (LID) practices have attracted increasing attention as an effective approach which can mitigate urban inundation to some extent. Investigating the impact of LID practices on urban inundation is of significant importance to the prevention and control of urban flooding. This study constructed a coupling model with the combination of Storm Water Management Model and a 2D hydrodynamic model to provide a comprehensive simulation of urban inundation. The inundation situations are simulated with various scenarios by considering the implementation of LID practices under various rainfall return periods in Wuhan, China. We found that the LID practices can be more effective for urban inundation mitigation under rainfall events with smaller magnitude, and its ability in reducing the flood risk is weakened for extreme rainfall events. The results showed that LID practices can reduce the inundation area by 22.52%–38.9%. Especially for the inundation area with water depth larger than 0.4 m, the LID practices can reduce the inundation area by 71.52%–88.73% under different scenarios. Besides, the LID practices have a certain impact on the inundation area affecting traffic with a reduced rate of 37.2%–90.06%. This study can provide scientific support and a potential guiding significance for the future implementation of LID practices in cities under similar construction conditions.

Estimating Facility‐Level Monthly Water Consumption of Commercial, Industrial, Municipal, and Thermoelectric Users in Virginia

Abstract: Understanding water consumption is an important component of water management. However, water consumption data are limited and consumption coefficients do not account for variability through time and across users. This study combines federally maintained discharge data with state‐maintained withdrawal data at monthly time steps to estimate facility‐level and spatially aggregated water consumption in Virginia between 2010 and 2016. We evaluate (1) the feasibility of using discharge and withdrawal datasets to estimate sub‐annual water consumption, (2) how these consumption estimates vary depending on the level of spatial aggregation, and (3) what patterns of seasonality exist in consumption estimates. We find that a combined process of text matching and geospatial analysis is effective in matching facilities and yielding monthly time‐series of water consumption. Our results suggest that median consumption in industrial (17%) and commercial (19%) facilities may be higher than median consumption coefficients in the literature (10%). Consumption estimates also demonstrated more variability across facilities and seasons than aggregate coefficients in the literature suggest. Combining this approach with institutional knowledge can assist in quantifying issues such as inter‐basin transfers and infiltration that impact consumption estimates, ultimately allowing for more accurate accounts of water use and availability.

Effect of Restoration on Plant Greenness and Water Use in Relation to Drought in the Riparian Corridor of the Colorado River Delta

Abstract: Revitalization of the Colorado River delta riparian corridor and increasing riparian plant greenness and water use may be accomplished by added water and restoration efforts to offset declines measured since 2000 by Landsat. We use the two‐band Enhanced Vegetation Index (EVI2; a proxy for greenness) and evapotranspiration (ET, mm/day) using EVI2 and potential ET(ETo) from Yuma Valley. We assess if restoration with only 7.5% landcover had an impact on the unrestored reach‐level landcover by measuring these two metrics, EVI2 and ET(EVI2) by comparing restored and unrestored areas. A key finding is that over 21‐years EVI2 in the unrestored corridor decreased by 23.6% and ET(EVI2) decreased by 32% (0.87 mm/day). Since 2011, the unrestored reaches lost EVI2 (11%) and −0.73 mm/day ET(EVI2) (28%), but restored sites increased in EVI2 (36%) and 0.58 mm/day ET(EVI2) (20%). Water delivered to restored sites increased EVI2 by 33.6% and 1.29 mm/day ET(EVI2) (58%). EVI2 and ET(EVI2) as a function of the Standardized Precipitation Evapotranspiration Index for drought periods highlight that restored and unrestored sites respond differently. Unrestored reaches are in decline; restored sites show increases in EVI2 and ET(EVI2). Restored sites do not have a significant impact on unrestored adjacent area, but smaller surface flows, a greater reliance on directed agricultural return flows, and deliveries of water to active restoration sites have revitalized habitat and increased ecosystem services in the delta.

Nutrient Retention and Release in Eroding Chesapeake Bay Tidal Wetlands

Abstract: The worldwide loss of coastal wetlands has traditionally been addressed as the loss of ongoing nutrient retention ecosystem services. However, nutrient remineralization from eroded particles may further exacerbate water quality degradation. Using data on nutrient burial and denitrification from northern Chesapeake Bay, along with estimates of the bioavailability of eroded marsh particulates, the changing role of wetlands as an important sink for nutrients is examined. Although the erosion of wetlands results in the reintroduction of nitrogen and phosphorus into open‐water habitats, the potential for exacerbating eutrophication is highly diminished by the low lability of wetland organic matter. The impact of such erosion on the cycling of Fe‐bound phosphorus from marsh soils is highly dependent on both the amount of inorganic P, its solid phase association with Fe, and its potential remobilization from the estuarine sediments into which it is deposited. Although nutrient sequestration in newly constructed wetlands built from dredged materials suggested a rapid development of nutrient sequestration, a better understanding of nutrient ecosystem services provided by marshes created by transgression into uplands is necessary for understanding the long‐term nutrient retention value of coastal wetlands.

Operationalizing equity for integrated water resources management

Abstract: Advancing social equity has been implicitly and explicitly central to water resources policy for decades. Yet, equity remains largely outside of standard water resources planning and management practices. Inclusion of equity within water resources infrastructure is inhibited by barriers including an incomplete conceptual understanding of equity, a perceived lack of quantitative and qualitative equity metrics, unclear connections between equity and standard project planning frameworks, and the absence of concrete examples. To facilitate greater practical inclusion of social equity in water resources practices, we describe equity relative to dimensions of distribution, procedure, and recognition and identify metrics associated with each. We then map these dimensions of equity onto different stages of a water resources project life cycle. We discuss how inequities are often perpetuated by current approaches and highlight case studies that promote one or more of the facets of equity. Rather than providing a prescriptive solution to “achieve” equity within water resources practices, we emphasize the need for contextualized approaches that include pragmatic steps toward more equitable practices and outcomes.

Reconceptualizing HRU Threshold Definition in the Soil and Water Assessment Tool

Abstract: The Soil and Water Assessment Tool (SWAT) model simulates a watershed by dividing it into subbasins which are further divided into hydrologic response units (HRUs). User‐defined area thresholds for land use, soil, and slope are often used when defining HRUs during model setup to improve computational efficiency by reducing the number of HRUs. This, however, results in loss of watershed biophysical information due to the reapportionment of HRUs that fail to exceed the threshold to other dominant HRUs. This study presents an improved HRU definition method that minimizes the loss of watershed biophysical information without considerably increasing the number of HRUs and lowering the user‐defined HRU thresholds. Comparison of land use and soil distribution showed that the new HRU model closely matched the no‐threshold full HRU model, unlike the default threshold SWAT model in which the landscape distribution characteristics were inadequately represented. Simulated hydrological and water quality variables, as well as model parameterization, were also better characterized when using the proposed HRU definition method when compared with the default SWAT model. The number of HRUs with the new method (934) was only slightly higher than the default threshold model (589) but considerably lower than the full HRU model (29,288). This new HRU definition method can help modelers perform computationally efficient modeling without compromising the accuracy of biophysical inputs to the model.

Ephemeral Stream Network Extraction from Lidar‐Derived Elevation and Topographic Attributes in Urban and Forested Landscapes

Abstract: Under‐representations of headwater channels in digital stream networks can result in uncertainty in the magnitude of headwater habitat loss, stream burial, and watershed function. Increased availability of high‐resolution (<2 m) elevation data makes the delineation of headwater channels more attainable. In this study, elevation data derived from light detection and ranging was used to predict ephemeral stream networks across a forested and urban watershed in the Maryland Piedmont USA. A method was developed using topographic openness (TO) and wetness index to remotely predict the extent of stream networks. Predicted networks were compared against a comprehensive field survey of the ephemeral network in each watershed to evaluate performance. Comparisons were also made to the U.S. Geological Survey National Hydrography Dataset (NHD) and a flow accumulation approach where a single drainage area threshold defined channel initiation. Although the NHD and flow accumulation methods resulted in low commission errors, omission errors were highest in these networks. The TO‐based networks detected a larger number of ephemeral channels, but with higher commission error. Small ephemeral channels with less defined banks or originating at groundwater seeps were difficult to detect in all methods. Comparisons between forested and urban watersheds also highlight the difficulty of identifying headwater channels using topographic attributes in human‐modified landscapes.

Risk Assessment of the Water Resources Carrying Capacity: A Case Study in North China

Abstract: Evaluating the water resources carrying capacity (WRCC) is the prerequisite and foundation for the planning and management of water resources. In this paper, according to risk theory, a framework for the risk assessment of WRCC was proposed based on the fragility of damage‐affected bodies and the damage posed by disaster‐inducing factors. Then, based on water quantity, water quality, water area, and water flow, a fragility index system was constructed from the water resources, economy, and society category. Additionally, the damage was analyzed in terms of climate change, urbanization, and industrialization. Finally, a model for the risk assessment of the WRCC was established by combining the fragility of the water resources carrying system with the compound damage posed by climate change, urbanization, and industrialization. The developed model was then applied to assess the risk of the WRCC in North China in 2017. The results indicate that the fragility of the WRCC was the highest in the Beijing–Tianjin–Hebei region, and the compound damage showed an increasing trend from the southeast to the northwest in North China. Meanwhile, the risk of the WRCC decreased from the southeast to the northwest, the highest risk was observed in Hebei Province, and the lowest risk was observed in Inner Mongolia. This research provides an important technical guideline for the sustainable utilization of water resources and the coordinated development of the economy and society.

Predicting Near‐Term Effects of Climate Change on Nitrogen Transport to Chesapeake Bay

Abstract: Understanding effects of climate change on nitrogen fate and transport in the environment is critical to nutrient management. We used climate projections within a previously calibrated spatially referenced regression (SPARROW) model to predict effects of expected climate change over 1995 through 2025 on total nitrogen fluxes to Chesapeake Bay and in watershed streams. Assuming nitrogen inputs and other watershed conditions remain at 2012 levels, effects of increasing temperature, runoff, streamflow, and stream velocity expected between 1995 and 2025 will include an estimated net 6.5% decline in annual nitrogen delivery to the bay from its watershed. This predicted decline is attributable to declines in the delivery of nitrogen from upland nonpoint sources to streams due to predicted warmer temperatures. Such temperature‐driven declines in the delivery of nitrogen to streams more than offset predicted increased delivery to and within streams due to increased runoff and streamflow and may be attributable to increasing rates of denitrification or ammonia volatilization or to changes in plant phenology. Predicted climate‐driven declines in nitrogen flux are generally similar across the watershed but vary slightly among major nonpoint source sectors and tributary watersheds. Nitrogen contributions to the bay from point sources are not affected by temperature‐driven changes in delivery from uplands and are therefore predicted to increase slightly between 1995 and 2025.

Assessing the Effectiveness of Winter Cover Crops for Controlling Agricultural Nutrient Losses

Abstract: A nutrient loss reduction strategy is necessary to guide the efforts of improving water quality downstream of an agricultural watershed. In this study, the effectiveness of two winter cover crops, namely cereal rye and annual ryegrass, is explored as a loss reduction strategy in a watershed that ultimately drains into a water supply reservoir. Using a coupled optimization‐watershed model, optimal placements of the cover crops were identified that would result in the tradeoffs between nitrate‐N losses reduction and adoption levels. Analysis of the 10%, 25%, 50%, and 75% adoption levels extracted from the optimal tradeoffs showed that the cover crop placements would provide annual nitrate‐N loss reductions of 3.0%–3.7%, 7.8%–8.8%, 15%–17.5%, and 20.9%–24.3%, respectively. In addition, for the same adoption levels (i.e., 10%–75%), sediment (1.8%–17.7%), and total phosphorus losses (0.8%–8.6%) could be achieved. Results also indicate that implementing each cover crop on all croplands of the watershed could cause annual water yield reduction of at least 4.8%, with greater than 28% in the months of October and November. This could potentially be detrimental to the storage volume of the downstream reservoir, especially in drought years, if cover crops are adopted in most of the reservoir's drainage area. Evaluating water yield impacts, particularly in periods of low flows, is thus critical if cover crops are to be considered as best management practices in water supply watersheds.

An Assessment of Potential Severe Droughts in the Colorado River Basin

Abstract: Much has been learned about Colorado River hydrology since the severe sustained drought study in 1995. We summarize our updated understanding of plausible future drought conditions by considering historical flows, tree‐ring reconstructions, and climate change. We focus on natural streamflow at Lees Ferry, the primary metric used to quantify the runoff in the Colorado River Basin. We identify drought periods using historical records and tree‐ring reconstructed streamflow at Lees Ferry, which we then use to characterize potential future droughts. Resampling from past drought periods generates plausible future conditions to consider during planning. We produced three drought scenarios, each comprising 100 streamflow sequences to be used as input to systems operation and management models. We used analysis of the duration‐severity and cumulative deficit relative to the mean natural flow to evaluate droughts and drought simulations and show that the current millennium drought that started in 2000 has an average flow far less than the historical record. However, the flows reconstructed from tree rings or future flows projected from climate models indicate that even more severe droughts are possible. When used as input to the Colorado River Simulation System the drought scenarios developed indicate considerable periods when Lake Powell falls below its hydropower penstocks, indicating a need to rethink management and operation of these reservoirs during these critical conditions.

Potential impacts of reduced inflows to the Salton Sea: Forecasting non‐market damages

Abstract: Terminal lakes throughout the American West provide important amenity and environmental values, but many are shrinking due to reduced inflows and warming temperatures. In California's Imperial Valley, agricultural water use reductions diminish inflows supporting the Salton Sea, a terminal desert lake and important environmental amenity for both the region and the state as a whole. The costs of these reduced inflows are difficult to monetize yet complicate management decisions. We assess the costs of potential future drought‐induced transfers by linking novel hydrologic scenarios to an economic framework for quantifying local and regional damages based on existing estimates of non‐market environmental values from the literature. The costs of lost wetland ecosystems, increases in particulate matter from exposed playa, and other local disamenities are substantial. For the scenarios considered, they range between approximately $500 million and $1 billion in present value (2019 USD). Estimated damages per acre‐foot (or thousand m3) of reallocated water exceed several thousand dollars. The majority arise from loss of wetland habitat; incremental particulate matter damages are relatively modest in our modeling but exacerbate salient air quality issues in the region. Interest in reallocating water from Imperial Valley, the largest user of Colorado River water, to other applications will increase over time. Our work highlights the importance of evaluating the impacts of such efforts.

Individualized and Combined Effects of Future Urban Growth and Climate Change on Irrigation Water Use in Central Arizona

Abstract: Irrigation in agricultural and urban settings is responsible for nearly 80% of the water use in the Phoenix Metropolitan Area. Over the last three decades, there has been a continuous decrease in cropland area and its water consumption. Meanwhile, urbanization has increased outdoor irrigation to maintain residential areas and parks. Given these trends, irrigation water use (IWU) is subject to large uncertainties which challenge land and water management. In this work, we used a land surface model with an irrigation module to quantify urban and agricultural IWU under the individualized and combined effects of future urban growth and anticipated climate change. A large set of scenario combinations (96 in total) allowed us to bracket plausible pathways of IWU change in the 21st Century. We found that land use change reduced IWU by −4.6% to −0.1% due to savings from crop‐urban conversion, while climate change effects led to increases in IWU by +3.8% to +8.6%. When combined, total IWU changed from +2.5% to +5.8% in the intermediate future (2041–2070) and from −0.5% to 6.8% in the far future (2071–2100). These outcomes suggest that water savings from land use change will likely not be able to compensate for the increasing demand from urban irrigation when considering climate change, under current irrigation practices. Our approach to model the interconnections between land and water under climate change can be used to support sustainable water planning in cities in other arid regions.

Evaluation of Select Velocity Measurement Techniques for Estimating Discharge in Small Streams across the United States

Abstract: Multiple instruments and methods exist for collecting discrete streamflow measurements in small streams with low flows, defined here as less than 5.7 m3/s (200 ft3/s). Included in the available methods are low‐cost approaches that are infrequently used, in part, because their uncertainty is not well known. In this work, we evaluated the accuracy and suitability of three low‐cost velocity measurement methods (surface float [SF], velocity head rod [VR], and rising body [RB]) and three conventional current meters (acoustic Doppler velocimeter, and mechanical Price type AA and Price Pygmy meters) relative to discharge calculated from stable artificial hydraulic controls. A total of 231 measurements were made by 20 individuals during 88 site visits to 24 sites in eight states. Accuracies were assessed for all methods and precision was evaluated for the low‐cost methods. The median percent error was below 5% for conventional methods, and below 20% for the low‐cost methods. The SF was the most accurate (median absolute percent error 14%) and precise (mean percent precision of 11%) low‐cost method. The RB and VR, respectively, had 15% and 20% median absolute percent error and 29% and 12% mean percent precision. Results suggest that low‐cost methods, when used appropriately, can be used to estimate discharge data under low flow conditions when measurements with conventional methods are not feasible and the associated accuracies meet end‐user measurement objectives.

Lake management under severe drought: Lake Mead, Nevada/Arizona

Abstract: Drought can affect both the quantity and quality of water in lakes and reservoirs, yet larger, highly managed waterbodies, such as Lake Mead, may be somewhat buffered from drought effects. From 2000 to present, Lake Mead has experienced a 71% decline in volume; however, influent water quality has remained high and consistent outflow volumes through Hoover Dam have been maintained. Furthermore, management activities, such as increased removal of phosphorus by wastewater dischargers and legacy contamination cleanup efforts, have been initiated since the drought began. These efforts have led to small improvements in values of water quality parameters, such as phosphorus, nitrogen, and perchlorate, despite loss of volume for dilution of constituents, and consequently, decreased residence time. As the drought continues, Lake Mead is projected to continue declining in volume, inflows are projected to become warmer, and the population of Las Vegas is projected to grow, potentially adding additional stress to the hydrologic system. Maintenance of outflow may mitigate some potentially negative consequences, and understanding the drivers behind continued high water quality despite prolonged drought is important to continue to maintain the health and vitality of the entire Lower Colorado River Basin.

Near‐term forecasts of stream temperature using deep learning and data assimilation in support of management decisions

Abstract: Deep learning (DL) models are increasingly used to make accurate hindcasts of management‐relevant variables, but they are less commonly used in forecasting applications. Data assimilation (DA) can be used for forecasts to leverage real‐time observations, where the difference between model predictions and observations today is used to adjust the model to make better predictions tomorrow. In this use case, we developed a process‐guided DL and DA approach to make 7‐day probabilistic forecasts of daily maximum water temperature in the Delaware River Basin in support of water management decisions. Our modeling system produced forecasts of daily maximum water temperature with an average root mean squared error (RMSE) from 1.1 to 1.4°C for 1‐day‐ahead and 1.4 to 1.9°C for 7‐day‐ahead forecasts across all sites. The DA algorithm marginally improved forecast performance when compared with forecasts produced using the process‐guided DL model alone (0%–14% lower RMSE with the DA algorithm). Across all sites and lead times, 65%–82% of observations were within 90% forecast confidence intervals, which allowed managers to anticipate probability of exceedances of ecologically relevant thresholds and aid in decisions about releasing reservoir water downstream. The flexibility of DL models shows promise for forecasting other important environmental variables and aid in decision‐making.

Development of a Field Scale SWAT+ Modeling Framework for the Contiguous U.S.

Abstract: The Soil and Water Assessment Tool (SWAT) model is commonly used to predict the impacts of agricultural practices on water quality and quantity. Although widely applied, the data framework used to drive SWAT in the United States (U.S.) is fragmented and inconsistent, varying by user and model interface. This research describes the development of the National Agroecosystems Model (NAM), which provides a unified field to national scale modeling computational framework for research and decision support by using the latest SWAT platform, dubbed SWAT+. NAM has sufficient detail to capture field‐level processes and management actions and spans the full extent of the contiguous U.S. NAM contains 7 million computational units, 4 million of which represent specific cultivated fields. It contains 3 million individually identifiable stream segments and more than 5,000 reservoirs. NAM is intended to serve as a reasonable base framework to be refined for specific applications. This work describes the individual data sources, assumptions, and the processing steps for their inclusion. NAM is constructed with 2,121 individual SWAT+ models which can be executed in a parallel hierarchical structure to dramatically improve runtime. This framework was tested in a case study of the Little River Watershed, Tifton, GA. NAM is developed using only publicly available data sources such that subsets of it can be shared to support research with other government agencies, universities, and others in the public domain.

Champions and Traditional Technocrats: The Role of Environmental Value Orientation in Stormwater Management

Abstract: The paper examines relationships between stormwater control measure (SCM) priorities and environmental value orientations among stormwater managers in Cleveland, Ohio and Denver, Colorado, metro regions with contrasting environmental conditions and policy contexts. While studies show that governance explains differences in broad SCM priorities, less is known about what motivates individual “street level bureaucrats” who influence decisions at the project level. Drawing from cognitive social science perspectives, this study surveyed stormwater professionals (n = 185) about primary and co‐benefit SCM priorities and environmental value orientation. Results revealed different primary SCM priorities by region: Cleveland and Denver respondents prioritized quantity and quality goals, respectively, reflecting regional context. Co‐benefit priorities correlated to two environmental value orientation clusters — “Traditional Technocrats” with relatively anthropocentric orientations and “Champions” with relatively ecocentric orientations — who were equally abundant in both regions. Findings suggest that environmental value orientation influences co‐benefit priorities, which may have implications for project level articulation of policy.

Application of a Large‐Scale Terrain‐Analysis‐Based Flood Mapping System to Hurricane Harvey

Abstract: Flood modeling provides inundation estimates and improves disaster preparedness and response. Recent development in hydrologic modeling and inundation mapping enables the creation of such estimates in near real time. To quantify their performance, these estimates need to be compared to measurements collected during historical events. We present an application of a flood mapping system based on the National Water Model and the Height Above Nearest Drainage method to Hurricane Harvey. The outputs are validated with high‐water marks collected to record the highest water levels during the flood. We use these points to compute elevation‐related variables and flood extents and measure the quality of the estimates. To improve the performance of the method, we calibrate the roughness coefficient based on stream order. We also use lidar data with a workflow named GeoFlood and we compare the modeled inundation to that recorded by the high‐water marks and to the maximum inundation extent provided by the Dartmouth Flood Observatory based on remotely sensed data from multiple sources. The results show that our mapping system estimates local water depth with a mean error of about 0.5 m and that the inundation extent covers over 90% of that derived from high‐water marks. Using a calibrated roughness coefficient and lidar data reduces the mean error in flood depth but does not affect as much the inundation extent estimation.

Featured Collection Introduction: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later — Part I

Abstract: In the 1970s, Water Resources Research institutes and centers from Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming formed the Powell Consortium (in honor of John Wesley Powell) to work on water resource challenges in the Colorado River and Great Basin regions. Collaborative research supported by the Consortium led to a set of studies published more than 25 years ago in a special issue of the Water Resources Bulletin, which later became the Journal of the American Water Resource Association (JAWRA). That special issue, “Severe Sustained Drought: Managing the Colorado River System in Times of Water Shortage,” brought together expertise from diverse fields: anthropology, dendrochronology, economics, engineering, geography, hydrology, law, and sociology to examine potential economic and environmental impacts of extreme, prolonged drought in the Colorado River Basin. Historically, surface water availability from the Colorado River Basin has been measured in terms of annual native flows at Lees Ferry, just below Glen Canyon Dam. The Colorado River Compact of 1922 and the 1944 Water Treaty with Mexico allocated 7.5 million acre feet (maf) each to the Upper and Lower Basins and 1.5 maf to Mexico for a total of 16.5 maf (Table 1). At the time of the Sustained Severe Drought (SSD) study, historical measurements placed flows at only 15.2 maf, while tree ring reconstructions over a longer period placed flows at just 13.5 maf (Stockton and Jacoby 1976; Young 1995). Thus at the time of that SSD study, it was recognized that the Colorado River was over-allocated, even absent drought. Tree-ring research indicated the Basin had, long ago, experienced longer and more severe droughts than any known in modern records; the most severe multi-decade drought occurred in the 1500s. The organizing device for the different studies was a hypothetical multi-decade drought based on, but not identical to, this historically severe drought. The SSD created a Colorado Rearranged Severe Drought scenario by assuming flow reductions were moved to the beginning of the time frame, with declines increasing every year so that annual flows bottomed out in the 16th year (Tarboton 1995). The 16-year average of flows was 9.6 maf. This rearranged scenario served as the basis for SSD analysis. This special issue considered the questions of, if such a drought began in the 1990s, what would be the impacts on the hydrological system, including operation and management of the federal reservoir systems? What would be the economic and environmental impacts of these hydrologic shocks and how would they be conditioned by existing water laws and institutions? What types of legal and policy responses might be needed to ameliorate negative drought impacts?

Select Water Quality Parameters during Wet and Dry Conditions in the Colorado River Delta

Abstract: The Colorado River Delta (CRD) consists of agricultural fields and remnant wetlands that are sustained by the Colorado River and agricultural drainage. Electrical conductivity (EC), dissolved oxygen, and ammonia‐nitrogen data were collected at different locations in the CRD at the end of a wet period in 2000 and compared with the concentrations present during the dry conditions that prevailed from 2001 to 2020. An increase in mean EC values measured by the International Boundary and Water Commission at Morelos Dam between wet (1.2 ± 0.06 mS/cm) and dry (1.4 ± 0.11 mS/cm) periods was observed. The same was also observed at reach 4 of the riparian corridor between the wet (2.4 ± 0.24 mS/cm) and dry (3.3 ± 0.75 mS/cm) periods with an increasing trend in salinity over the years. However, salinity values did not exceed the limits required for the growth of native trees and cattails. A positive result was that EC values at reach 6 and the Hardy River significantly decreased over the past 13 years, this was attributed to inflows from “Arenitas” Water Treatment Plant and its wetland that began operations in 2008. Finally, although severe drought will likely mean water shortages, results indicate that treated water can maintain and restore riparian corridors and wetlands. It is recommended that ongoing conservation efforts consider these local water sources in addition to the ecological pulse flows.