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Water scarcity and fish imperilment driven by beef production

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Human consumption of freshwater is now approaching or surpassing the rate at which water sources are being naturally replenished in many regions, creating water shortage risks for people and ecosystems. Here we assess the impact of human water uses and their connection to water scarcity and ecological damage across the United States, identify primary causes of river dewatering and explore ways to ameliorate them. We find irrigation of cattle-feed crops to be the greatest consumer of river water in the western United States, implicating beef and dairy consumption as the leading driver of water shortages and fish imperilment in the region. We assess opportunities for alleviating water scarcity by reducing cattle-feed production, finding that temporary, rotational fallowing of irrigated feed crops can markedly reduce water shortage risks and improve ecological sustainability. Long-term water security and river ecosystem health will ultimately require Americans to consume less beef that depends on irrigated feed crops.
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1Sustainable Waters, Crozet, VA, USA. 2University of Virginia, Charlottesville, VA, USA. 3Water Asset Management, San Francisco, CA, USA. 4USDA
Forest Service, Southern Research Station, Otto, NC, USA. 5Department of Geography and Spatial Sciences, University of Delaware, Newark, DE, USA.
6Department of Plant and Soil Sciences, University of Delaware, Newark, DE, USA. 7Data Science Institute, Columbia University, New York, NY, USA.
8Darden School of Business, University of Virginia, Charlottesville, VA, USA. 9Twente Water Center, University of Twente, Enschede, The Netherlands.
10Institute of Water Policy, Lee Kuan Yew School of Public Policy, National University of Singapore, Singapore, Singapore. 11Institute of Urban Development,
Nanjing Audit University, Nanjing, Jiangsu, China. 12Civil Engineering Department, Kansas State University, Manhattan, KS, USA. 13Department of
Environmental Science, Baylor University, Waco, TX, USA. 14Robert B. Daugherty Water for Food Global Institute, University of Nebraska, Lincoln, NE, USA.
15Northern Arizona University, Flagstaff, AZ, USA. 16Lehigh University, Bethlehem, PA, USA. 17University of Victoria, Victoria, British Columbia, Canada.
Water shortages have afflicted human societies for thou-
sands of years1. As population centres grow and farmlands
expand, freshwater consumption typically increases until
renewable water supplies are fully utilized (for example, in Fig. 1);
at this point, water users and freshwater ecosystems become highly
vulnerable to water shortages during drier periods2. Historically,
water shortages had local causes and consequences, involving only
the communities that were directly dependent on an overused river
or aquifer. Today, however, with trade networks encircling the globe,
demand for asparagus in the United Kingdom can contribute to the
depletion of an aquifer in the Peruvian desert3,4 and water shortages
in the Central Valley of California can affect the availability and price
of almonds and pistachios imported into the European Union5.
Climate change exacerbates water shortages by affecting both
water supplies and water demands. Higher temperatures increase
evapotranspiration, reducing aquifer recharge and watershed run-
off6. For example, Udall and Overpeck attributed one-third of recent
declines in Colorado River flows (19% below average during 2000–
2014) to temperature increases7. The Intergovernmental Panel on
Climate Change expressed high confidence that irrigation—the
largest water-using sector globally—will increase in coming decades
due to increased evapotranspiration6.
Human-induced depletion of river flows has deleteriously
affected freshwater species and ecosystems across the globe8,9 and
is a leading cause of fish imperilment in the US1012. Richter etal.12
documented that 62% of sub-watersheds in the western US contain
at least one species endangered by flow depletion, with a total of 367
plant and animal species affected, including two-thirds of all native
fish species in the Colorado River basin. To protect species listed
under the US Endangered Species Act, water regulators have been
forced to curtail water use for irrigation in some watersheds, lead-
ing to severe political controversy and economic hardship13,14. The
annual cost of recovering Endangered Species Act-listed fish species
(more than US$800 million per year) now exceeds expenditures for
all other animal and plant groups combined15.
Water shortages have increased in both frequency and geographic
extent in the US and globally16,17. However, some recent water short-
ages have begun to stimulate policy responses. A severe drought in
California during 2012–2016 led to record levels of river and aquifer
depletion across the state and US$2.7 billion in agricultural losses in
2015 alone, provoking mandatory state-wide water use reductions
and legislation requiring preparation of sustainable groundwater-
management plans18,19. In recent decades, water extractions from
the Colorado River have exceeded total river flow, causing rapid
depletion of water-storage reservoirs (Fig. 1). In response, state and
federal water agencies are preparing demand-management plans to
stabilize reservoir levels and avoid mandatory reductions in water
deliveries to states sharing the basin’s water2022.
For water-management plans and policies to succeed, they need
sufficiently detailed and accurate information that can enrich under-
standing of the causes of water shortages and help guide decision
making around potential solutions. Here we assess river flow deple-
tion across the US, identify direct and indirect drivers of this deple-
tion, and assess options to reduce vulnerability to water shortages.
Our findings led to closer examination of the water use and eco-
logical impacts associated with irrigation of cattle-feed crops. We
Water scarcity and fish imperilment driven by
beef production
Brian D. Richter 1,2 ✉ , Dominique Bartak3, Peter Caldwell4, Kyle Frankel Davis 5,6,7,
Peter Debaere8, Arjen Y. Hoekstra 9,10, Tianshu Li 11, Landon Marston 12, Ryan McManamay 13,
Mesfin M. Mekonnen 14, Benjamin L. Ruddell15, Richard R. Rushforth15 and Tara J. Troy 16,17
Human consumption of freshwater is now approaching or surpassing the rate at which water sources are being naturally replen-
ished in many regions, creating water shortage risks for people and ecosystems. Here we assess the impact of human water
uses and their connection to water scarcity and ecological damage across the United States, identify primary causes of river
dewatering and explore ways to ameliorate them. We find irrigation of cattle-feed crops to be the greatest consumer of river
water in the western United States, implicating beef and dairy consumption as the leading driver of water shortages and fish
imperilment in the region. We assess opportunities for alleviating water scarcity by reducing cattle-feed production, finding
that temporary, rotational fallowing of irrigated feed crops can markedly reduce water shortage risks and improve ecological
sustainability. Long-term water security and river ecosystem health will ultimately require Americans to consume less beef that
depends on irrigated feed crops.
NATURE SUSTAINABILITY | VOL 3 | APRIL 2020 | 319–328 | 319
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... We built on the work of Richter et al. 3 by extending the hydrological simulation period from 1981 to 2019 and integrating new detailed monthly estimates of irrigation use for 30 individual crops (accounting for 94% of the total irrigated area and 95% of irrigation water consumption in the United States, Supplementary Table 1). We estimated monthly hydrological balances using the water supply stress index (WaSSI) ecosystem services model, which can simulate the hydrological impact of extractions from surface water and groundwater sources separately as well as hydrological interactions between river flow and groundwater 31,32 . ...
... We estimated monthly hydrological balances using the water supply stress index (WaSSI) ecosystem services model, which can simulate the hydrological impact of extractions from surface water and groundwater sources separately as well as hydrological interactions between river flow and groundwater 31,32 . Richter et al. 3 used static irrigation requirements based on annual average crop water requirements from 1996 to 2005. We have improved upon this approach by estimating crop water requirements at a monthly time step for each month from 1981 to 2019, which allowed us to capture the seasonal and interannual variability of crop water use, facilitating our assessment of trends and changing crop mixes over time. ...
... There are 2,099 HUC8 sub-basins in the conterminous United States, each with a mean area of 3,750 km 2 . All WaSSI input data and assumptions used in this study are exactly as described by Richter et al. 3 , but we included updated climate and land use data for an extended period of 1981-2019, as described below, and used substantially improved estimates of crop water consumption, also described below. An important feature of our hydrological model is the tracking of surface water flows from upstream to downstream sub-basins within each drainage network. ...
Irrigated agriculture dominates freshwater consumption globally, but crop production and farm revenues suffer when water supplies are insufficient to meet irrigation needs. In the United States, the mismatch between irrigation demand and freshwater availability has been exacerbated in recent decades due to recurrent droughts, climate change and overextraction that dries rivers and depletes aquifers. Yet, there has been no spatially detailed assessment of the potential for shifting to new crop mixes to reduce crop water demands and alleviate water shortage risks. In this study, we combined modelled crop water requirements and detailed agricultural statistics within a national hydrological model to quantify sub-basin-level river depletion, finding high-to-severe levels of irrigation scarcity in 30% of sub-basins in the western United States, with cattle-feed crops—alfalfa and other hay—being the largest water consumers in 57% of the region’s sub-basins. We also assessed recent trends in irrigation water consumption, crop production and revenue generation in six high-profile farming areas and found that in recent decades, water consumption has decreased in four of our study areas—a result of a reduction in the irrigated area and shifts in the production of the most water-consumptive crops—even while farm revenues increased. To examine the opportunities for crop shifting and fallowing to realize further reductions in water consumption, we performed optimizations on realistic scenarios for modifying crop mixes while sustaining or improving net farm profits, finding that additional water savings of 28–57% are possible across our study areas. These findings demonstrate strong opportunities for economic, food security and environmental co-benefits in irrigated agriculture and provide both hope and direction to regions struggling with water scarcity around the world.
... Our modeling effort builds upon the national WaSSI modeling effort described in Richter et al. (2020), which simulated river flow depletion for the 2000-2015 period. Because input data for Mexico had not been used in this previous WaSSI modeling effort, additional data on climate, topography, soils, and water use in Mexico needed to be acquired from other sources. ...
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The Rio Grande-Rio Bravo's flow regime has been highly altered for more than 130 years, yet the river ecosystem still supports important biodiversity including numerous endangered species. More than 80% of water consumed in the basin goes to irrigating farms, but in recent decades, farmers have repeatedly experienced severe water shortages. Given this water-scarce condition, any plans for enhancing environmental flows must be carefully designed to minimize impacts or provide benefits to agriculture. This study describes the development of the Rio Grande-Rio Bravo's first whole-basin hydrologic model-representing both the United States and Mexico portions of the basin-to enable exploration of environmental flow restoration needs and options for meeting these needs. We then demonstrate an analytical process in which environmental flow needs are compared to existing flow conditions to quantify gaps, and then evaluate how those gaps can be filled by reducing farm irrigation needs by shifting to less water-intensive crops and fallowing a portion of existing farmland while maintaining or improving net revenues. In our pilot assessment we find that an improvement of 2.2 m3/s would fill the environmental flow gap for late-summer low-flow conditions at Albuquerque, New Mexico. This flow enhancement is attainable by fallowing 18%-26% of cropland and shifting to more profitable and less water-intensive crops to sustain overall farm revenues.
... Across the United States, cities with high SCD values were less likely to experience food shocks of increasing intensity than cities with low SCD values ( Supplementary Fig. 2). While the exposure of cities' food supply chains to water stress did not vary considerably between food sectors, it did reveal a marked spatial pattern, characterized by cities in the west being more exposed to water stress than those in the east through food ows 30,31 (Supplementary Fig. 3). On average, across food sectors, the SCE of western cities was 0.50 versus 0.19 in eastern cities (p < 0.001). ...
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Global warming is exacerbating agricultural production losses from extreme climate events, with cascading impacts along supply chains that affect cities. However, little is known about cities’ vulnerability to climate-related food supply shocks. Here, using data-driven and network-based approaches, we determine the vulnerability of cities in the United States to domestic drought-related food shocks. Our vulnerability framework integrates key traits—resilience, exposure, and sensitivity to disruption—of a social-ecological system’s response to hazard. We find that vulnerability varies considerably across cities. It tends to be high for western cities because of both high supply chain exposure to water stress and high urban food insecurity. Using the 2012–2013 U.S. drought as a case study, we show that high-vulnerability cities are associated with more extreme food shocks and greater food supply losses than low-vulnerability cities. Our vulnerability framework can help inform climate adaptation interventions for food system security in urban-rural interactions.
... The TI data was derived from high-resolution global data [44]. The amount of surface or groundwater inputs that can impact on wetland distributions [45]. In this paper we use Euclidean distance to calculate surface drainage distance. ...
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Wetlands serve a critical function in water storage and ecological diversity maintenance. However, human activities have resulted in wetland loss in the middle and lower reaches of the Yangtze River Basin (MLYRB), while the wetland distribution in this area shows great discrepancy in previous estimates. It is, therefore, imperative to estimate the distribution of potential wetlands at present and project their variation under future climate change scenarios. In this study, we simulate the wetland distribution in the MLYRB at 15″ resolution using 5 machine learning methods with 19 predicting factors of topographic index, vegetation index, climate data, hydrological data, and soil type data. A 5-fold cross-validation with observed permanent wetlands shows that the reconstructions from Adaptive Boosting tree (AdaBoost) algorithm have the highest accuracy of 97.5%. The potential wetland area in the MLYRB is approximately ~1.25 × 105 km2, accounting for 15.66% of the study region. Direct human activities have led to the loss of nearly half of the potential wetlands. Furthermore, sensitivity experiments with the well-trained models are performed to quantify the response of the total wetland area to each influencing factor. Results indicate vulnerability of wetland areas to increases in leaf area index (LAI), coldest season temperature, warmest season temperature, and solar radiation. By the 2100s, the potential wetland area is expected to decrease by 40.5% and 50.6% under the intermediate and very high emissions scenarios, respectively. The changes in LAI and the coldest season temperature will contribute to 50% and 40% of this loss of potential wetlands, respectively. Wetland loss may further undermine biodiversity, such as waterfowl, and fail to provide functions such as flood protection, and water supply. This work reveals the spatial pattern of potential wetland areas and their sensitivity to climate changes, stressing the need for effective strategies to mitigate wetland loss at specific regions in the MLYRB.
... threats to human survival and the health of terrestrial and aquatic ecosystems [3][4][5][6]. In addition, urbanization, industrial development, and excessive use of pesticides have severely disrupted the natural equilibrium of the water ecosystem [7-9], thereby accelerating the depletion of available freshwater resources and promoting deterioration of water quality. ...
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Access to clean and equitable water is vital to human survival and an essential component of a sustainable society. Using 59 monitoring sections, the water quality of 32 rivers in 12 river systems within two river basins in one resource-depleted city (Jiaozuo) was examined in four seasons to better comprehend the extent of river pollution, and the distribution prediction of main indexes was conducted. In total, 92% of the monitoring sections met the national standards. Overall, 12.5%, 62.5%, and 25% of samples met water quality standards III, IV, and V, respectively. The concentrations of total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) ranged from 0.527 to 7.078, 0.001 to 1.789, and 0.53 to 799.25 mg/L, respectively. The Yellow River Basin has higher annual mean concentrations of total carbon (TC), TN, and total organic carbon (TOC) than the Haihe River Basin. The highest and lowest concentrations of specific water quality indices varied across seasons and rivers. Dashilao and Rongyou Rivers have the best water quality, while Dasha, Xin, and Mang Rivers have the worst. TN, TP, and NH4+-N concentrations in the Laomang River midstream were greater than those upstream and downstream. Statistically, significant positive associations were found between NH4+-N and TC, TOC, and COD (p < 0.025), where NH4+-N and COD influenced water quality the most. A significant positive relationship between COD and TP (p < 0.01) was observed. Overall, water quality values were highest in the summer and lowest in winter. The distribution prediction revealed TN, TP, NH4+-N, and COD showed significant regional differences. Household sewage, industrial sewage discharge, and agricultural contamination were all the possible significant contributors to declining water quality. These findings could provide a scientific reference for river water resource management in resource-depleted cities.
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Green algae Cladophora spp. inhabit waters with wide ranges of salinity and temperature, and their productivity is much higher than terrestrial plants. In natural waters, including hypersaline, they occupy large areas producing large biomass. Summing up and analyzing data from about 273 published articles, the review demonstrates the high production potential of Cladophora spp. and the diverse rich biochemical content of their biomass giving the prosperous possibility of their wide applications in agri–/aquaculture. As a fertilizer, they can be utilized by different methods (biochar, dry algae powder, etc.). Their extracts are effective growth stimulants for different cultivated plant species. Biomass is a promising fount of carbohydrates, vitamins, polyunsaturated fatty acids, proteins, essential microelements, and other biologically active compounds for the nutrition of animals and humans. Now their biomass is used in the feeding of livestock and chickens. It is also a valuable feed supplement for a variety of fish species, which may substitute up to 28% artificial feed in fish/shrimp cultivation. Cladophora co–farming with fish/shrimp reduces the use of artificial feed increasing commercial profitability. A wide use of Cladophora in agri–/aquaculture is economical and also mitigates environmental problems by reducing needs in agrarian land, and freshwater use, and likewise diminishing the emission of greenhouse gas methane by livestock.
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This study presents the assessment of water scarcity associated with livestock production in a watershed in Southern Brazil where 115 farms (poultry, pig, and milk) are located. The methods, AWARE—available water remaining, and BWSI—blue water scarcity index, were applied monthly for the year 2018, and the characterization factors (CF) were regionalized into five scenarios evaluated by varying water availability and environmental water requirements. Livestock water consumption accounted for 94.1% of the total water consumed. Low water scarcity was observed in all scenarios (BWSI < 0). The highest CFAWARE was observed in scenario 3, ranging from 2.15 to 9.70 m3 world eq.m3, with higher water scarcity in summer. In the same scenario, pig production presented the highest annual average water scarcity footprint (WSF) of 90.3 m3 world eq./t carcass weight. Among milk production systems, pasture-based systems presented the highest annual average WSF of 52.7 m3 world eq./t fat protein corrected milk, surpassing semi-confined and confined systems by 12.4% and 3.5%, respectively. In scenario 3, poultry production presented an annual average WSF of 49.3 m3 world eq./t carcass weight. This study contributes knowledge to the livestock sector to perform the assessment of water scarcity.
Plants sequester carbon through photosynthesis and provide primary productivity for the ecosystem. However, they also simultaneously consume water through transpiration, leading to a carbon-water balance relationship. Agricultural production can be regarded as a form of carbon sequestration behavior. From the perspective of the natural-social-economic complex ecosystem, excessive water usage in food production will aggravate regional water pressure for both domestic and industrial purposes. Hence, achieving a harmonious equilibrium between carbon and water resources during the food production process is a key scientific challenge for ensuring food security and sustainability. Digital intelligence (DI) and cyber-physical-social systems (CPSS) are emerging as the new research paradigms that are causing a substantial shift in the conventional thinking and methodologies across various scientific fields, including ecological science and sustainability studies. This paper outlines our recent efforts in using advanced technologies such as big data, artificial intelligence (AI), digital twins, metaverses, and parallel intelligence to model, analyze, and manage the intricate dynamics and equilibrium among plants, carbon, and water in arid and semiarid ecosystems. It introduces the concept of the carbon-water balance and explores its management at three levels: the individual plant level, the community level, and the natural-social-economic complex ecosystem level. Additionally, we elucidate the significance of agricultural foundation models as fundamental technologies within this context. A case analysis of water usage shows that, given the limited availability of water resources in the context of the carbon-water balance, regional collaboration and optimized allocation have the potential to enhance the utilization efficiency of water resources in the river basin. A suggested approach is to consider the river basin as a unified entity and coordinate the relationship between the upstream, midstream and downstream areas. Furthermore, establishing mechanisms for water resource transfer and trade among different industries can be instrumental in maximizing the benefits derived from water resources. Finally, we envisage a future of agriculture characterized by the integration of digital, robotic and biological farming techniques. This vision aims to incorporate small tasks, big models, and deep intelligence into the regular ecological practices of intelligent agriculture.
در چند دهه اخیر، سرانه تولید ناخالص داخلی (GDP) چین، هند و سایر اقتصادهای نوظهور به‌طور قابل توجهی افزایش یافته است. بر اساس گزارش بانک جهانی، سرانه تولید ناخالص داخلی چین و هند در سال 2017 به ترتیب ده و سه برابر بیشتر از 30 سال پیش است. در این زمینه، مجال کمی برای دیدگاه «محدودیت‌های رشد» وجود دارد که یادآور دهه 1970 و باشگاه رم در مورد بقیه جهان است . از آنجا که رشد اقتصادی این پتانسیل را دارد که تفاوت‌های درآمدی را در سطح بین‌المللی به حداقل برساند، اقتصادهای پیشرفته در موقعیتی نیستند که «محدودیت‌هایی برای رشد» بر بقیه جهان اعمال کنند. ازاین‌رو، یک راهکار احتمالی، رشد «خنثی از منابع»؛ یا در زمینه مورد مطالعه ما، رشد «خنثی از آب» است. به‌طور کلی، مصرف آب نمی‌تواند به افزایش ادامه دهد. باید محدودیتی برای مصرف کلی آب وجود داشته باشد و جوامع باید با آب کمتر کارهای بیشتری انجام دهند (کارایی بالاتری داشته باشند)، که بنا به ضرورت، افزایش بهره‌وری آب را به همراه دارد. درحالی‌که بهبود پایدار بهره‌وری آب ممکن است یک هدف عالی به نظر برسد، مهم است که تأکید شود که این یک موضوع کاملاً در دسترس می‌باشد.
Technical Report
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Water use in the United States in 2015 was estimated to be about 322 billion gallons per day (Bgal/d), which was 9 percent less than in 2010. The 2015 estimates put total withdrawals at the lowest level since before 1970, following the same overall trend of decreasing total withdrawals observed from 2005 to 2010. Freshwater withdrawals were 281 Bgal/d, or 87 percent of total withdrawals, and saline-water withdrawals were 41.0 Bgal/d, or 13 percent of total withdrawals. Fresh surface-water withdrawals (198 Bgal/d) were 14 percent less than in 2010, and fresh groundwater withdrawals (82.3 Bgal/day) were about 8 percent greater than in 2010. Saline surface-water withdrawals were 38.6 Bgal/d, or 14 percent less than in 2010. Total saline groundwater withdrawals in 2015 were 2.34 Bgal/d, mostly for mining use.
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Water for the Environment: From Policy and Science to Implementation and Management provides a holistic view of environmental water management, offering clear links across disciplines that allow water managers to face mounting challenges. The book highlights current challenges and potential solutions, helping define the future direction for environmental water management. In addition, it includes a significant review of current literature and state of knowledge, providing a one-stop resource for environmental water managers.
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The Tulare Basin in Central California is a site of intensive agricultural activity and extraction of groundwater, with pronounced ground subsidence and degradation of water resources over the past century. Spatially extensive observations of ground displacements from satellite-based remote sensing allow us to infer the response of the aquifer system to changes in usage and to marked recharge events such as the heavy winter rainfall in 2017. Radar imagery from the Sentinel-1a/b satellites (November 2014 to October 2017) illuminates secular and seasonal trends modulated by changes in withdrawal rates and the magnitude of winter precipitation. Despite the increased precipitation in early 2017 that led to a marked decrease, or in some areas, reversal, of subsidence rates, subsidence returned to rates observed during the drought within a matter of months.
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The United States is the largest producer of goods and services in the world. Rainfall, surface water supplies, and groundwater aquifers represent a fundamental input to economic production. Despite the importance of water resources to economic activity, we do not have consistent information on water use for specific locations and economic sectors. A national, spatially-detailed database of water use by sector would provide insight into US utilization and dependence on water resources for economic production. To this end, we calculate the water footprint of over 500 food, energy, mining, services, and manufacturing industries and goods produced in the US. To do this, we employ a data intensive approach that integrates water footprint and input-output techniques into a novel methodological framework. This approach enables us to present the most detailed and comprehensive water footprint analysis of any country to date. This study broadly contributes to our understanding of water in the US economy, enables supply chain managers to assess direct and indirect water dependencies, and provides opportunities to reduce water use through benchmarking. In fact, we find that 94% of US industries could reduce their total water footprint more by sourcing from more water-efficient suppliers in their supply chain than they could by converting their own operations to be more water-efficient.
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The availability of freshwater supplies to meet future demand is a growing concern. Water availability metrics are needed to inform future water development decisions. With the help of water managers, water availability was mapped for over 1300 watersheds throughout the 31 contiguous states in the eastern US complimenting a prior study of the west. The compiled set of water availability data is unique in that it considers multiple sources of water (fresh surface and groundwater, wastewater and brackish groundwater); accommodates institutional controls placed on water use; is accompanied by cost estimates to access, treat and convey each unique source of water; and is compared to projected future growth in consumptive water use to 2030. Although few administrative limits have been set on water availability in the east, water managers have identified 315 fresh surface water and 398 fresh groundwater basins (with 151 overlapping basins) as areas of concern (AOCs) where water supply challenges exist due to drought related concerns, environmental flows, groundwater overdraft, or salt water intrusion. This highlights a difference in management where AOCs are identified in the east which simply require additional permitting, while in the west strict administrative limits are established. Although the east is generally considered 'water rich' roughly a quarter of the basins were identified as AOCs; however, this is still in strong contrast to the west where 78% of the surface water basins are operating at or near their administrative limit. Little effort was noted on the part of eastern or western water managers to quantify non-fresh water resources.
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This study presents new data-driven, annual estimates of the division of precipitation into the recharge, quick-flow runoff, and evapotranspiration (ET) water budget components for 2000-2013 for the contiguous United States (CONUS). The algorithms used to produce these maps ensure water budget consistency over this broad spatial scale, with contributions from precipitation influx attributed to each component at 800 m resolution. The quick-flow runoff estimates for the contribution to the rapidly varying portion of the hydrograph are produced using data from 1,434 gaged watersheds, and depend on precipitation, soil saturated hydraulic conductivity, and surficial geology type. Evapotranspiration estimates are produced from a regression using water balance data from 679 gaged watersheds and depend on land cover, temperature, and precipitation. The quick-flow and ET estimates are combined to calculate recharge as the remainder of precipitation. The ET and recharge estimates are checked against independent field data, and the results show good agreement. Comparisons of recharge estimates with groundwater extraction data show that in 15% of the country, groundwater is being extracted at rates higher than the local recharge. These maps of the internally consistent water budget components of recharge, quick-flow runoff, and ET, being derived from and tested against data, are expected to provide reliable first-order estimates of these quantities across the CONUS, even where field measurements are sparse.
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As water scarcity worsens globally, there is growing interest in finding ways to reduce water consumption, and for reallocating water savings to other uses including environmental restoration. Because irrigated agriculture is responsible for more than 90% of all consumptive water use in water-scarce regions, much attention is being focused on opportunities to save water on irrigated farms. At the same time, many recent journal articles have expressed concern that claims of water-saving potential in irrigation systems lack technical credibility, or are at least exaggerated, due to failures to properly account for key elements of water budgets such as return flows. Critics have also asserted that opportunities for reallocating irrigation savings to other uses are limited because any freed up water is taken up by other farmers. A comprehensive literature and internet survey was undertaken to identify well-documented studies of water-saving strategies in irrigated agriculture, as well as case studies in which water savings have been successfully transferred to other uses. Our findings suggest that there is in fact considerable potential to reduce consumptive water use in irrigation systems when proper consideration is given to water budget accounting, and those savings can be beneficially reallocated to other purposes.
Data on urban water resources are scarce, despite a majority of the U.S. population residing in urban environments. Further, information on the energy required to facilitate the treatment, distribution, and collection of urban water is even more limited. In this study, we evaluate the energy-for-water component of the energy-water nexus by providing and analyzing a unique primary database consisting of drinking water and wastewater utility flows and energy. These anthropogenic fluxes of water through the urban environment are used to assess the state of the U.S. urban energy-water nexus at over 160 utilities. The average daily per person water flux is estimated at 560 liters of drinking water and 500 liters of wastewater. Drinking water and wastewater utilities require 340 kWh/1000 m3 and 430 kWh/1000 m3 of energy, respectively, to treat these resources. The total national energy demand for water utilities accounts for 1.0% of the total annual electricity consumption of the United States. Additionally, the water and embedded energy loss associated with non-revenue water accounts for 9.1 x 109 m3 of water and 3100 GWh, enough electricity to power 300,000 U.S. households annually. Finally, the water flux and embedded energy fluctuated monthly in many cities. As the nation's water resources become increasingly scarce and unpredictable, it is essential to have a set of empirical data for continuous evaluation and updates on the state of the U.S. urban energy-water nexus.
Between 2000 and 2014, annual Colorado River flows averaged 19% below the 1906-1999 average, the worst 15-year drought on record. At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.9°C above the 1906-99 average), confirming model-based analysis that continued warming will likely further reduce flows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend towards greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend. Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river flow, conservatively -20% by mid-century and -35% by end–century, with support for losses exceeding -30% at mid-century and -55% at end-century. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur. This article is protected by copyright. All rights reserved.