Colorado River Basin Water Supply And Demand Study
RECLAMATIONManaging Water in the WestColorado River BasinWater Supply and Demand StudyExecutive Summaryu.s. Department of the InteriorBureau of ReclamationDecember 2012
Mission StatementsThe U.S. Department of the Interior protects America’s natural resources and heritage,honors our cultures and tribal communities, and supplies the energy to power our future.The mission of the Bureau of Reclamation is to manage, develop, and protect water and relatedresources in an environmentally and economically sound manner in the interest of the American public.
Colorado River BasinWater Supply and Demand StudyExecutive SummaryU.S. Department of the InteriorBureau of ReclamationDecember 2012
Executive SummaryForewordThe Colorado River is the lifeblood of the southwestern United States.Stretching from the highest peaks of the Rocky Mountains to the Gulfof California, it travels over 1,400 miles across a watershed thatincludes seven states within the United States and two states in northern Mexico. Nearly 40million Americans rely on the Colorado River system for drinking water and to support liveli hoods ranging from farming to recreation. Emphasizing the economic, cultural, and ecologicsignificance of this river, our commitment to sound management for generations to come issteadfast. At the forefront of that pledge is the SECURE Water Act, the WaterSMART program,and Basin Studies across the West. These programs elevate water planning and management tonew levels with expanded science, collaboration, and forward thinking. Just as we benefit fromthe planning and works of prior generations, it is our obligation to use the best informationavailable to us to prepare for the water management challenges ahead.Conducted under the Basin Study Program, the Colorado River Basin Water Supply andDemand Study is the most comprehensive long-term assessment to date of the Colorado RiverBasin and its invaluable resources. Findings indicate that in the absence of timely action toensure sustainability, there exists a strong potential for significant imbalances between watersupply and demand in coming decades. Through the Study process, a common technical foun dation was established, upon which continued dialogue will be built towards actions that willenhance and preserve the future of communities, economies, and ecosystems supported by theColorado River.As the Basin copes with yet another year in an unprecedented drought extending back to 1999,the challenges of the task at hand are more real than ever. Though these challenges are unprece dented, I am confident that the partnerships forged and strengthened during this Study and overthe years will rise to meet the undertaking with vigor.Michael L. Connor,Commissioner, Bureau of Reclamation
Executive SummaryContents1.0Projected Future Water Supply and Demand Scenarios6Options and Strategies to Resolve Supply and DemandImbalances112.0Projected Future Water Supply and Demand Imbalances4.0Evaluation of Options and Strategies to Resolve Supplyand Demand Imbalances17Future Considerations and Next Steps263.05.06.0Study LimitationsDisclaimer92428
Executive SummaryFIGURE 1The Study Area - the hydrologic boundaries of the Basin within the United States, plus the adjacent areas ofthe Basin States that receive Colorado River water2
Executive SummaryExecutiveSummarySpanning parts of the seven states of Arizona,California, Colorado, New Mexico, Nevada,Utah, and Wyoming (Basin States), theColorado River Basin (Basin) is one of themost critical sources of water in the West. TheColorado River and its tributaries providewater to nearly 40 million people formunicipal use, supply water to irrigate nearly5.5 million acres of land, and is the lifebloodfor at least 22 federally recognized tribes(tribes), 7 National Wildlife Refuges, 4National Recreation Areas, and 11 NationalParks. Hydropower facilities along theColorado River provide more than 4,200megawatts of electrical generating capacity,helping to meet the power needs of the Westand offset the use of fossil fuels. TheColorado River is also vital to the UnitedMexican States (Mexico) to meet bothagricultural and municipal water needs.The Colorado River system is operated inaccordance with the Law of the River1.Apportioned water in the Basin exceeds theapproximate 100-year record (1906 through2011) Basin-wide average long-term historicalnatural flow2 of about 16.4 million acre-feet(maf). However, the Upper Basin States havenot fully developed use of their 7.5-mafapportionment, and total consumptive use3Lake Mead during drought conditionsand loss in the Basin has averagedapproximately 15.34 maf over the last 10years. Because of the Colorado Riversystem’s ability to store approximately 60maf, or nearly 4 years of average natural flowof the river, all requested deliveries were metin the Lower Basin despite recentlyexperiencing the worst 11-year drought in thelast century. However, there have beenperiodic shortages throughout the UpperBasin and the adjacent areas of the BasinStates that receive Colorado River water.1 The treaties, compacts, decrees, statutes, regulations, contracts and other legal documents and agreements applicable to theallocation, appropriation, development, exportation and management of the waters of the Colorado River Basin are oftencollectively referred to as the Law of the River. There is no single, universally agreed upon definition of the Law of the River, but itis useful as a shorthand reference to describe this longstanding and complex body of legal agreements governing the ColoradoRiver.2 Natural flow represents the flow that would have occurred at the location had depletions and reservoir regulation not beenpresent upstream of that location.3 Consumptive use is defined as water used, diminishing the available supply.4 Basin-wide consumptive use and losses estimated over the period 2002-2011, including the 1944 Treaty delivery to Mexico,reservoir evaporation, and other losses due to native vegetation and operational inefficiencies.3
Executive SummaryThe challenges and complexi ties of ensuring a sustainablewater supply and meetingfuture demand in an over-allocated and highlyvariable system such as the Colorado Riverhave been recognized and documented inThe Colorado River and itstributaries provide water to nearly40 million people for municipal use,supply water to irrigate nearly 5.5million acres of land, and is thelifeblood for at least 22 federallyrecognized tribes, 7 NationalWildlife Refuges, 4 NationalRecreation Areas, and 11 NationalParks.Green River in Utahseveral studies conducted by the Bureau ofReclamation (Reclamation) and the BasinStates over the past several decades. Lookingahead, concerns regarding the reliability ofthe Colorado River system to meet futureBasin resource5 needs are even moreapparent, given the likelihood of increasingdemand for water throughout the Basincoupled with projections of reduced supplydue to climate change.It was against this backdrop that the ColoradoRiver Basin Water Supply and Demand Study(Study) was conducted. Funded byReclamation through the Basin StudyProgram under the Department of theInterior’s WaterSMART (Sustain and ManageAmerica's Resources for Tomorrow) Programand the agencies6 representing the BasinStates, the Study was conducted byReclamation’s UpperColorado and LowerColorado Regions and therepresentatives of the BasinStates’ agencies. The pur pose of the Study was todefine current and futureimbalances in water supplyand demand in the Basinand the adjacent areas ofthe Basin States thatreceive Colorado Riverwater over the next 50years (through 2060), andto develop and analyzeadaptation and mitigationstrategies to resolve thoseimbalances. The Study didnot result in a decision as to5 Resources include water allocations and deliveries for municipal, industrial, and agricultural use; hydroelectric power generation;recreation; fish, wildlife, and their habitats (including candidate, threatened, and endangered species); water quality includingsalinity; flow- and water-dependent ecological systems; and flood control.6 The non-Federal cost-share partners are: Arizona Department of Water Resources, the (California) Six Agency Committee,Colorado Water Conservation Board, the New Mexico Interstate Stream Commission, the Southern Nevada Water Authority, theUtah Division of Water Resources, and the Wyoming State Engineer’s Office.4
Executive Summaryhow future imbalances should or will beaddressed. Rather, the Study provides a com mon technical foundation that frames therange of potential imbalances that may befaced in the future and the range of solutionsthat could be considered to resolve thoseimbalances.The Study Area is shown in figure 1 and isdefined as the hydrologic boundaries of theBasin within the United States, plus theadjacent areas of the Basin States that receiveColorado River water. In many adjacent areas,the Colorado River supply is in addition toother water supply sources used to meet waterdemands.The Study was conducted in collaborationwith stakeholders throughout the Basin.Interest in the Study was broad, and stake holders included tribes, agricultural users,purveyors of municipal and industrial (M&I)water, power users, and conservation andrecreation groups. Through extensive outreachefforts, the interested parties were engagedand their input was considered. This broadRecreation boating on Lake Powell in Utahparticipation and input wascritical to the Study.Because of the inherent complexities of theStudy and the many diverse interests andperspectives, eight interim reports andtechnical updates were published to reflecttechnical developments and the ongoing inputof stakeholders. The final documentation forthe Study is organized into three major parts:this Executive Summary, a Study Report, andseven Technical Reports. A compact disccontaining the Study documents in theirentirety can be found inside the back cover ofthe printed report.Project participants and stakeholders areencouraged to comment on the informationprovided in the Study Report and associatedTechnical Reports. Comments received beforeApril 19, 2013, will be summarized and post ed to the Study website and may informfuture planning activities in the Basin.Instructions for submitting comments are alsoprovided on the Study website .html.5
1.0 Projected Future WaterSupply and DemandScenariosThe amount of water available and changes inthe demand for water throughout the Basinover the next 50 years are highly uncertainand depend on a number of factors. Thepotential impacts of future climate changeand variability further contribute to theseuncertainties. Nevertheless, projections offuture water supply and demand were neededto assess the reliability of the Colorado Riversystem to meet Basin resource needs and toidentify options and strategies to mitigatefuture risks to those resources. To bebeneficial, these projections had to besufficiently broad to capture the plausibleranges of uncertainty in future water supplyand demand. A scenario planning process wasused to guide the development of scenariosthat provided a broad range of projections,resulting in four scenarios related to futurewater supply and six scenarios related tofuture water demand.1.1Water Supply ScenariosSince 2004, Reclamation has conducted a6multi-faceted research and developmentprograms to investigate and implement avariety of methods for projecting futurestreamflow for Colorado River planningstudies. Based on this work and theinformation gathered in the scenario planningprocess, four water supply scenarios werequantified and analyzed. These scenarios aretitled Observed Resampled, Paleo Resampled,Paleo Conditioned, and Downscaled GeneralCirculation Model (GCM) Projected and aredescribed as: Observed Resampled: Future hydrologictrends and variability are similar to thepast approximately100 years.Paleo Resampled: Future hydrologictrends and variability are represented byreconstructions of streamflow for a muchlonger period in the past (nearly 1,250years) that show expanded variability.Paleo Conditioned: Future hydrologictrends and variability are represented by ablend of the wet-dry states of the longerpaleo reconstructed period (nearly 1,250years), but magnitudes are more similar tothe observed period (about 100 years).
Projected Future Water Supply and Demand Scenarios Downscaled GCM Projected: Futureclimate will continue to warm withregional precipitation and temperaturetrends represented through an ensemble of112 future downscaled GCM projections.Under the Downscaled GCM Projectedscenario, the median of the mean natural flowat Lees Ferry over the next 50 years isprojected to decrease by approximately ninepercent, along with a projected increase inboth drought frequency and duration ascompared to the observed historical andpaleo-based scenarios. The range of this resultvaries amongst the individual GCMprojections that comprise this scenario withsome of the GCM projections showing alarger decrease in mean natural flow than ninepercent while others showing an increase overthe observed historical mean. Droughts7lasting 5 or more years are projected to occur50 percent of the time over the next 50 years.Projected changes in climate and hydrologicprocesses include continued warming acrossthe Basin, a trend towards drying (althoughprecipitation patterns continue to be spatiallyand temporally complex), increasedevapotranspiration, and decreased snowpackas a higher percentage of precipitation falls asrain, rather than snow and warmer tempera tures, causes earlier melt.The process of using GCM projections andhydrologic modeling to generate projectionsof future streamflow presents a number ofuncertainties and reflects methodologicalchoices made in the Study. For example,choices of different downscaling techniquesor the selection of a different hydrologicmodel to determine streamflow would yielddifferent results. Notwithstanding minormethodological and reporting differences, theresults presented in this report are consistentwith Reclamation’s report to Congresspublished in March 20118 in fulfillment of therequirements within Section (§) 9503 of theSECURE Water Subtitle of the OmnibusPublic Land Management Act of 2009 (PublicLaw 111-11).Lees Ferry, Colorado River, Arizona1.2Water Demand ScenariosHistorically, Reclamation has considered asingle projection of future demands in longterm Basin planning studies. The Studyconsidered a range of projections of demand,7 For the purpose of the Study, a drought period occurs whenever the running 2-year average flow at Lees Ferry falls below 15.0maf, the observed historical long-term mean.8 Bureau of Reclamation, 2011. SECURE Water Act Section 9503(c) – Reclamation Climate Change and Water 2011.7
Executive Summarydeveloped through a scenarioplanning process, which is asignificant and importantadvancement in long-term water planning inthe Basin. These demands were based on dataand information provided by the Basin States,tribes, federal agencies, and other waterentitlement holders. Through the scenarioplanning process, the most critical uncertain ties affecting future demand were identified(for example, changes in population and wateruse efficiency) and were combined into sixscenarios, as follows: Current Projected (A),Slow Growth (B), Rapid Growth (C1 and C2),and Enhanced Environment (D1 and D2).Agricultural irrigation in ArizonaBased on these scenarios, and factoring inboth Mexico’s 1944 Treaty allotment andwater loss due to evaporation and operations,the Colorado River demand for consumptiveThe Study considered a range ofprojections of demand, developedthrough a scenario planning process,which is a significant and importantadvancement in long-term waterplanning in the Basin.uses is projected to range between about 18.1maf under the Slow Growth (B) scenario andabout 20.4 maf under the Rapid Growth (C1)scenario by 2060. The largest increase indemand is projected to be in the M&I catego ry, due to population growth. Populationwithin the Study Area is projected to increasefrom about 40 million in 2015 to between49.3 million under the Slow Growth (B)scenario and 76.5 million under the RapidGrowth (C1) scenario by 2060. Additionally,the water demand assessment confirmed thatthe Lower Division States have demand forColorado River water beyond their 7.5 mafbasic apportionment across all scenarios.Non-consumptive9 demands, such as thoseassociated with uses for hydropower andrecreation and ecological resources, wereincluded through the development of systemreliability metrics and were not quantified inthe same manner as demand for consumptiveuses. For example, non-consumptive flowtargets supporting the environment andrecreational activities were developed forseveral locations throughout the Basin. Theimpact on these resources was assessed acrossall combinations of supply and demandscenarios in the Study’s system reliabilityanalysis.9 Non-consumptive use is defined as water used without diminishing available supply.8
2.0 Projected Future WaterSupply and DemandImbalancesThe range of the projected future water supplyand demand in the Basin, as determinedthrough the scenario process, is shownconceptually in figure 2. Without additionalfuture water management actions, a widerange of future imbalances is plausibleprimarily due to the uncertainty in futurewater supply. Comparing the median of watersupply projections against the median of thewater demand projections (medians areindicated by the darker shading), the longterm projected imbalance in future supply anddemand is about 3.2 maf by 2060. Theimbalance, however, can bemuch greater (or less) under anyone of the multiple plausiblefuture supply and demandscenarios. The projectedimbalance in figure 2 does notconsider the effect of reservoirstorage, which has and willcontinue to be used to meetBasin resource needs whendemand exceeds supply. Thepotential impacts associated withthese imbalances to Basinresources were assessed throughmodeling and use of system reli ability metrics, which considerthe effects of reservoir storage.Dry dock at Lake Mead in Nevada9
Executive SummaryFIGURE 2Historical Supply and Use1 and Projected Future Colorado River Basin Water Supply and Demand1 Water use and demand include Mexico’s allotment and losses such as those due to reservoir evaporation, native vegetation, andoperational inefficiencies.10
3.0 Options and Strategiesto Resolve Supply andDemand ImbalancesThe Basin States have made significantinvestments in developing other waterresources and implementing programs andpolicies to balance current and future supplieswith existing and future demands. Many ofthese efforts have resulted in solutions to pastwater management challenges and willcontinue to provide benefit to the system inmeeting the challenges that lie ahead.To identify a broad range of additionalpotential options to resolve water supply anddemand imbalances, input from Studyparticipants, interested stakeholders, and thegeneral public was solicited for considerationin the Study. The solicitation period was fromNovember 2011 through February 2012, andthose interested in submitting ideas wereasked to complete and submit an optionsubmittal form. During this period, over 150options were received and were organizedinto 4 groups: 1) those that increase Basinwater supply (Increase Supply), 2) those thatreduce Basin water demand (ReduceDemand), 3) those that focus on modifyingoperations (Modify Operations), and 4) thosethat focus primarily on Basin governance andmechanisms to facilitate option implementa tion (Governance and Implementation).Despite the submission of several options thatmay ultimately be considered too costly ortechnically infeasible, the Study exploreda wide range of options with the goal ofensuring that all viable options wereconsidered.From these broad groups, categories ofoptions were
Basin resource. 5 . needs are even more apparent, given the likelihood of increasing demand for water throughout the Basin coupled with projections of reduced supply due to climate change. It was against this backdrop that the Colorado River Basin Water Supply and Demand Study (Study) was
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the Ohio River Basin Water Resources Initiative . The goals of this report is to provide a quantifiable estimate of water lost via interbasin transfers, the regulatory policies in place, the role of agencies / . Water Resources Council, Susquehanna River Basin Commission, Interstate Commission on the Potomac River Basin, Apalachicola .
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Apportioned Colorado River water is widely acknowledged to be in excess of the river's natural flows, and consumptive use of these waters typically exceeds natural flows. This causes an imbalance in the basin's available water supply and demand. Stress on basin water supplies is exacerbated by a long-term drought dating to 2000.
Susquehanna River Basin Commission (SRBC) -enhance public welfare through comprehensive planning, water supply allocation, and management of the water resources of the basin -monitoring, planning, regulatory (allocation) Delaware River Basin Commission (DRBC) -for the conservation, utilization, development, management, and control
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portant from context of the Upper Blue Nile (UBN) Basin for two reasons. First, the UBN Basin is the major water source area of the Nile River, as it contributes around 70% of the overall Nile flow. Thus, the UBN Basin is the most impor-tant river basin not only for Ethiopia but also for the down-stream Nile Basin countries (i.e. Sudan and Egypt).
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