U.S. Department of the Interior 

Bureau of Reclamation December 2012 

Colorado River Basin 

Water Supply and Demand Study 

Executive Summary – Pre-Production Copy 

U.S. Department of the Interior 

Bureau of Reclamation December 2012 

Colorado River Basin 

Water Supply and Demand Study 

Executive Summary – Pre-Production Copy 

EXECUTIVE SUMMARY ES-1 DECEMBER 2012

PRE-PRODUCTION COPY

Executive Summary

Spanning parts of the seven states of Arizona, California, Colorado, New Mexico, Nevada, 

Utah, and Wyoming (Basin States), the Colorado River Basin (Basin) is one of the most 

critical sources of water in the West. The Colorado River and its tributaries provide water to 

nearly 40 million people for municipal use, supply water used to irrigate nearly 5.5 million 

acres of land, and is also the lifeblood for at least 22 federally recognized tribes (tribes), 

7 National Wildlife Refuges, 4 National Recreation Areas, and 11 National Parks. 

Hydropower facilities along the Colorado River provide more than 4,200 megawatts of 

generating capacity, helping to meet the power needs of the West and offset the use of fossil 

fuels. The Colorado River is also vital to the United Mexican States (Mexico) to meet both

agricultural and municipal water needs.

The Colorado River system is operated in accordance with the Law of the River1. 

Apportioned water in the Basin exceeds the approximate 100-year record (1906 through 

2011) Basin-wide average long-term historical natural flow2 of about 16.4 million acre-feet 

(maf). However, the Upper Basin States have not fully developed use of their 7.5-maf

apportionment, and total consumptive use3 and losses in the Basin has averaged 

approximately 15.34

The challenges and complexities of ensuring a sustainable water supply and meeting future 

demand in an over-allocated and highly variable system such as the Colorado River have 

been recognized and documented in several studies conducted by the Bureau of Reclamation 

(Reclamation) and the Basin States over the past several decades. Looking ahead, concerns 

regarding the reliability of the Colorado River system to meet future Basin resource

maf over the last 10 years. Because of the Colorado River system’s 

ability to store approximately 60 maf, or nearly 4 years of average natural flow of the river, 

all requested deliveries were met in the Lower Basin despite recently experiencing the worst 

11-year drought in the last century. However, there have been periodic shortages throughout 

the Upper Basin and the adjacent areas of the Basin States that receive Colorado River water. 

5

It was against this backdrop that the Colorado River Basin Water Supply and Demand Study 

(Study) was conducted. Funded by the Reclamation through the Basin Study Program under 

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. 

 

1 The treaties, compacts, decrees, statutes, regulations, contracts and other legal documents and agreements applicable to 

the allocation, appropriation, development, exportation and management of the waters of the Colorado River Basin are often 

collectively referred to as the Law of the River. There is no single, universally agreed upon definition of the Law of the River, 

but it is useful as a shorthand reference to describe this longstanding and complex body of legal agreements governing the 

Colorado River.

2 Natural flow represents the flow that would have occurred at the location had depletions and reservoir regulation not been 

present 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.

5 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 

including salinity; flow- and water-dependent ecological systems; and flood control.
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the Department of the Interior’s WaterSMART (Sustain and Manage America's Resources 

for Tomorrow) Program and the agencies6

The Study Area is shown in figure 1 and is defined as the hydrologic boundaries of the Basin 

within the United States, plus the adjacent areas of the Basin States that receive Colorado 

River water. In many adjacent areas, the Colorado River supply is in addition to other water 

supply sources used to meet water demands. 

representing the Basin States, the Study was

conducted by Reclamation’s Upper Colorado and Lower Colorado Regions and the 

representatives of the Basin States’ agencies. The purpose of the Study was to define current 

and future imbalances in water supply and demand in the Basin and the adjacent areas of the 

Basin States that receive Colorado River water over the next 50 years (through 2060), and to 

develop and analyze adaptation and mitigation strategies to resolve those imbalances. The 

Study did not result in a decision as to how future imbalances should or will be addressed. 

Rather, the Study provides a common technical foundation that frames the range of potential 

imbalances that may be faced in the future and the range of solutions that may be considered 

to resolve those imbalances. 

 

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, 

the Utah Division of Water Resources, and the Wyoming State Engineer’s Office.
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FIGURE 1 

The Study Area
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The Study was conducted in collaboration with stakeholders throughout the Basin. Interest in 

the Study was broad, and stakeholders included tribes, agricultural users, purveyors of 

municipal and industrial (M&I) water, power users, and conservation and recreation groups. 

Through outreach efforts, these interested parties were engaged and their input was 

considered. This broad participation and input was critical to the Study.

Because of the inherent complexities of the Study and the many diverse interests and 

perspectives, interim reports and technical updates were published to reflect technical 

developments and the ongoing input of stakeholders. Throughout the course of the Study, 

eight of these interim products were published. The final documentation for the Study is 

organized into three major parts: this Executive Summary, a Study Report, and seven

Technical Reports.

Project participants and stakeholders are encouraged to comment on the information 

provided in the final Study Report and associated Technical Reports. Written comments 

should be submitted within 90 days following the release of this report. The comments will 

be summarized and posted to the Study website, and may inform future planning activities in 

the Basin. Instructions for submitting comments are also provided on the Study website at: 

http://www.usbr.gov/lc/region/programs/crbstudy.html

1.0 Projected Future Water Supply and Demand

Scenarios 

The amount of water available and changes in the demand for water throughout the Basin 

over the next 50 years are highly uncertain and depend on a number of factors. The potential 

impacts of future climate change and variability further contribute to these uncertainties. 

Nevertheless, projections of future water supply and demand were needed to assess the 

reliability of the Colorado River system to meet Basin resource needs and to identify options 

and strategies to mitigate future risks to those resources. To be beneficial, these projections 

must be sufficiently broad to capture the plausible ranges of uncertainty in future water 

supply and demand. A scenario planning process was used to guide the development of 

scenarios that provided a broad range of projections, resulting in four scenarios related to 

future water supply and six scenarios related to future water demand. 

1.1 Water Supply Scenarios

Since 2004, Reclamation has conducted a multi-faceted research and development programs 

to investigate and implement a variety of methods for projecting future streamflow for 

Colorado River planning studies. Based on this work and the information gathered in the 

scenario planning process, four water supply scenarios were quantified and analyzed. These 

scenarios are titled Observed Resampled, Paleo Resampled, Paleo Conditioned, and 

Downscaled General Circulation Model (GCM) Projected and are described as: 

• Observed Resampled: Future hydrologic trends and variability are similar to the past 

approximately100 years.

• Paleo Resampled: Future hydrologic trends and variability are represented by 

reconstructions of streamflow for a much longer period in the past (nearly 1,250 years) 

that show expanded variability. 
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• Paleo Conditioned: Future hydrologic trends and variability are represented by a blend 

of the wet-dry states of the longer paleo reconstructed period (nearly 1,250 years), but 

magnitudes are more similar to the observed period (about 100 years).

• Downscaled GCM Projected: Future climate will continue to warm with regional 

precipitation and temperature trends represented through an ensemble of 112 future 

downscaled GCM projections. 

Under the Downscaled GCM Projected scenario, the mean natural flow at Lees Ferry over 

the next 50 years is projected to decrease by approximately 9 percent, along with a projected 

increase in both drought frequency and duration as compared to the observed historical and 

paleo-based scenarios. The range of this result varies amongst the individual GCM 

projections that comprise this scenario with some of the GCM projections showing a larger 

decrease in mean natural flow than 9 percent while others showing an increase over the 

observed historical mean. Droughts7

The process of using GCM projections and hydrologic modeling to generate projections of 

future streamflow presents a number of uncertainties and reflects methodological choices 

made in the Study. For example, choices of different downscaling techniques or the selection 

of a different hydrologic model to determine streamflow would yield different results. 

Notwithstanding minor methodological and reporting differences, the results presented in this 

report are consistent with Reclamation’s report to Congress published in March 2011

lasting 5 or more years are projected to occur 50 percent 

of the time over the next 50 years. Projected changes in climate and hydrologic processes

include continued warming across the Basin, a trend towards drying (although precipitation 

patterns continue to be spatially and temporally complex) increased evapotranspiration and 

decreased snowpack as a higher percentage of precipitation falls as rain rather than snow and 

warmer temperatures cause earlier melt. 

8

1.2 Water Demand Scenarios

in

fulfillment of the requirements within Section (§) 9503 of the SECURE Water Subtitle of the 

Omnibus Public Land Management Act of 2009 (Public Law 111-11). 

Historically, Reclamation has considered a single projection of future demands in long-term 

Basin planning studies. The Study considered a range of projections of demand, developed 

through a scenario planning process, which is a significant and important advancement in 

long-term water planning in the Basin. These demands were based on data and information 

provided by the Basin States, tribes, federal agencies, and other water entitlement holders. 

Through the scenario planning process, the most critical uncertainties affecting future 

demand were identified (for example, changes in population and water use efficiency) and 

were combined into six scenarios, as follows: Current Projected (A), Slow Growth (B), Rapid 

Growth (C1 and C2), and Enhanced Environment (D1 and D2). 

Based on these scenarios, and factoring in both Mexico’s allotment and water loss due to 

evaporation and operations, the Colorado River demand for consumptive uses is projected to 

range between about 18.1 maf under the Slow Growth (B) scenario and about 20.4 maf under 

 

7 For the purpose of the Study, a drought period occurs whenever the running 2-year average flow at Lees Ferry falls below 

15.0 maf, the observed historical long-term mean.

8 Bureau of Reclamation, 2011. SECURE Water Act Section 9503(c) – Reclamation Climate Change and Water 2011. 
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the Rapid Growth (C1) scenario by 2060. The largest increase in demand is projected to be in 

the M&I category, owing to population growth. Population within the Study Area is 

projected to grow from about 40 million in 2015 to between 49.3 million under the Slow 

Growth (B) scenario and 76.5 million under the Rapid Growth (C1) scenario by 2060. 

Additionally, the water demand assessment confirmed that the Lower Division States have 

demand for Colorado River water beyond their 7.5 maf basic apportionment across all 

scenarios.

Non-consumptive9

2.0 Projected Future Water Supply and Demand 

Imbalances 

 demands, such as those associated with uses for hydropower and

recreation and ecological resources, were included through the development of system 

reliability metrics and were not quantified in the same manner as demand for consumptive 

uses. For example, non-consumptive flow targets supporting the environment and 

recreational activities were developed for several locations throughout the Basin. The impact 

on these resources was assessed across all combinations of supply and demand scenarios in 

the Study’s system reliability analysis.

The range of the projected future water supply and demand in the Basin, as determined 

through the scenario process, is shown conceptually in figure 2. Without additional future 

water management actions, a wide range of future imbalances is plausible, primarily due to 

the uncertainty in future water supply. Comparing the median of water supply projections 

against the median of the water demand projections (medians are indicated by the darker 

shading), the long-term projected imbalance in future supply and demand is about 3.2 maf by 

2060. The imbalance, however, can be much greater (or less) under any one of the multiple 

plausible future supply and demand scenarios. The projected imbalance in figure 2 does not 

consider the effect of reservoir storage, which has and will continue to be used to meet Basin 

resource needs when demand exceeds supply. Through modeling and the use of system 

reliability metrics, which consider the effects of reservoir storage, the potential impacts 

associated with these imbalances to Basin resources were assessed. 

 

9 Non-consumptive use is defined as water used without diminishing available supply.
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FIGURE 2 

Historical Supply and Use1 and Projected Future Colorado River Basin Water Supply and Demand1

1Water use and demand include Mexico’s allotment and losses such as those due to reservoir evaporation, native vegetation, 

and operational inefficiencies.

3.0 Options and Strategies to Resolve Supply and 

Demand Imbalances

The Basin States have made significant investments in developing other water resources and 

implementing programs and policies to balance current and future supplies with existing and 

future demands. Many of these efforts have resulted in solutions to past water management 

challenges and will continue to provide benefit to the system in meeting the challenges that 

lie ahead. 

To identify a broad range of additional potential options to resolve water supply and demand 

imbalances, input from Study participants, interested stakeholders, and the general public 

was solicited for consideration in the Study. The solicitation period was from November 

2011 through February 2012, and those interested in submitting ideas were asked to complete 

and submit an option submittal form. During this period, over 150 options were received and 

were organized into 4 groups: 1) those that increase Basin water supply (Increase Supply), 

2) those that reduce Basin water demand (Reduce Demand), 3) those that focus on modifying 

operations (Modify Operations), and 4) those that focus primarily on Basin governance and 

mechanisms to facilitate option implementation (Governance and Implementation). Despite 

the submission of several options that may ultimately be considered too costly or technically 

infeasible, the Study explored a wide range of options with the goal of ensuring that all 

viable options were considered. 

From these broad groups, categories of options were developed, and each submitted option 

was assigned to one category based on its primary function. Recognizing that every option 
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submitted could not undergo further evaluation due to time and resource constraints, 

representative options that spanned the range of the option categories were developed. About 

30 representative options were developed to ensure the concepts embodied in each submitted 

option were reflected and were further evaluated. Many of the representative options were 

evaluated quantitatively, which entailed an assessment of cost, yield, and timing in addition 

to assignment of a rating (“A” through “E”) to 14 other criteria, listed in table 1. 

TABLE 1

Criteria Used to Evaluate Representative Options

Technical Environmental 

Technical Feasibility

Implementation Risks

Long-Term Viability 

Operational Flexibility

Permitting 

Energy Needs

Energy Source

Other Environmental Factors

Social Other

Recreation

Policy

Legal

Socioeconomics

Quantity of Yield

Timing

Cost 

Hydropower

Water Quality

Whereas many of the criteria were assigned a qualitative rating, the assessment of cost, 

quantity of yield, and timing entailed numeric estimates to facilitate the grouping of these 

options into portfolios and the modeling of those portfolios. Costs were computed as present 

day annualized capital, operating, and replacement cost per acre-foot of option yield. It 

should be noted that the assessment of these criteria was at an appraisal level and there are 

many associated uncertainties, especially with respect to estimates regarding costs and 

quantity of yield. For representative options for which the criteria listed in table 1 was not 

suitable, such as those options in the Governance and Implementation group, a qualitative 

description was provided. A summary of the representative options within the Increase 

Supply, Reduce Demand, and Modify Operations groups and the cost, yield, and timing, and 

inclusion in portfolios, where applicable, is provided in table 2. 

The Governance and Implementation group consists of ideas and suggestions related to three 

major categories: Water Management and Allocation, Tribal Water, and Data and 

Information. Most concepts related to Water Management and Allocation and Tribal Water 

have significant legal and policy considerations and were included in the Study but were not 

assessed. Where appropriate, these concepts will require future discussions beyond the scope 

of the Study. Data and Information ideas recommended future data and tool development to 

support future planning activities in the Basin. 
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TABLE 2

Summary of Representative Options Including Cost, Timing, Potential Yield, and Inclusion in Portfolios

Option 

Type

Option 

Category

Representative 

Option

Estimated 

Cost

($/afy)

Years 

before 

Available

Potential 

Yield by 

2035 (afy)

Potential 

Yield by 

2060 

(afy)

Option 

Included in 

Portfolio

Increase 

Supply

Desalination Gulf of California 2,100 20 – 30 200,000 1,200,000 Portfolios A, 

B (up to 

400 kafy)

Pacific Ocean in 

California

1,850–

2,1001

20–25 200,000 600,000 Portfolios A, 

B (up to 

400 kafy)

Pacific Ocean in 

Mexico

1,500 15 56,000 56,000 Portfolios A, 

B 

Salton Sea 

Drainwater

1,000 15–25 200,000 500,000 All Portfolios

Groundwater in 

Southern 

California

750 10 20,000 20,000 All Portfolios

Groundwater in 

the Area near 

Yuma, Arizona

600 10 100,000 100,000 All Portfolios

Subtotal 776,000 2,476,000

Reuse Municipal 

Wastewater

1,500–

1,800

10–35 200,000 932,000 All Portfolios

Grey Water 4,200 10 178,000 178,000 Portfolio C

Industrial 

Wastewater

2,000 10 40,000 40,000 All Portfolios

Subtotal 418,000 1,150,000

Local Supply Treatment of 

Coal Bed 

MethaneProduced Water

2,000 10 100,000 100,000 Portfolios A, 

B 

Rainwater 

Harvesting

3,150 5 75,000 75,000 Portfolio C

Subtotal 175,000 175,000

Watershed 

Management

Brush Control 7,500 15 50,000 50,000 None

Dust Control 220–520 15–25 280,000 400,000 Portfolios A, 

C 

Forest 

Management

500 20–30 200,000 300,000 None

Tamarisk Control 400 15 30,000 30,000 Portfolios A, 

C 

Weather 

Modification

30–60 5–45 700,000 1,700,000 All Portfolios 

(up to 

300 kafy)

Subtotal 1,260,000 2,480,000
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TABLE 2

Summary of Representative Options Including Cost, Timing, Potential Yield, and Inclusion in Portfolios

Option 

Type

Option 

Category

Representative 

Option

Estimated 

Cost

($/afy)

Years 

before 

Available

Potential 

Yield by 

2035 (afy)

Potential 

Yield by 

2060 

(afy)

Option 

Included in 

Portfolio

Increase 

Supply

Importation Imports to the 

Colorado Front 

Range from the 

Missouri or 

Mississippi 

Rivers

1,700–

2,300

30 0 600,000 Portfolios A, 

B

Imports to the 

Green River from 

the Bear, Snake1

or Yellowstone 

Rivers

700–1,900 15 158,000 158,000 None

Imports to 

Southern 

California via 

Icebergs, 

Waterbags, 

Tankers, or from 

the Columbia 

River1

2,700–

3,400

15 600,000 600,000 None

Subtotal 758,000 1,358,000

Reduce 

Demand

M&I Water 

Conservation

M&I Water 

Conservation

500–900 5–40 600,000 1,000,000 All Portfolios

Subtotal 600,000 1,000,000

Agricultural 

Water 

Conservation

Agricultural 

Water 

Conservation

150–750 10–15 1,000,000 1,000,000 All Portfolios

Agricultural 

Water 

Conservation 

with Transfers 

250–750 5–15 1,000,000 1,000,000 All Portfolios

Subtotal 1,000,0002 1,000,0002

Energy 

Water Use 

Efficiency

Power Plant 

Conversion to Air 

Cooling

2,000 10 160,000 160,000 All Portfolios

Subtotal 160,000 160,000

Modify 

Operations

System 

Operations

Evaporation 

Control via Canal 

Covers

15,000 10 18,000 18,000 None

Evaporation 

Control via 

Reservoir 

Covers

15,000 20 200,000 200,000 None

Evaporation 

Control via 

Chemical Covers 

on Canals or 

Reservoirs

100 15–25 200,000 850,000 None
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TABLE 2

Summary of Representative Options Including Cost, Timing, Potential Yield, and Inclusion in Portfolios

Option 

Type

Option 

Category

Representative 

Option

Estimated 

Cost

($/afy)

Years 

before 

Available

Potential 

Yield by 

2035 (afy)

Potential 

Yield by 

2060 

(afy)

Option 

Included in 

Portfolio

Modified 

Reservoir 

Operations

N/A 15 0–300,000 0–300,000 None

Construction of 

New Storage

2,250 15 20,000 20,000 None

Subtotal 588,0003 1,238,0003

Water 

Transfers, 

Exchanges, 

and Banking

Water Transfers 

and Exchanges 

(same as 

Agricultural 

Water 

Conservation 

with Transfers)

250–750 5–15 1,000,000 1,000,000 All Portfolios

Upper Basin 

Water Banking4

NN/A A Assu10 500,000 800,000 Portfolios 

A,C

All Options 5,735,0005 11,037,000

5

1

Among the more than 150 options submitted to Reclamation as responsive to the Plan of Study, additional importation of 

water supplies from various sources, including importation of water from the Snake and Columbia River systems, were 

submitted to the Study. Such options were appropriately reflected in the Study but did not undergo additional analysis as part 

of a regional or river basin plan or any plan for a specific Federal water resource project. This Study is not a regional or river 

basin plan or proposal or plan for any Federal water resource project

2 The two agricultural water conservation representative options derive potential yield from similar measures and are thus not 

additive

3 Subtotal assumes 150,000 afy for the Modified Reservoir Operations representative option. 

4 The values related to Upper Basin Banking reflected assumptions developed for modeling purposes. It was assumed that 

bank water is generated through conservation; therefore, the potential yield of the bank is consistent with the Upper Basin 

portion of agricultural and M&I conservation and energy water use efficiency

5 Total does not account for several options that may be mutually exclusive due to regional integration limitations or are 

dependent on the same supply. 

When considering all options and all categories, the potential yield is approximately 5.7 maf 

per year (mafy) by 2035 and more than 11 mafy by 2060. However, not all options are 

equally feasible or reliable in the long term. Some options, such as imports into southern 

California via submarine pipelines, water bags, icebergs, or those related to watershed 

management (e.g. weather modification or dust control), have either significant technical 

feasibility challenges or significant questions regarding their reliability. Excluding options 

that rate low for these factors, the potential yield is reduced to approximately 3.7 mafy by 

2035 and to approximately 7 mafy by 2060. 

Recognizing no single option will be sufficient to resolve future projected supply and 

demand imbalances, groups of options, or portfolios, were developed to reflect different 

adaptive strategies. Each portfolio consists of a unique combination of options that were 

considered to address Basin resource needs—for example, the water elevation in Lake 

Mead— that may exist under future combinations of supply and demand. Four portfolios 

were evaluated in the Study and represent a range of reasonable but different approaches for 
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resolving future supply and demand imbalances. The portfolios are not intended to represent 

all possible strategies for grouping options. Further, the Study does not result in the selection 

of a particular portfolio or any one option from any portfolio. The objective of the portfolio 

analyses is to demonstrate the effectiveness of different strategies in resolving future supply 

and demand imbalances.

Using the ratings associated with the criteria listed in table 1 to express certain preferences

towards a future strategy, resulted in two portfolios, Portfolio B and Portfolio C. Two other 

portfolios were then developed, Portfolio A and Portfolio D, to represent a highly inclusive 

strategy (includes all options in either Portfolio B or Portfolio C) and a highly selective 

strategy (includes only options in both Portfolio B and Portfolio C). The four portfolios 

considered in the Study are summarized in table 3. 

Portfolio B is based on a strategy that seeks long-term water supply reliability through 

implementation of options with high technical feasibility and long-term reliability. The 

strategy can be defined as seeking options with proven technology that, once in place, will 

produce reliable long-term yield. The strategy represents a low-risk strategy in the long term, 

but allows greater risk with respect to permitting and implementation.

Portfolio C focuses on options that are technically feasible but also may have lower 

environmental impacts—low energy needs, lower carbon energy sources, low permitting 

risk, and low impacts to other environmental factors. The strategy can be defined as one that 

prioritizes options providing long-term solutions that are flexible and seek to enhance 

ecological and recreational flows while minimizing the effects on other Basin resources. The 

strategy represents a low-risk strategy in the near term but allows greater risk with respect to 

long-term performance of conservation measures.

TABLE 3 

Study Portfolios

Portfolio Name Portfolio Description 

Portfolio A Is the least restrictive and contains all options that are in both Portfolio B and Portfolio C. 

Portfolio B Includes options with high technical feasibility and high long-term reliability; excludes 

options with high permitting, legal, or policy risks. 

Portfolio C Includes only options with relatively low energy intensity; includes an option that results in 

increased instream flows; excludes options that have low feasibility or high permitting risk. 

Portfolio D Is the most selective and contains only those options that are included in both Portfolio B

and Portfolio C. 

4.0 Evaluation of Opportunities to Resolve Supply and 

Demand Imbalances

The evaluation of the effectiveness of the four portfolios at resolving future potential supply 

and demand imbalances consisted of the following: identifying the reliability of the system at 

meeting Basin resource needs under all future supply and demand scenarios without 

portfolios in place (termed “Baseline” system reliability); defining of vulnerable 

conditions—those stressing to Basin resources; and evaluating the effectiveness of portfolios 

as measured by their ability to improve system reliability and reduce vulnerabilities relative 
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to the Baseline. The estimation of cost and other tradeoffs associated with implementing the 

four portfolios was also explored. 

The performance of Basin resources was measured through system reliability metrics 

(metrics). With broad stakeholder involvement, a comprehensive set of metrics that span six 

resource categories (Water Delivery, Electrical Power, Water Quality, Flood Control, 

Recreational, and Ecological Resources) was identified. From those metrics, levels reflecting 

vulnerability or resource risk were identified. The combination of a particular metric and the 

assumed level of risk are termed “vulnerability.” Two important vulnerabilities that provide 

an overall indication of system reliability are: 1) Lake Mead elevation dropping below 1,000 

feet above mean sea level (msl) in any month and 2) Lee Ferry deficit10

Baseline system reliability was modeled considering all combinations of the supply and 

demand scenarios. Additionally, two operational assumptions regarding Lake Powell and 

Lake Mead operations past the effective period of the Colorado River Interim Guidelines for 

Lower Basin Shortages and Coordinated Operation for Lake Powell and Lake Mead in 2026 

were considered. Since each supply scenario has over 100 individual sequences, the Baseline 

system reliability is comprised of over 20,000 simulations. Despite the findings from the 

water demand assessment that the Lower Division States have demand for Colorado River 

water beyond their 7.5 maf basic apportionment, the Baseline system reliability assumes 

deliveries to the Lower Division States remain consistent with and within their basic 

apportionment. 

, when the 10-year 

running total flow at Lee Ferry, Arizona is less than 75 maf. 

In summary, the Baseline analysis indicates that without action, it will become increasingly 

difficult for the system to meet Basin resource needs over the next 50 years. Future projected 

development of water supplies and increased consumptive use in the Upper Basin combined 

with potential reductions in future supply results in reduced volumes of water stored in 

system reservoirs. With lower water elevations in reservoirs, the needs for resources such as 

hydropower and shoreline recreation were less frequently satisfied, while water delivery 

shortages increased. Decreases in flows in key river tributaries have negative implications 

for flow-dependent resources such as boating recreation and river ecology. These findings 

fully support the need to develop and evaluate options and strategies to help resolve the water 

supply and demand imbalance. Vulnerabilities for the latter period of the Study period (2041 

through 2060) under Baseline conditions are summarized in table 4. 

The Baseline system reliability also reveals that many combinations of future water supply 

and demand result in management challenges. In fact, most combinations stress some Basin 

resources through 2060. In the near-term (2012 through 2026), water demands are similar 

across scenarios, and the largest factor affecting the system reliability is water supply. In the 

mid-term (2027 through 2040), the demand for water is an increasingly important element in 

the reliability of the system, as are assumptions regarding the operations of Lakes Powell and 

Mead. In the long-term (2041 through 2060), the futures that consider the Downscaled GCM 

Projected water supply scenario, which incorporates projections of future climate, show a 

high inability to meet resource needs, regardless of the demand scenario and the operation of 

 

10 Article III(d) of the Colorado River Compact stipulates that the Upper Division States will not cause the flow of the river at 

the Lee Ferry Compact Point to be depleted below an aggregate of 75 maf for any period of 10 consecutive years. For the 

purpose of the Study, a Lee Ferry deficit is defined as the difference between 75 maf and the 10-year total flow arriving at Lee 

Ferry.
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Lakes Powell and Mead. The first stage in the portfolio analysis revealed that when all 

options in the most inclusive portfolio (Portfolio A) are implemented immediately upon 

availability, and without meeting demand of the Lower Division States above 7.5 maf, 

plausible futures still exist in which the system is vulnerable. While the implementation of 

these options results in a sizeable reduction in vulnerability (the percentage of futures 

resulting in Lake Mead elevations being less than 1,000 feet msl is reduced from about 19 

percent to 3 percent), these results indicate that complete elimination of Basin vulnerability is 

not likely attainable. 

Because the Lower Division States have demand for Colorado River water above their 

7.5 maf basic apportionment, any Basin-wide strategy must take this into consideration. As 

such, the portfolio analysis was designed to not only implement options to reduce system 

vulnerability but also to satisfy the Lower Division States’ demand above the 7.5 maf basic

apportionment. Augmentation, reuse, and conservation (with and without transfers) were the 

only options included in the portfolio analysis that could be used to satisfy these demands. 

A summary of the system reliability results with the four portfolios in place is also 

summarized in table 4. Each portfolio was modeled under all future conditions that 

comprised the Baseline reliability, resulting in over 20,000 simulations for each portfolio. 

The portfolios were modeled such that options were implemented only when needed to 

address specific vulnerabilities, thus minimizing the investment simulated in the analysis. As 

shown in the table, inclusion of the portfolios was projected to improve the ability to meet 

Basin resources needs (i.e. reduce vulnerabilities). The vulnerabilities related to critical 

Upper Basin and Lower Basin water delivery metrics were reduced by 50 percent or more. 

The results for metrics related to electrical power, water quality, recreation, and ecological 

resources demonstrate reductions of a similar percentage in vulnerabilities. Only the metric 

related to flood control below Hoover Dam shows a slight increase in vulnerability due to the 

potential for higher reservoir storage (and higher likelihood of high release) when portfolios 

were included. 

Although these reductions in vulnerabilities are encouraging, vulnerabilities continue to be 

present under some conditions, even when every option was implemented as soon as it was 

assumed to be available. This result is primarily because of the hydrologic conditions driving 

those vulnerabilities. Statistical analysis was performed to determine the specific hydrologic 

conditions (e.g., droughts of a particular length) that tended to result in certain critical 

vulnerabilities (e.g., Lee Ferry deficit and Lake Mead elevation less than 1,000 feet msl). 

Under Baseline conditions, the potential for these critical vulnerabilities was found to be 

strongly correlated to long-term mean natural flows at Lees Ferry below the historical 

average of 15.0 maf and droughts of 8 years or greater in duration. 

Although the implementation of the portfolios does not completely eliminate the occurrence 

of such critical vulnerabilities, the portfolios are successful in significantly improving the 

resiliency of Basin resources to these vulnerable hydrologic conditions. With portfolios in 

place, the system is able achieve similar levels of reliability under more adverse hydrologic 

conditions. Specifically, with portfolios in place, the long-term average flow to which the 

Basin is vulnerable is about 0.5 mafy less and the magnitude of the 8-year period of lowest 

flows is reduced about 1 mafy. This type of information provides insight into specific 

hydrologic conditions that the system should be able to successfully endure and can inform 

water managers when crafting strategies to effectively hedge against those events.
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TABLE 4 

Summary of System Reliability Outcomes (Percent of Years Vulnerable) for Baseline and Portfolios for All Scenarios, 2041–2060 Period

Resource System Vulnerability Baseline Portfolio A Portfolio B Portfolio C Portfolio D

Water Delivery Upper Basin (Lee Ferry Deficit) 7% 2% 2% 3% 3% 

Lower Basin (Lake Mead pool elevation below 1,000 feet msl) 19% 3% 3% 5% 6% 

Electrical Power Upper Basin Generation (below 4,450 gigawatts per hour per year 

for 3 consecutive years)

18% 9% 10% 10% 11% 

Lower Basin Generation (Lake Mead pool elevation below 

1,050 feet msl)

42% 14% 14% 29% 20% 

Flood Control Critical River Stage below Hoover Dam (greater than 28,000 cubic 

feet per second)

1% 4% 4% 3% 34%

Water Quality Salinity below Parker Dam (greater than numeric criteria)1 0% 0% 0% 0% 0%

Recreation Colorado River Boating (days less than current conditions with 

variable hydrology) 

30% 14% 16% 17% 19% 

Lake Powell Shoreline Facilities (pool elevation less than 3,560 feet 

msl)

24% 11% 11% 12% 13% 

Lake Mead Shoreline Facilities (pool elevation less than 1,080 feet 

msl)

57% 31% 30% 37% 39%

Ecological Colorado River Flow (less than targeted flow conditions) 38% 40% 28% 28% 31%

Hoover Dam to Davis Dam Flow Reductions (annual flow change 

greater than 845 thousand acre-feet) 

12% 4% 4% 7% 8% 

1 Due to modeling limitations, values reported do not include results from the Downscaled GCM Projected scenario. 
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Although the portfolio analysis successfully demonstrated that system reliability can be 

improved, it is not without significant cost and performance tradeoffs. Figure 3 illustrates the 

performance across portfolios by water supply scenario in terms of addressing the critical Upper 

Basin and Lower Basin vulnerabilities.

Portfolio B favors options believed to have higher certainty of available water supply once 

implemented. As shown in figure 3 (on the right), this portfolio performs as well or better than 

all the other portfolios for addressing the Lower Basin vulnerability. The portfolio is less 

effective than Portfolios A and C for the Upper Basin vulnerability (figure 3, left), particularly in

the Downscaled GCM Projected supply scenario (bottom row).

Portfolio C, while focused on options that favor lower energy needs and less environmental 

impacts, is more dependent on shifting social values towards additional water conservation and 

reuse. Choosing to implement options characterized as having low energy needs (as a surrogate 

for potential environmental impacts) might come at the expense of having a less certain longterm water supply. However, this portfolio performs well for addressing the Upper Basin 

vulnerability (figure 3, left) and is particularly effective under the Downscaled GCM Projected 

supply scenario (figure 3, bottom row). The effectiveness of this portfolio for addressing Upper 

Basin reliability vulnerabilities is largely attributable to the inclusion of an Upper Basin water 

bank that specifically targets this vulnerability. Portfolio C is less effective, however, at 

addressing the Lower Basin reliability vulnerabilities (figure 3, right). 
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FIGURE 3

Percent of Years Vulnerable for Upper Basin (left) and Lower Basin (right) Vulnerabilities in 2041–2060 with Portfolios, by Water 

Supply Scenario

Tradeoffs also exist with respect to portfolio costs, and these differ depending on the specific 

future conditions. As shown in figure 4, the annual cost, in 2012 dollars, for implementing the 

portfolios ranges from approximately $2.5 billion to $3.5 billion in the year 2060 when 

considering the median of the Observed Resampled supply sequences, and from $3.6 billion to 

$5.8 billion when considering the median of the Downscaled GCM Projected supply sequences. 

The variability of the cost (reflected by the inter-quartile range or the length of the bars) reflects 

the varying size of the portfolios in different future conditions. Because of the appraisal-level 

option cost estimating used in the Study, the cost values contain additional uncertainty not 

directly reflected in these estimates. Across three supply scenarios (Observed Resampled, Paleo 

Resampled, and Paleo Conditioned), Portfolios B and D are generally shown to be less costly 

than Portfolios A and C. For the Downscaled GCM Projected water supply scenario tradeoffs 

between portfolios begin to become apparent. Specifically, Portfolio C leads to fewer vulnerable 

years with respect to Upper Basin vulnerability than Portfolios A and B, with an upper range of 

costs that is also lower than those for Portfolios A and B. Conversely, Portfolio A generally leads 

to the fewest vulnerable years with respect to Lower Basin reliability than other portfolios. 

The differences among the portfolios become more apparent in terms of costs and ability to 

reduce vulnerability as one focuses on the future conditions that are particularly stressing to the 
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Basin. For water supply conditions that are less favorable, such as in the “Lowest Streamflow” 

subset of sequences (figure 4, bottom row), two distinct tradeoffs between reduction in 

vulnerability and cost across the portfolios are apparent. For the Upper Basin vulnerability, 

Portfolio C both performs better than Portfolios B and D in terms of reducing this vulnerability

and has a lower range of costs than Portfolios A and B. For the Lower Basin vulnerability, 

however, Portfolio B reduces vulnerability more than Portfolios C and D and also results in 

lower costs than Portfolio A. 

FIGURE 4 

Portfolio Cost and Percent of Years Vulnerable for Upper Basin (left) and Lower Basin (right) Vulnerability for 

2041—2060 across Water Supply Scenarios and Lowest Streamflow Conditions

(1) Lowest Streamflow Conditions are defined as those in which the average of the 2012—2060 natural flow at Lees Ferry is less 

than 14 mafy and the lowest 8-year natural flow at Lees Ferry from 2012–2060 averages less than 11 mafy. 
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Although the portfolios explored in the Study address water supply and demand imbalances 

differently, there are commonalities across the options implemented for each portfolio. All of the 

portfolios incorporate significant agricultural water conservation, M&I water conservation 

(1 maf each of both additional M&I and agricultural conservation was implemented in all 

portfolios), energy water use efficiency, and some levels of weather modification. However, 

some options were implemented more frequently in response to challenging water supply 

conditions. For example, ocean and brackish water desalination, wastewater reuse, and 

importation options were implemented for the most challenging water supply conditions in 

portfolios in which they were included. Future planning will require careful consideration of the 

timing, location, and magnitude of anticipated future Basin resource needs. The purpose of 

exploring these portfolios is not to identify a “best” portfolio or strategy, but to acknowledge that 

there are various ways to address the water supply and demand imbalance and to recognize that 

each approach has implications to be considered in future planning processes and decisionmaking. 

5.0 Study Limitations

Although the technical approach of the Study was based on the best science and information 

available, as with all studies, there were limitations. The detail at which results are reported or 

the depth to which analyses were performed in the Study was limited by the availability of data, 

assessment methods, and the capability of existing models. These limitations provide 

opportunities for additional research and development and the improvement of available data, 

which will be pursued in efforts independent of the Study. Notable Study limitations include the 

following: 

• Ability to Assess Impacts to Basin Resources – The ability to assess impacts to Basin 

resources, particularly in the Upper Basin, was limited by the spatial and temporal detail of 

the Colorado River Simulation System (CRSS), the primary model used in the Study. In 

particular, the Study’s assessment of water deliveries at local level, and ecological and 

recreational impacts were affected by these limitations. Future efforts will evaluate ways to 

improve the assessment of these resources in future studies which will include enhancements 

to CRSS, as appropriate.

• Treatment of Lower Basin Tributaries – CRSS uses historical inflows (not natural flows) 

based on USGS streamflow records for four tributaries below Lees Ferry (the Paria, Little 

Colorado, Virgin, and Bill Williams rivers). In addition, the Gila River is not included in 

CRSS. The current treatment of these tributaries limited the ability of the Study to fully 

assess the natural supply of the Basin, and the data and methodological inconsistencies 

present in the Reclamation’s Consumptive Uses & Losses Reports limited the ability of the 

Study to gain a more complete understanding of historical consumptive use in the Basin. The 

Basin States will also work with Reclamation in fulfilling the commitments regarding the 

Lower Basin tributaries specifically described in Technical Report C – Water Demand 

Assessment, Appendix C11. 

• Treatment of Agricultural Land Use in Water Demand Scenarios – The development of 

the water demand storylines included participation from a broad range of stakeholders. The 

storylines were developed to represent a range of plausible futures regarding future demand. 

However, the assumptions in some storylines with regard to key driving forces resulted in the 
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same directional changes in demand across the storylines. For example, the assumptions of 

continued conversion of agricultural land use to urban land use and lower-economic value 

crops being phased out in some areas led to overall agricultural land use (i.e., the number of 

irrigated acres) decreasing over time over all scenarios. Although some scenarios do show 

increasing agricultural land use at a state and local level, given recent projections of 

increased agricultural productivity necessary to meet future food needs, plausible futures 

should include increases in land use. 

• Option Characterization Process – The option characterization process strived for 

objectivity and consistency. The limitations identified during the characterization process 

included geographic limitations due to the extensive size of the basin and regional variety,

the appraisal-level of the analysis, potential subjectivity during the characterization process, 

and significant uncertainty due to limited data. Specifically for those options associated with 

agricultural and M&I conservation and reuse, a detailed assessment by individual location for 

those options was not performed. Instead, these options were characterized at a Basin-wide 

level. The resulting assumptions were adopted for purposes of the Study and do not 

necessarily reflect achievable, or even desirable, local conservation goals for individual 

municipalities or agricultural locations. Further, not all stakeholders in the Study were in 

agreement with all characterization results, but it was recognized that future efforts beyond 

the Study should result in more in-depth assessments of the options and reduced uncertainty. 

• Consideration of Options – Due to the legal, regulatory, and sometime technical complexity 

of the options submitted, not all categories of options submitted underwent a quantitative

assessment. As such, portfolios were largely limited to groups of options that lend

themselves to modeling implementation within the Study’s timeframe, i.e. those that increase 

supply or reduce demand, with the exception of the Upper Basin water bank concept. The 

options modeled in CRSS do not necessarily reflect the entire range of innovative options 

and strategies that should continue to be explored in future efforts. 

6.0 Future Considerations and Next Steps 

Colorado River water managers and stakeholders have long understood that growing demands on 

the Colorado River system, coupled with the potential for reduced supplies due to climate change 

may put water users and resources relying on the river at risk of prolonged water shortages in the 

future. The magnitude and timing of these risks differ spatially across the Basin. In particular, 

areas where demand is at or exceeds available supply are at a greater risk than others. The Study 

builds on earlier work and is the next significant step in developing a comprehensive knowledge 

base and suite of tools and options that will be used to address the risks posed by imbalances 

between Colorado River water supply and resource needs in the Basin. 

The Study confirms that the Colorado River Basin faces a range of potential future imbalances 

between supply and demand. Addressing such imbalances will require diligent planning and 

cannot be resolved through any single approach or option. Instead, an approach that applies a 

wide variety of ideas at local, state, regional, and Basin-wide levels is needed. The Study’s 

portfolio exploration demonstrated implementation of a broad range of options can reduce Basin 

resource vulnerability and improve the system’s resiliency to dry hydrologic conditions while 

meeting increasing demands in the Basin and adjacent areas receiving Colorado River water. 
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The Study indicates that targeted investments in water conservation, reuse, and augmentation 

projects can improve the reliability and sustainability of the Colorado River system to meet 

current and future water needs. Ultimately, the Study is a call to action. To implement the water 

conservation, reuse, and augmentation projects identified in the Study, significant additional 

efforts are required immediately. These additional efforts, or next steps, include a commitment 

to further analysis and planning in many areas related to the Study. 

In summary, there are several future actions that must take place to move implement solutions to 

resolve imbalances in the Basin. First, significant uncertainties related to water conservation, 

reuse, water banking, and weather modification concepts must be resolved in order to adequately 

implement these approaches. Second, costs, permitting issues, and energy needs relating to 

large-capacity augmentation projects need to be identified and investigated through feasibilitylevel studies. Third, opportunities to advance and improve the resolution of future climate 

projections should be pursued and enhancements to the operational and planning tools used in 

the Colorado River system to better understand the vulnerabilities of the water-dependent uses, 

including environmental flows, should be explored. Fourth, as projects, policies, and programs 

are developed, consideration should be given to those that provide a wide-range of benefits to 

water users and healthy rivers for all users. 

In recognition of their ongoing joint commitment to future action, Reclamation will convene the 

Basin States along with tribes, other Colorado River water entitlement holders, conservation 

organizations, and other interested stakeholders in early 2013 to conduct a workshop to review 

the recommended next steps and initiate actions to implement next steps to resolve the current 

and potentially significant future imbalances in the Colorado River system. In early 2013 

Reclamation will also consult and work with tribes regarding tribal water issues reflected in this 

report.
EXECUTIVE SUMMARY ES-22 DECEMBER 2012

Disclaimer

The Colorado River Basin Water Supply and Demand Study (Study) is funded jointly by the Bureau of 

Reclamation (Reclamation) and the seven Colorado River Basin States (Basin States). The purpose of 

the Study is to analyze water supply and demand imbalances throughout the Colorado River Basin and 

those adjacent areas of the Basin States that receive Colorado River water through 2060; and develop, 

assess, and evaluate options and strategies to address the current and projected imbalances. 

Reclamation and the Basin States intend that the Study will promote and facilitate cooperation and 

communication throughout the Basin regarding the reliability of the system to continue to meet Basin

needs and the strategies that may be considered to ensure that reliability. Reclamation and the Basin 

States recognize the Study will have to be constrained by funding, timing, and technological and other 

limitations, which may present specific policy questions and issues, particularly related to modeling 

and interpretation of the provisions of the Law of the River during the course of the Study. In such 

cases, Reclamation and the Basin States will develop and incorporate assumptions to further complete 

the Study. Where possible, a range of assumptions will typically be used to identify the sensitivity of 

the results to those assumptions.

Nothing in the Study, however, is intended for use against any Basin State, any federally recognized 

tribe, the Federal government or the Upper Colorado River Commission in administrative, judicial or 

other proceedings to evidence legal interpretations of the law of the river. As such, assumptions 

contained in the Study or any reports generated during the Study do not, and shall not, represent a legal 

position or interpretation by the Basin States, any federally recognized tribe, Federal government or 

Upper Colorado River Commission as it relates to the law of the river. Furthermore, nothing in the 

Study is intended to, nor shall the Study be construed so as to, interpret, diminish or modify the rights 

of any Basin State, any federally recognized tribe, the Federal government, or the Upper Colorado 

River Commission under federal or state law or administrative rule, regulation or guideline, including 

without limitation the Colorado River Compact, (45 Stat. 1057), the Upper Colorado River Basin 

Compact (63 Stat. 31), the Utilization of Waters of the Colorado and Tijuana Rivers and of the 

Rio Grande, Treaty Between the United States of America and Mexico (Treaty Series 994, 59 

Stat. 1219), the United States/Mexico agreement in Minute No. 242 of August 30, 1973, (Treaty 

Series 7708; 24 UST 1968) or Minute No. 314 of November 26, 2008, or Minute No. 318 of 

December 17, 2010, or Minute No. 319 of November 20, 2012, the Consolidated Decree entered by the 

Supreme Court of the United States in Arizona v. California (547 U.S 150 (2006)), the Boulder Canyon 

Project Act (45 Stat. 1057), the Boulder Canyon Project Adjustment Act (54 Stat. 774; 43 U.S.C. 

618a), the Colorado River Storage Project Act of 1956 (70 Stat. 105; 43 U.S.C. 620), the Colorado 

River Basin Project Act of 1968 (82 Stat. 885; 43 U.S.C. 1501), the Colorado River Basin Salinity 

Control Act (88 Stat. 266; 43 U.S.C. 1951) as amended, the Hoover Power Plant Act of 1984 (98 Stat. 

1333), the Colorado River Floodway Protection Act (100 Stat. 1129; 43 U.S.C. 1600), the Grand 

Canyon Protection Act of 1992 (Title XVIII of Public Law 102-575, 106 Stat. 4669), or the Hoover 

Power Allocation Act of 2011 (Public Law 112-72). In addition, nothing in the Study is intended to, 

nor shall the Study be construed so as to, interpret, diminish or modify the rights of any federally 

recognized tribe, pursuant to Federal Court Decrees, State Court Decrees, treaties, agreements, 

executive orders and federal trust responsibility. Reclamation and the Basin States continue to 

recognize the entitlement and right of each State and any federally recognized tribe under existing law, 

to use and develop the water of the Colorado River system.