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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability 2 Historical and Contemporary Aspects of Colorado River Development Draining an area of over 240,000 square miles, the Colorado River and its main tributary streams originate high within the mountains of western Wyoming, central Colorado, and northeastern Utah. With snowpack accumulating as high as 14,000 feet above sea level, the mainstem of the upper Colorado River receives large amounts of snowmelt from several major tributaries: the Green River flowing south out of Wyoming; the Duchesne River in northern Utah; the Dolores, Gunnison, White, and Yampa rivers in Colorado; and the San Juan River flowing northwest through New Mexico. When it reaches the Canyonlands region of southern Utah (site of Lake Powell), the Colorado’s streambed lies hundreds of feet below the surrounding mesas and plateaus. After crossing the Utah-Arizona border and passing Lees Ferry, the river flows westward through Grand Canyon National Park. A further 160 miles downstream—after receiving flows from the Virgin River that drains southwestern Utah and parts of southern Nevada—the Colorado reaches Boulder and Black canyons (which rim much of Lake Mead) and forms the Arizona-Nevada border. Turning southward, the center of the streambed forms the 200-mile-long border between California and Arizona. Near the southern edge of this border, the Gila River (which, along with its tributary the Salt River, drains most of central and southern Arizona) enters the lower Colorado from the east. Just below its confluence with the Gila, the Colorado River enters the state of Sonora, Mexico. There, most of the Colorado’s remaining flow is consumed by irrigated agriculture, leaving little water to reach the Gulf of California through the Colorado’s historically expansive delta (USBR, 1947; Waters, 1946).
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability With an annual mean discharge of about 15 million acre-feet, the Colorado River is not a giant among the world’s rivers. The Colorado River traverses one of North America’s driest regions, however, thus offering opportunities for economic development and growth unmatched by any other water source in this arid region. For the past 100 years these possibilities have spurred myriad political contests among irrigators, businesses, civic boosters, politicians, tribes, ranchers, government officials, engineers, and, more recently, environmental groups and recreational users, all seeking a voice in Colorado River allocation decisions. A root cause of these conflicts is the hydrologic reality that, although roughly 90 percent of the river’s flow originates in the upper basin states of Colorado, New Mexico, Utah, and Wyoming, much of the demand for the river’s water emanates from the lower basin states of Arizona, California, and Nevada (Hundley, 1966, 1975; Martin, 1989; Moeller, 1971; Pearson, 2002; USBR, 1947). The story of the development, management, and use of the Colorado River was initially one where concerns over unreliable water supplies were resolved by technological advances, accompanied by legal and administrative arrangements. More recently, this story reflects the concerns of the federal government, the basin states, tribes, municipalities, and other major water users adapting to conditions not fully anticipated when the legal regime and the major dams were put in place. In the early 20th century, the sparsely populated and largely rural upper basin states watched Southern California’s rapid agricultural and urban growth with trepidation. Trepidation turned to fear in 1922 when the Supreme Court held that the western doctrine of prior appropriation could govern apportionment of interstate streams in the arid West. Soon thereafter, the upper basin states succeeded in negotiating the first interstate compact to allocate flows in an interstate stream. The 1922 Colorado River Compact divided the river between the upper and lower basins and reserved unused water for future development in the four upper basin states. Beginning in 1922, California led the fight for the construction of a multipurpose dam on the lower Colorado (decades later they found that the price for having Hoover Dam constructed was a federal apportionment of the river among the three lower basin states). During World War II, political considerations led to a treaty that guaranteed Mexico a supply and in 1948 the upper basin states agreed to an allocation formula among
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability themselves. Once a legal regime (often referred to as “The Law of the River”) was in place governing Colorado River water allocations, Congress supported construction of dams on the mainstem and tributaries to support the states’ compact rights and delivery obligations. This regime has permitted the basin and major, nearby urban centers—such as Albuquerque, Denver, Los Angeles, Salt Lake City, and San Diego—to grow, but in recent decades it has become stressed by several factors. These include the accommodation of Indian claims, rapid population growth (especially in Arizona and in southern Nevada), the need to control downstream salinity caused by irrigation runoff, disturbances to the Grand Canyon ecosystem caused by the operation of Glen Canyon Dam, and interests in restoring a remnant of the Colorado River Delta in Mexico. These stresses are occurring in the face of the long-standing recognition that the flow estimates on which allocations were negotiated in the 1920 were based upon data drawn from a relatively short and very wet period, and thus turned out to be overly optimistic. Moreover, changes in regional climate conditions may further reduce net available water supplies. Variations in climate and river flows have been an integral part of this history of Colorado River development. The gathering and analysis of hydroclimatic data assume economic significance because, across the basin, hydrology and climate are linked to larger legal constructs and water development projects. Moreover, the implications of climate and hydrologic studies are related to demographic, water use, and other social and management trends. In reviewing key Colorado River legal agreements and treaties, the history of dam and water storage projects, and demographic and other trends affecting the basin, this chapter does not seek to present an exhaustive discourse; rather, it provides a demographic and legal context for appreciating the significance of subsequent discussions involving climate studies, hydrologic records, water use technologies and practices, and adjustments to drought. This chapter explores this history of the past 150 years or so of Colorado River water development in greater detail. It divides this period into four broad phases: (1) the 1860s through 1920, (2) 1920 to 1965, (3) 1965 to the mid-1980s, and (4) the mid-1980s to the present.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability EARLY EXPLORATION AND INITIAL FORAYS IN COLORADO RIVER DEVELOPMENT: 1860s TO 1920 This report focuses on Colorado River development from roughly the middle of the 19th century until the present. Prior to this period there was a rich and extensive history of exploration, irrigated agriculture, and related means for coping with drought and aridity. Spanish explorers led by Coronado in 1540, as well as other expeditions and individuals, referred to the river as the “Colorado” in reference to the reddish silt that—before construction of storage dams—was suspended in the stream’s lower reaches. Irrigation in the southwestern United States dates back several centuries to the Hohokam of southern Arizona, who cultivated fields in what is now the greater Phoenix metropolitan region. Spanish settlers, especially in present-day northern New Mexico, later established acequia (ditch) systems for irrigation in the 1700s; many of these are still in use. For purposes of this report, discussions of contemporary water management and scientific issues related to the Colorado River basin date back to the 19th-century origins of Anglo-American irrigated agriculture, and to the growth of urban water demand initiated by Los Angeles in the early 20th century. Well before this period, there was an extensive prehistory of water use in the basin, which is chronicled in a substantial body of archaeological and ethnohistorical research (see Brooks, 1974; Dart, 1989; Fish and Fish, 1994; Meyer, 1984). Although a review of long-term social processes dating back several centuries is beyond this report’s scope, this body of knowledge could be a valuable resource in helping water managers better cope with hydroclimatic variability. It could be used, for example, in scenario construction, water conservation practices (e.g., reviewing past water harvesting techniques), and forecasting by analogy (see Glantz, 1988). From the mid-19th century through 1920, the Colorado River basin saw both Anglo-American exploration and the inception of large-scale irrigated agriculture. In the 1860s the upper Colorado River basin constituted one of the last great unexplored regions of North America. Explorer and scientist John Wesley Powell led two important expeditions through this region, the first in 1869 down the Colorado River through Grand Canyon, and the second 2 years later. Boosted by a popular self-penned account of Powell’s expeditions, by
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability the late 19th century the Colorado watershed—or at least that encompassing the Grand Canyon and Utah’s Canyonlands—had attained almost mythic status in the minds of many Americans (Powell, 1895; Stegner, 1954; Worster, 2000). The period from the mid-1860s to 1920 witnessed the diffusion of many new irrigation systems throughout the Colorado River basin. In the 1860s Mormon farmers were cultivating fields with water from the Virgin River and, in central Arizona, major irrigation diversions from the Salt and Gila rivers were under way by the end of the decade. In the 1870s farmers began diverting lower Colorado River water for irrigation near Blythe, California, and in the 1880s farmers near Grand Junction, Colorado, were using upper Colorado River flows to nourish crops. These early diversions were relatively minor compared with later development but they established an important precedent that demonstrated future economic and agricultural possibilities (Hundley, 1975; Kleinsorge, 1941; Raley, 2001; Zarbin, 1984, 1997). Plans for the first major diversion of the Colorado River began in the late 1890s. During this period the California Development Company launched an ambitious plan to divert Colorado River water from near the Mexico-U.S. border and convey it more than 50 miles west to a remote part of Southern California known to 19th-century geographers as the “Colorado Desert.” Company boosters changed the region’s name to the more inviting “Imperial Valley” and set out to create an agricultural empire encompassing several hundred thousand acres. Imperial Valley irrigation offered enormous possibilities because (1) much of the valley was below sea level, (2) as much as 3 million acre-feet of water could be taken annually from the Colorado River to support irrigation, and (3) in ancient times a channel of the Colorado River—the “Alamo River”—had carried water into the valley. This latter factor proved particularly important because the Alamo Canal of the California Development Company largely followed the ancient channel formed by the Alamo River—thus necessitating little new (and expensive) excavation. A downside to the project (at least in the eyes of many investors and farmers) was that the company’s Alamo canal extended through Mexican territory for 50 miles before crossing the international border back into the United States (De Stanley, 1966; Hundley, 1992; Starr, 1990).
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability By 1900 the California Development Company was delivering water to the Imperial Valley and thousands of settlers were flocking to the region. In 1904 the upper end of the Alamo Canal was reconfigured to counter problems with silt accumulation; unfortunately for the company, in 1905 this canal’s newly built wooden headgate was overwhelmed by heavy floods. For the next 2 years the entire flow of the Colorado River descended into the Imperial Valley, drowning crop land and creating a large new waterbody—the Salton Sea—which still exists today. In 1907 the canal heading was finally closed off through laborious efforts of the Southern Pacific Railroad and the flooding stopped, but not before the California Development Company lay in financial ruin. After the company’s remaining assets passed to the newly formed Imperial Irrigation District in 1911, local farmers began soliciting federal government support for (1) a flood control dam across the Colorado River to prevent a recurrence of the 1905-1907 disaster, and (2) construction of an “all-American” canal that could deliver Colorado River water to the Imperial Valley without passing through Mexico. Intense lobbying for what eventually became the Boulder Canyon Project Act was under way by 1920 (De Stanley, 1966; Hundley, 1975; 1992; Starr, 1990). LARGE-SCALE COLORADO RIVER WATER DEVELOPMENT: 1920 TO 1965 Planning for Boulder (later Hoover) Dam in the early 1920s marked the beginning of the second period of Colorado River development; the completion of Glen Canyon Dam in 1964 signaled its end. These two dams comprise the centerpiece of the U.S. federal Colorado River water storage infrastructure. The years 1920-1965 saw a dramatic rise in the influence and prestige of the U.S. Bureau of Reclamation, and most of the basin’s large dams were either planned or constructed during this period. Termed the “Go-Go Years” by writer Mark Reisner, the post-World War II era was the most active period of large dam construction in U.S. history. Glen Canyon Dam represents one of the last large western water storage projects, and no comparable water project has been built since in the Colorado River basin. It was also completed at a time when many U.S. citizens were beginning to express concerns about the environmental impacts of
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability large storage dams (Billington and Jackson, 2006; Reisner, 1986; Worster, 1985). Complementing the growth of the basin’s water storage infrastructure, the 1920-1965 period also witnessed the creation of a complex legal structure governing allocations of river flow. Collectively, this legal framework is known as the Law of the River and it consists of interstate compacts, international agreements, water delivery contracts, and myriad other legal obligations. Milestones within this body of agreements, legislation, and court rulings (many of which were forged in the 1920-1965 period) are the 1922 Colorado River Compact, the 1928 Boulder Canyon Project Act, 1944 and 1973 international agreements with Mexico, the 1948 Upper Colorado River Basin Compact, the 1956 Colorado River Storage Project (CRSP) Act, the landmark Supreme Court decision (1963) and decree (1964) in Arizona v. California, the 1968 Colorado River Basin Project Act, the 1992 Grand Canyon Protection Act. Colorado River Water Storage and Delivery Infrastructure Hoover Dam and Lake Mead Through the late 19th and early 20th centuries, the Colorado River’s hydroelectric power potential attracted little attention because of a paucity of local demand. Similarly, the Colorado River was remote from any urban settlement that might seek to tap its flows (Figure 2-1). But by the 1920s economic conditions in the southwestern United States—especially in the greater Los Angeles region of Southern California—were changing rapidly, and earlier doubts about the economic viability of exploiting the river for municipal growth had largely disappeared. In this light, the driving force behind Boulder Dam can be traced to Southern California political and economic interests that were tied to both the Imperial Valley and to rapidly urbanizing Los Angeles. In addition, the U.S. Reclamation Service (renamed the Bureau of Reclamation in 1923) had long advocated the need for a dam on the lower Colorado in the name of comprehensive river development. After the 1905 flood that damaged existing water control infrastructure along the river in California, the
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability FIGURE 2-1 Colorado River upstream of the site of Boulder/Hoover Dam, ca. 1925. This stretch of the river today lies inundated by Lake Mead (impounded by Hoover Dam). SOURCE: Postcard ca. 1925, no publisher. need for greater river control became more pressing. The Bureau of Reclamation eventually merged its vision with the more immediate interests of Imperial Valley farmers and the City of Los Angeles for a significant flood control and water storage project on the river (Billington and Jackson, 2006; Hundley, 1992; Kleinsorge, 1941; Moeller, 1971). Owing to a combination of geologic and climatic factors, the desert lands of southeastern California discharge only a minuscule amount of water into the Colorado River. Nevertheless, irrigators and civic boosters in Southern California were well positioned to lay claim to—and withdraw—huge quantities of water from the Colorado before any other states in the watershed could develop projects of comparable scale (Figure 2-2). By the early 1920s California legislators (with support from the Reclamation Service) were actively promoting federal construction of Boulder Dam. This, in turn, raised concerns among other Colorado basin states that feared completion of the dam would allow California to divert a large portion, perhaps most, of the river’s flow. In addition, the huge storage project could
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability FIGURE 2-2 Map of proposed Boulder Dam Project and Colorado River Aqueduct, ca. 1930. SOURCE: Metropolitan Water District of Southern California. only be justified economically if financing was guaranteed by the sale of hydroelectric power, something that the privately financed electric power industry opposed. Taking all these factors into account, Senate approval of the Boulder Canyon Project Act required significant (although not necessarily unanimous) support from the same western states that feared California’s monopolization of the Colorado River. The result of various sets of state and federal negotiations was the Colorado River Compact (described more fully below), a politically driven agreement between the upper basin and lower basin states dividing rights to Colorado River flows (Billington and Jackson, 2006; Brigham, 1998; Hundley, 1975, 1992; Kleinsorge, 1941; Moeller, 1971).
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability Following passage of the Boulder Canyon Project Act in 1928, construction of the 726-foot-high Boulder/Hoover Dam was started in 1931 under authority of the Bureau of Reclamation. Completed in 1935, Hoover Dam today impounds Lake Mead, a reservoir with a storage capacity of more than 28 million acre-feet1 (Figure 2-3). By 1937 hydroelectric power from the dam was being transmitted to Southern California, and by 1940 power was used to pump water through the Metropolitan Water District of Southern California’s Colorado River Aqueduct, a major water conduit serving domestic and industrial water supply needs in Los Angeles and surrounding cities (Bissell, 1939; Kleinsorge, 1941; Stevens, 1988). FIGURE 2-3 Hoover Dam, ca. 1940. SOURCE: U.S. Bureau of Reclamation. 1 Twenty-eight million acre-feet is roughly enough water to supply the service area of the Metropolitan Water District of Southern California—which serves the coastal plain of Southern California from Ventura southward to San Diego—for 7 years.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability Glen Canyon Dam and Lake Powell Glen Canyon Dam was authorized as part of the 1956 CRSP Act, which authorized other water projects for the upper Colorado River basin (see following section). Following passage of the CRSP in April 1956, engineers and surveyors were at the dam site in July, and in October 1956 the first ceremonial blast was set off on the canyon wall (Rusho, unpublished manuscript). Construction of the dam was staged from the construction town of Page, Arizona, and, although a labor strike shut down construction of the dam for a short period in 1959, the dam and its power plant were completed on schedule (Figure 2-4 shows Glen Canyon Dam under construction). Construction of Glen Canyon Dam neared completion in 1963, at which time its diversion tunnels were closed and Lake Powell began to rise (and eventually was filled in 1980). Officially dedicated in 1966, Glen Canyon Dam stands over 700 feet high and impounds Lake Powell, which has a storage capacity of 27 million acre-feet. The dam is located 15 miles downstream from the Arizona-Utah border and 11 miles upstream from Lees Ferry. With a reservoir comparable in size to Lake Mead, storage provided by Lake Powell helps ensure that the upper basin states meet their water delivery obligations to the lower basin. Glen Canyon Dam feeds water into a large hydroelectric power plant, and power revenues were used to help finance construction costs (see Martin  for more details on the construction of Glen Canyon Dam). Colorado River Legal Framework: The Law of the River The term “Law of the River” refers not to a single law, but rather to a complex array of agreements, legislation, court decisions and decrees, contracts, and regulatory schedules relating to the Colorado River, including a treaty with Mexico, two major multistate agreements (or compacts), Supreme Court rulings, and myriad other federal and state laws, acts, and regulations. In many ways, the foundation of the Law of the River was defined in the 1920s by the Colorado River Compact and the Boulder Canyon Project Act; over the ensuing decades, it expanded and evolved in numerous ways to incorporate new demands and shifting social and economic trends.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability FIGURE 2-7 Western U.S. drought conditions, 2000-2006. SOURCE: http://www.drought.unl.edu/dm/archive.html. The U.S. Drought Monitor is a partnership between the National Drought Mitigation Center (NDMC), U. S. Department of Agriculture, and National Oceanic and Atmospheric Administration. Map courtesy of NDMC UNL.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability BOX 2-3 Defining Drought Clear definitions of drought are elusive. Drought is generally understood in terms of the definition offered in Webster's Dictionary: dryness; want of rain; or a prolonged period of dryness. Drought is a normal part of climate in nearly all of the United States but it is of special concern in arid regions of the western United States, where precipitation is often in short supply and where one thus might say drought exists much of the time. Drought can be defined in different terms, including meteorological, agricultural, hydrologic, and socioeconomic (Wilhite and Glantz, 1985). Hydrologic definitions of drought are of particular interest within this report, as Colorado River water managers generally define drought in terms of reservoir inflows. The Colorado River basin drought of the early 21st century saw well below normal inflows into Lake Powell for the 5-year period 2000-2004. It should be noted, however, that 1999 and 2005 both had only slightly above-normal inflows, and one or two years of slightly above normal inflows do not end a drought of such magnitude. For 1999-2005, average inflows into Lake Powell were below normal. The 2006 water year is likely to extend this trend. A basic concept invoked in understanding drought is that of a water budget. Water is held in storage buffers such as soil root zones, aquifers, lakes, reservoirs, and surface stream flows. These buffers act as water supplies, are subject to demands, and are replenished and lose water at varying rates. When losses exceed replenishment, impacts are experienced and, at lower storage levels, become increasingly severe. In essence, drought is defined by its impacts on both natural and manmade environments because without impacts there is no drought, no matter how dry it might be. Drought infers a relationship between supply rates and demand rates; drought is not simply a supply-side phenomenon, but also depends on water demands. Without demands, there is no drought, whether a given supply of water is big, small, or even zero. It can be difficult to determine exactly when a drought has begun or ended, and there can be differences of opinion over whether a drought actually exists. Droughts begin slowly. They may be interrupted by wet periods, during which it is not clear if precipitation will continue or if dry conditions will return. A drought may not be widely recognized until it has been under way for several months or longer, and it can be particularly difficult to recognize in arid regions that experience seasonal dry periods. Recognizing that drought began in some parts of the Colorado River basin in the late 1990s, and that it is ongoing in many areas and may not abate any time soon, this report uses the descriptors of drought of the early 21st century and drought of the early 2000s to refer to the drought that has affected Colorado River hydrology in this period.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability TABLE 2-3 Unregulated Inflow to Lake Powell Water Year a Percent of Average 1999 109% 2000 62% 2001 59% 2002 25% 2003 52% 2004 51% 2005 109% a “Water year” refers to the period from October 1 to September 30 of the following year (e.g., Water Year 2004 refers to the period from October 1, 2003, until September 30, 2004). SOURCE: Fulp (2005b). (Fulp, 2005a). In early 2005 Lake Powell was at its lowest level of storage since 1969, when it was initially filling (Figures 2-8 and 2-9), and Lake Mead had not been as low since 1967 (Fulp, 2005a). The drought of the early 2000s was severe by any measure; in terms of climate statistics, the probability is very low—less than 0.1—that any 5-year drought period since 1850 had been as dry as 2000-2004 (Woodhouse et al., 2006). During the early 21st century drought, the Colorado River storage system performed much like it had been designed to do and, even after 5 consecutive below-average years of precipitation and inflows, still held roughly 2 years of annual Colorado River flows (Fulp, 2005a). Precipitation across the Colorado River basin was closer to average conditions in 2005, but in 2006 drier conditions returned and were exacerbated by above-normal temperatures; July 2006, for example, was the second-warmest-ever month of July in the continental United States (http://www.noaanews.noaa.gov/stories2006/s2677.htm), and the 2006 average annual temperature for the contiguous United States was the warmest on record (and nearly identical to the record set in 1998; http://www.ncdc.noaa.gov/oa/climate/research/2006/ann/us-summary.html). It is not clear how drought will impact future reservoir storage levels, nor is it clear exactly how long it would require the storage system to refill once again. According to one estimate, it may require roughly 15 years of average hydrology to refill Lakes Powell and Mead (Jeanine Jones, California Department of Water Resources, personal communication, 2005). Closer-to-normal precipitation may
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability FIGURE 2-8 Storage in Lake Powell through December 1, 2006. Lake Powell’s capacity is 27 million acre-feet, including dead storage. Values shown do not include the volume of water in dead storage. SOURCE: Generated at http://www.usbr.gov/uc/crsp/GetSiteInfo. FIGURE 2-9 Glen Canyon Dam and Lake Powell, August 2004. Note the residual ring around the top of the lake caused by declining water levels. SOURCE: Courtesy of Brad Udall, University of Colorado.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability end the drought, but a return of drier conditions could extend it. Regardless of future precipitation conditions, higher levels of population and water demand will make it more difficult to fill reservoirs and meet future water demands and obligations. Coping with Drought and Increasing Water Demands The early 21st century drought has been notable for its hydrologic and related impacts, such as forest fires in some areas of the Colorado River basin. The drought, along with increasing population growth and water demands, stimulated a variety of responses. It is not possible to list here every new water use and drought mitigation strategy across the West, but this section introduces some notable drought responses in the early 2000s (Chapter 5 includes more detail on drought mitigation programs and studies). In response to drought conditions and increasing competition over the West’s water resources, the Department of the Interior initiated a program to help increase awareness of possible future conflicts over water, especially during drought. Entitled Water 2025: Preventing Crises and Conflict in the West, the program was started in 2003 in an effort to concentrate “existing federal financial and technical resources in key western watersheds and in critical research and development, such as water conservation and desalinization, that will help to predict, prevent, and alleviate water supply conflicts” (DOI, 2003). The Water 2025 program has provided limited funds for competitive “challenge grants,” much of which have gone to agricultural conservation projects. It has also sponsored workshops across the western United States that convened scientists, engineers, and water managers to discuss water shortage problems and possible solutions. A key premise driving the Water 2025 initiative is that “In some areas of the West, existing water supplies are, or will be, inadequate to meet the demands for water for people, cities, farms and the environment even under normal water supply conditions” (http://www.doi.gov/water2025/Water2025-Exec.htm). Water 2025 produced a map (see Figure 2-10) of areas across the western United States that may experience water supply crises by the year 2025. This figure shows that several areas of “highly likely” to experience conflicts lie within or adjacent to the Colorado River basin.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability FIGURE 2-10 Potential water supply crisis areas in the western United States. SOURCE: http://www.doi.gov/water2025/supply.html.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability Colorado River basin states are engaged in a variety of long-range water planning, drought management, and conservation plans and programs. The State of Colorado, for example, in 2004 began a Statewide Water Supply Initiative that examined all aspects of the state’s water uses through 2030 and discussed water supply options and management alternatives. The report’s first finding was that “[s]ignificant increases in Colorado’s population—together with agricultural water needs and an increased focus on recreational and environmental uses—will intensify competition for water” (CWCB, 2004). Another example of state-level planning for future water demands and shortages is the Arizona Drought Preparedness Plan. Issued in 2004 by the Governor’s Drought Task Force, this report provides guidance to water users within Arizona and serves as a foundation for a long-term, statewide water conservation strategy. In 2006, the California Department of Water Resources issued an extensive report on incorporating climate change into California state water management (California DWR, 2006). The other basin states are also involved in plans and studies aimed at enhancing water conservation, drought planning, and long-term water supply availability (Chapter 5 includes further discussion of drought management programs and initiatives in the region). An important development that grew out of drought conditions in the early 2000s was a letter of agreement signed by representatives of all seven Colorado River basin states (see Appendix A). Dated February 3, 2006, this letter was sent to the Secretary of the Interior in response to the Secretary’s request for the states to develop shortage guidelines and management strategies under low-reservoir conditions. No basin-wide shortage criteria existed prior to the 2000s, and the Secretary had declared that the Department of the Interior would develop these guidelines if the basin states were unable to arrive at a consensus agreement. The letter and the level of cooperation it represents constitute an important step toward devising the first formal set of shortage criteria among the seven basin states and, as such, provide some optimism regarding future interstate cooperation on Colorado River water supply issues.
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability COMMENTARY The past 150 years have been marked by four broad phases of Colorado River water development. The first era extended from the middle of the 19th century until roughly 1920. This period was characterized by explorations led by John Wesley Powell and by the origins of contemporary practices of irrigated agriculture. The second era extended from roughly 1920 to 1965. This period saw the signing of several crucially important water development agreements and rulings, and the construction of many major, multipurpose water projects. This era began with the planning for Boulder (Hoover) Dam and ended with the construction of Glen Canyon Dam. A third phase of Colorado River water development extended from 1965 until the mid-1980s. This period was characterized by ample water supplies that supported population growth and economic growth across a variety of sectors, including both urban and agricultural uses. Fewer dams and water projects were constructed during this period as compared to the 1920-1965 era. Water storage facilities constructed between 1920 and 1965 generally provided adequate water to support additional people and economic development. This provided a water supply “cushion” during periodic droughts, such as during drought across much of the basin in the late 1970s. The period also witnessed rising concerns regarding environmental impacts of large-scale dams and associated water supply systems. The fourth phase of regional water development began in the mid-1980s and continues today. This phase is characterized by limited water supply development and rapid population growth and urbanization. During the 1990s the four fastest-growing states (in percentage terms) in the nation were Nevada, Arizona, Colorado, and Utah, respectively. The basin's major cities, such as Las Vegas, Phoenix, and Tucson all experienced large increases in population, as did several cities on the basin’s periphery that depend on Colorado River water, such as Albuquerque, Denver, Los Angeles, and San Diego. Not only do these larger numbers of people increase urban water demands, many of these urban dwellers enjoy and support other, nontraditional uses of western water, namely instream flows for both recreation and environmental preservation. In some instances, population increases have been partly offset through water pricing and conservation measures that have reduced per capita demands, and by transfers of water from agricultural users. Increasing water de-
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability mands are also encouraging a reordering of priorities to favor uses with a stronger economic base and users possessing a greater willingness to pay for water. But as population and water demand continue to grow, urban water supply gains realized by conservation, water transfers, and other measures are eventually absorbed. The impact of high, steady population growth has been to increase water demands; in the face of limited water supplies, these increasing and broadening demands portend a decreasing ability to cope with drought conditions and heightened conflicts over limited water supplies. When the Colorado River Compact was signed in 1922, except for municipal water demands in Southern California, use of water for irrigated agriculture was a predominant concern. The basin was lightly populated and the river’s water was allocated equally between the upper and lower basins. At that time, population in the lower basin states was roughly double that in the upper basin states. Since that 1922 allocation the upper and lower basins experienced different levels of population growth and urbanization. The most important demographic feature in the ensuing years was population growth in Southern California (and to a lesser extent in Arizona). Today, population in the lower basin states is four to five times the population in the upper basin states. Fueled by this growing population, the lower basin states eventually began to use their full 7.5 million acre-feet annual allocation of Colorado River water. By contrast, the upper basin states have never used their full allocation of 7.5 million acre-feet of water per year. Releases of water from Glen Canyon Dam have always exceeded the upper basin’s delivery obligation of not less than 75 million acre-feet for any 10 consecutive years, pursuant to Article III(d) of the Colorado River Compact. Even during the drought of the early 2000s and lowered water storage in Lake Powell, Glen Canyon Dam was delivering flows above the upper basin’s Colorado River Compact commitment. There is no imminent prospect that this delivery obligation will not be met, and any change in the Colorado River Compact would require the resolution of numerous complex legal issues that could require many years or even decades to resolve. Nevertheless, the upper basin states intend to utilize a greater portion of their 7.5 million acre-feet per year allocation and, with rapid population growth in many areas, they continue to come closer to their full Colorado River Compact allocation. Future droughts and climate change may also affect precipitation and inflows into Lake Powell and other
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability storage facilities. Any shortages in water delivery obligations that resulted from climate change would be dealt with in the same way as shortages caused by drought or other factors. If changes in climate rendered the Law of the River inadequate to deal with resulting shortages, the Colorado River basin states could conceivably seek to amend the Compact and the United States and Mexico could conceivably seek an amendment of their 1944 treaty. Water releases from Glen Canyon Dam are a key issue at the hydrology-climate-population growth nexus in the Colorado River basin and bear close watching in the years ahead. One initiative that grew from the drought conditions of the late 1990s and early 2000s was the Department of the Interior’s Water 2025 program. The following excerpt comments on the Water 2025 program and touches on the water supply and demand issues discussed in this chapter: On the very first page of its 2003 report, “Water 2025,” the United States Bureau of Reclamation explains with chilling frankness that “today, in some areas of the West, existing water supplies are, or will be, inadequate to meet the demands of people, cities, farms, and the environment even under normal water supply conditions.” The report goes on to explain “the reality” that: “explosive population growth in western urban areas, the emerging need for water for environmental and recreational uses, and the national importance of the domestic production of food and fiber from western farms and ranches are driving major conflicts between these competing uses of water. The ‘major conflicts’ are occurring because most all of the surface waters in the region have been appropriated, leaving little for the continuing stream of newcomers” (Gavrell, 2005). Another critical issue is the prospect for transferring water from agricultural uses to help meet growing urban demands. Roughly 80 percent of the Colorado River basin’s water is allocated to the agricultural sector. Given limitations on constructing (and filling) new storage reservoirs, growing western cities are looking to agricultural water as a source of additional supplies. Municipalities often have a large willingness to pay for agricultural water rights, and both parties (i.e., agricultural sellers and urban buyers) often stand to gain by these types of transfers. There is a large amount of water held in agricultural water rights that could support a great deal of future urban
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Colorado River Basin Water Management: Evaluating and Adjusting to Hydroclimatic Variability population growth. There are barriers to transferring water to municipalities from agricultural and other users, such as tribal groups. These barriers include direct and third-party effects, and limited physical facilities for storing and rerouting water among willing buyers and sellers. As agricultural supplies are diverted to urban uses, this last remaining substantial amount of water that could be made available for urban uses in the Colorado River region is, slowly but surely, being depleted. Steadily rising population and urban water demands in the Colorado River region will inevitably result in increasingly costly, controversial, and unavoidable trade-off choices to be made by water managers, politicians, and their constituents. These increasing demands are also impeding the region’s ability to cope with droughts and water shortages. The drought of the early 2000s brought climate-related concerns to the fore across the Colorado River region. Not only did the drought result in numerous, direct hydrologic impacts, it raised questions about what climate trends and future conditions across the region and the planet might portend for Colorado River flows. The early 21st century also saw a great interest in several climate and hydrologic studies of the Colorado River region, especially several long-term reconstructions of past Colorado River flows that were based on studies of the annual growth rings of coniferous trees. The following chapter discusses how features of the global climate system affect the Colorado River region, temperature and precipitation trends and projections across the region, the gaged record of Colorado River flows, and studies of annual growth rings of coniferous trees (dendrochronology) and what they imply for regional hydrology and climate.
Representative terms from entire chapter: