February 22, 2007
It's All About Water, Stupid!
My Sustainable Natural Resources class went to Ankeny National Wildlife Reserve today to learn first hand about the management issues faced by the reserve. Our guide was a USFWS officer stationed at the Willamette Valley complex of reserves that focus on protection of Dusky geese and other migratory birds. She provided a first-class introduction to the Reserve, its resources, and management concerns. She described the population explosion of other Canada Goose sub-species, the challenge of managing migrating species with geologically distant breeding grounds, the ever present problem of poachers, finding the optimal balance given differing management regimes required for various species, etc.
She responded to my question about how USFWS is incorporating climate change impacts into its conservation planning by saying that they have a lot of taskforces...but, its really hard to do because we don't know exactly what's going to happen. That said, she went on to describe how her refuges are very water dependent and that regional climate change impacts may reduce water availability -- and some of the refuges have water rights and some don't.
Here's another account about how climate change will affect that most important and increasingly scarce Western resource: water. The National Research Council has just published its report on climate impacts on Colorado River basin Management. Though complete with the standard caveats, the most likely scenario is less water overall and more severe and frequent droughts. Here are some excerpts from the report brief:
Colorado River Basin Water Management:
Evaluating and Adjusting to Hydroclimatic Variability
Recent studies of past climate and streamflow conditions have broadened understanding of long-term water availability in the Colorado River, revealing many periods when streamflow was lower than at any time in the past 100 years of recorded flows. That information, along with two important trends—a rapid increase in urban populations in the West and significant climate warming in the region—will require that water managers prepare for possible reductions in water supplies that cannot be fully averted through traditional means. Successful adjustments to these new conditions will entail strong and sustained cooperation among the many entities involved in Colorado River water management and science programs.
This report from the National Research Council resulted from concerns regarding the long-term adequacy of Colorado River water supplies. Severe drought conditions have affected much of the region since the late 1990s, with 2002 and 2004 being among the 10 driest years on record in the upper basin states of Colorado, New Mexico, Utah, and Wyoming. Water storage in the basin’s reservoirs dropped sharply during this period due to very low streamflows; for example, 2002 water year flows into Lake Powell were roughly 25 percent of average.
During this same time period, there were several studies that produced “reconstructed” Colorado River flows over the past several centuries. These studies, based on data from annual growth rings of trees, show that there have been many past severe and extended droughts across the region. Just as important, they show that direct measurements of streamflow over the past 100 years, which have guided many administrative decisions for the river’s allocation and use, may offer an overly optimistic forecast of future water availability.
This report assesses existing scientific information—including temperature and streamflow records, tree-ring based reconstructions, and climate model projections—and how it relates to Colorado River water supplies and demands, water management, and drought preparedness.
Past Climate Information is Creating a New Water Management Paradigm
For many years, scientific understanding of Colorado River flows was based primarily on measurements of the river’s flow at gaging stations along the river. The first gaging stations on the river were established in the 1890s. As records of the river’s flow measurements accumulated through the years and as the number of gaging stations grew, a more complete understanding of Colorado River flows and variability emerged.
The Colorado River basin extends over seven U.S. states and parts of northwestern Mexico. For example, it is now known that the Colorado River Compact of 1922, which governs water allocations between the upper and lower Colorado River basin, was based on a short record of relatively high annual flows. Since the 1970s, the gaged record has been complemented by many different studies of past hydroclimate conditions. Some of these studies are based on indirect, or proxy, evidence of past climates. Some of these proxy studies are based on tree-ring data. Because annual growth rings in trees at lower elevations can reflect moisture availability, tree-ring data can be used to reconstruct records of past river flows. Using data from coniferous tree species with long life spans in the Colorado River region, flow records dating back several centuries have been reconstructed.
Past water management decisions have been based largely on the gaged record, and there has been an implicit assumption that there is a single value of the river’s average annual flow—about 15 million acre-feet/year—around which inter- annual flow variations occur. Even though the basin experienced wet and dry periods, river flows and weather conditions were expected to return to a “normal” state, largely defined by climate of the early and middle 20th century. However, recent tree-ring based reconstructions demonstrate that Colorado River flows occasionally shift into decadal-long periods in which average flows are lower, or higher, than the supposed mean value of 15 million acre-feet/year. These reconstructions reinforce the point that the gaged record covers only a small subset of the range of natural hydroclimatic variability in the river basin over several centuries. The basin’s future hydrology thus may not be reasonably characterized based on the gaged record alone.
Regional Climate Warming Points to Reductions in Water Supplies
Temperature records across the Colorado River basin and the western United States document a warming trend over the past century. These temperature records, along with climate model projections, suggest that temperatures across the region will continue to rise in the foreseeable future. Higher temperatures will result in less upper basin precipitation falling and being stored as snow, increased evaporative losses, and will shift the timing of peak spring snowmelt to earlier in the year. There is less consensus regarding future trends in precipitation. However, based on analysis of many climate model simulations, the preponderance of scientific evidence suggests that warmer future temperatures will reduce future Colorado River streamflow and water supplies. Reduced streamflow would also contribute to increasing severity, frequency, and duration of future droughts.
Increases in Urban Water Demand Will Stress Supplies
Rapid population growth across the western United States is driving increases in water demand. From 1990-2000, Arizona’s population increased by about 40 percent, while Colorado’s population increased by about 30 percent. Population projections suggest that this trajectory will continue. Although many innovative urban water conservation programs have reduced per capita uses, population growth is driving increases in urban water demands; water consumption in Clark County, Nevada (which includes Las Vegas), for example, approximately doubled in the 1985-2000 period. Steadily rising population and increasing urban water demands in the Colorado River region will inevitably result in increasingly costly, controversial, and unavoidable trade-off choices tobe made by water managers, politicians, and their constituents.
A significant trend in the quest to meet rising water demand has been the sale, lease, and transfer of agricultural water rights to municipalities, particularly in southern California and Colorado (in Arizona, tribal settlements, with transfers to municipalities, have also been important). With about 80 percent of western U.S. water supplies devoted to irrigated crop production, agricultural water appears to constitute the most important, and perhaps final, large source of available water for urban use in the arid U.S. West. Modest shifts of agricultural water to municipal and industrial uses can do much to help meet increasing urban water demands. At the same time, however, agricultural-urban transfers often entail “third party” effects that include costs for rural communities, ecosystems, and others indirectly dependent on water supplies affected by the transfers. Moreover, even though the amount of water allocated to western agriculture is large, it is finite, and thus there are limits on its ability to satisfy expanding urban water demands.
Technologies and Conservation May Not Fully Meet Future Demands
A wide array of technological and conservation measures can be used to help stretch existing water supplies. These measures include underground storage, water reuse, desalination, weather modification, conservation, and creative water pricing structures. These measures may not necessarily be inexpensive or easy to implement, but many of them show promise and will continue to be pursued and developed as water supplies tighten in future years. However, technological and conservation options for augmenting or extending water supplies—although useful and necessary—in the long run will not constitute a panacea for coping with the reality that water supplies in the Colorado River basin are limited and that demand is inexorably rising.
Sustained Collaboration Important for Better Drought Preparedness
Drought conditions have prompted the Colorado River basin states to move toward a new level of cooperation. This is illustrated by a February 2006 letter from the seven basin states to the U.S. Secretary of the Interior, which was written in response to a request that the states develop guidelines for coping with water shortages. The interstate cooperation and initiative exhibited in this letter represent a welcome development that will prove increasingly valuable—and likely essential—in coping with future droughts and growing water demands.
In addition to interstate cooperation, enhanced communication and collaboration between the scientific and water management communities will be vital. The knowledge base of Colorado River hydrology and climate rivals and may exceed comparable knowledge bases for any of the world’s river systems. Some of this information has been incorporated into key legal and operational decisions, but some of it may not be as well integrated in Colorado River basin water policy as it might be. A commitment to two-way communication among scientists and water managers is necessary for improving preparedness and planning for drought and other water shortages.
Warming, population hit Colorado River
PHOENIX - The 25 million Americans who rely on the Colorado River for water should expect continued — and even worsening — drought spells and water shortages as rising temperatures and growing populations create a double whammy, experts warned in a new report.
The experts, convened by the National Research Council, based their concerns on climate models and recent studies that found a cycle of droughts in the region over time. The studies used tree-ring histories to reconstruct local climate patterns over the last 500 years.
"These reconstructions, along with temperature trends and projections for the region, suggest that future droughts will recur and that they may exceed the severity of droughts of historical experience, such as the drought of the late 1990s and early 2000s," the experts wrote in the report released Wednesday.
The report said the region should expect higher temperatures that melt snow too early and allow too much runoff to evaporate.
"Temperature records across the Colorado River basin and the western United States document a significant warming over the past century," the experts noted. "These temperature records, along with climate model projections that forecast further increases, collectively suggest that temperatures across the region will continue to rise for the foreseeable future."
More than 25 million people in seven states — Arizona, California, Colorado, New Mexico, Nevada, Utah and Wyoming — rely on the Colorado River for water and power. The river also supports a diverse riparian system that has suffered as flows dropped.
'Trade-off choices' necessary
The report said the combination of threats could overwhelm the seven river states, which have struggled to produce a short-term drought plan.
The scientists did not propose specific policy changes, but urged Western water managers to work together on new ideas and prepare to make difficult decisions about how water is used.
"The basin is going to face increasingly costly, controversial and unavoidable trade-off choices," said Ernest Smerdon, a former dean of engineering at the University of Arizona and one of the report's authors. "Our hope would be that the community and the decision-makers will have planned before crises occur."
The experts noted that population pressure has added to the problem. Arizona's population grew by 40 percent in the 1990s, they noted, while Colorado's grew by 30 percent.
Water conservation measures have helped somewhat, but consumption has boomed in certain areas. For example, Nevada's Clark County, which includes Las Vegas, saw water use double from 1985 to 2000.
"The combination of limited water supplies, rapidly increasing populations, warmer regional temperatures, and the specter of recurrent drought point to a future in which the potential for conflict among existing and prospective new water users will prove endemic," the research council said in a statement that accompanied the report.
The report was commissioned by the U.S. Bureau of Reclamation, the Southern Nevada Water Authority and two California water agencies.
Growing cities will force states to strike more deals with farmers for water rights, but even that supply is limited, according to the scientists.
In addition, the report ruled out the idea of a solution built around conservation or water-saving technologies.
"Technological and conservation options for augmenting or extending water supplies — although useful and necessary — in the long run will not constitute a panacea for coping with the reality that water supplies in the Colorado River basin are limited, and that demand is inexorably rising," the experts wrote.
Much of the region has seen severe drought since the late 1990s, with 2002 and 2004 being among the 10 driest years on record in the upper basin states of Colorado, New Mexico, Utah, and Wyoming.
Water storage in basin reservoirs dropped sharply during that time due to very low streamflows, the experts noted. For example, 2002 water year flows into Lake Powell were roughly 25 percent of average.
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