Cities across the United States anticipate significant water challenges caused by climate change and are updating their water management plans to address areas of vulnerability and prepare for the worst.

“Future demand is always the biggest challenge,” says Ellen Levin, deputy manager for San Francisco Water Enterprise (SFWE), a division of the San Francisco Public Utilities Commission that provides water service to 2.5 million people in the Bay Area, including 27 other municipalities.

Climate models project California to be up to 5.4 degrees Fahrenheit warmer by midcentury and 9 degrees warmer by 2100, according to a report by the Natural Resources Defense Council (NRDC), Climate Change, Water, and Risk, which maps areas at high risk for water shortages. SFWE’s plan would meet at least 80 percent of water demand during a drought lasting eight and a half years—the length of the last two droughts combined.

“We’re implementing more conservation to reduce reliance on rainfall or snowpack,” she says. Per-capita water use in SFWE’s service area has dropped from 107.5 gallons (407 liters) per day in 1981 to 80 gallons (303 liters) now, a decline largely achieved through conservation measures that include expansion of a separate wastewater recycling system and financial incentives for installing water-saving technologies and irrigation systems.

 kirk_1_351A rise in sea level of up to 55 inches by the end of the century would have a devastating impact on the regional, national, and global economies, as well as put the ports of Long Beach and Los Angeles under water.

“We’re now in a mode of analyzing vulnerability of water supply due to changes in climate,” adds Levin. “We’re taking a systems approach, using scenarios from global climate models to determine changes in inflow we can expect to our reservoirs and what changes we can make in infrastructure to improve sustainability of supply.”

But drought is not the only threat to water supply posed by climate change. San Francisco is among several major U.S. coastal cities—others are New York City, Los Angeles, Seattle, and Miami—expected to experience flooding of infrastructure and critical facilities as well as saltwater intrusion into freshwater resources as sea levels rise.

The sea level on the West Coast is expected to rise 12 to 18 inches (30 to 45 cm) by mid-century from 2000 levels, and 20 to 55 inches (50 to 140 cm) by the end of the century. Rising sea levels could inundate critical infrastructure in the Bay Area, including power plants, roadways, railways, airports, and the Port of Oakland. More than 640 miles (1,030 km) of new levees or seawalls, estimated to cost more than $5 billion, are needed to protect the area against flooding from a 55-inch rise in sea level, according to a separate NRDC report of water-related vulnerabilities in 12 major cities.

A 55-inch rise in sea level could be even more devastating for Los Angeles County, doubling the number of hazardous facilities at risk from a 100-year flood, including superfund sites, generators of hazardous waste, wastewater treatment plants, and brownfield properties. This means flooding could contaminate water supplies, as well as disrupt the operation of power plants and other infrastructure critical to the economy.

Still, drought is the most serious and immediate concern. The Sierra Nevada keeps a significant portion of southern California’s water supply on ice until needed, but an ongoing analysis by Los Angeles Department of Water and Power (LADWP) indicates that global warming is already melting snowpack early. This could mean longer dry spells in late summer and greater potential for drought.

In addition, modeled projections indicate that precipitation will decrease in arid regions of the Lower Colorado River basin, a major water source for California, Nevada, Arizona, and Mexico, according to a report by the U.S. Department of Interior’s Bureau of Reclamation. Southern California’s allocation of Colorado River water is 58 percent, or 4.4 million acre-feet annually. (One acre-foot equals about 326,000 gallons [1.2 million liters].) Studies indicate river flow will decline by 6 to 20 percent by the mid–21st century, but the risk of shortages for users in the Lower Colorado River basin is expected to increase about 40 percent by 2026 because of a decrease in decrease in precipitation and snowpack over time.

Water supply has always been a top priority for Los Angeles, and LADWP, which serves more than 4 million residents of the city and adjacent municipalities, has worked hard at conservation. Conservation strategies, including water use restrictions, a tiered rate system, and financial incentives for installing water-efficient technologies and landscaping, resulted in water use today dropping below 1979 levels, despite a population increase of more than 1 million.

LADWP also is collaborating with regional utilities to develop the Greater Los Angeles Integrated Regional Water Management Plan. The plan is a blueprint for facilitating regional cooperation to address water resource needs and compete for state funding of water-related infrastructure, says Kerjon Lee, spokesman for Los Angeles County Waterworks (LACW), which serves about 200,000 county residents. This long-range plan will identify regional issues related to climate change and create partnerships to deliver mutually beneficial solutions to water-related problems.

Southern Nevada may face even greater water supply challenges than southern California. Ninety percent of the region’s water supply comes from the Colorado River, but the state’s allocation is only 1.8 percent of the total because when the river water was divvied up in 1928, Nevada’s population was only 10,000.

The 300,000 acre-feet of water provided annually is sufficient to meet current demand—227,000-acre feet—but there is concern about the future, says J.C. Davis, spokesman for the Southern Nevada Water Authority (SNWA). The Las Vegas Valley is the fastest-growing region in the nation, adding about 5,000 people per month and seeing its population double every decade. The influx of new residents slowed with the economic downturn, but the region’s population is now nearly 2 million and is projected to exceed 3.6 million by 2035.

 kirk_2_250Adjacent to Hoover Dam, Lake Mead serves as a reservoir for the Lower Colorado River, which supplies water to Nevada, California, Arizona, and Mexico.

Conservation has been the area’s saving grace. Initiatives implemented over the past decade reduced water demand by 32 million gallons (121 million liters), despite the addition of nearly 1 million residents, Davis notes. Much of the credit goes to a regional water recycling system that operates at 100 percent efficiency. “Virtually every drop [of water] used inside homes, hotels, and restaurants is recycled,” he notes. “What matters here is outdoor water use. The vast majority of water used is for landscaping residences because everyone brings ‘a little bit of Indiana’ with them.”

SNWA is focused on reducing outdoor water use, offering a cash rebate of $1.50 per square foot ($16 per sq m) of grass lawn replaced with drought-tolerant landscapes. The program has already removed 155 million square feet (14 million sq m) of grass, enough to lay a roll of sod three-quarters of the way around the world, notes Davis.

Meanwhile, the amount of water in Lake Mead, the Las Vegas Valley reservoir, is an ongoing concern. The lake’s water level last year had fallen 52 percent after a decade-long drought, when SNWA began digging a third intake tunnel deeper in the lake to provide a cleaner, more reliable water supply.

Arizona receives more than 37 percent, or 2.8 million acre-feet, of Colorado River water. The Greater Phoenix and Tucson areas get about half the state’s allocation—1.5 million acre-feet. The Phoenix area also receives a 44 percent allocation from the Salt River Project (SRP), which conveys surface water from Salt River and Verde River watersheds to the north and east.

“We’re always monitoring supply, looking at cycles,” says Gerard Silvani, principal planner for the Phoenix Water Services Department. “The earliest we expect to see a shortage is 2020.” Lower water demand has allowed the city to store some of its water allocations underground for future use, he notes.

Through conservation, the Phoenix area’s water use has remained unchanged at 300,000 acre-feet for the past 20 years despite the population increase from 971,000 to nearly 1.5 million. Silvani notes that in 1990, per-capita water use was 240 gallons per day (910 liters), but now is 180 gallons (680 liters).

Tucson, with a population of 740,000, gets 134,000 acre-feet from the Colorado River, but only used 109,000 acre-feet of water last year, down from 115,000 acre-feet a few years ago, the decline attributable to slowing growth. Like Phoenix, Tucson takes its full water allocation and stores the unused portion in an aquifer.

“There is no concern of shortage right now,” says Fernando Molina, spokesman for the Tucson Water Department. “We do a good job of maintaining water supply and are in a better position than most Southwest cities because we still have a supply of backup groundwater.

“But we are looking into the future and taking a hard look at how climate change might affect supply,” he continues. The city is focused on expanding its water reclamation system and updating infrastructure. “Our objective is to save water by using renewable supplies,” Molina says. Developers are required to install a secondary plumbing system in new homes and commercial buildings to provide access to graywater supply, he notes.

San Antonio, Fort Worth, and Dallas, three Southwest cities at very high risk for water shortages, are employing innovative solutions to ensure future supply.

San Antonio, a city of 1.3 million, is 20 years ahead of schedule on implementing a 50-year water management plan, says Greg Flores, spokesman for the San Antonio Water System (SAWS). Hallmarks of the plan include constructing the Twin Oaks Aquifer Storage and Recovery facility, which stores the city’s unused water allocation in an environmentally friendly bubble in a separate aquifer.

The city gets a 45 percent allocation, or about 257,000 acre-feet, from the Edward’s aquifer, a regional water source. “In wet years, we pump all the permitted water not used. That’s how we roll it over,” says Flores. Stored water met 2 percent of the city’s water demand during the drought last summer. The storage aquifer holds 90,000 acre-feet of water, representing half of the city’s total annual demand.

In addition, a pipeline will begin transporting water from neighboring Gonzales County in 2013, and a new desalination plant, which is designed to bring brackish groundwater up to drinking-water quality, will come on line in 2016. The utility is also studying the possibility of building a pipeline to transport ocean water to a desalination facility.

Aggressive conservation strategies have already lowered San Antonio water demand to the same level as 25 years ago, even though the customer base has grown 67 percent.

The city has one of the nation’s largest recycled-water systems, with 100 miles (160 km) of pipeline delivering highly treated, recycled water for irrigation and cooling to public facilities and commercial customers throughout the city.

The utility also offers free water-efficient toilets, financial incentives for water-saving technologies and landscaping, and free plumbing retrofits to schools and businesses. Since the program’s inception in 1995, the city has distributed 24 million high-efficiency toilets.

Experiencing one the region’s worst droughts ever last summer, north Texas cities have joined forces to shore up future water security, notes Linda Christie, director of community and government relations for the Tarrant County Water District (TCWD).

TCWD, which serves the Fort Worth area, is sharing with Dallas the cost of building a $2 billion pipeline and water recycling system. The pipeline will connect the Trinity River, which runs through both cities, with reservoirs south of Dallas and create a new lake in Dallas. The project calls for 1,200 acres (485 ha) of wetlands around the reservoirs to naturally clean wastewater collected by the Trinity River. This natural wastewater treatment system will return an estimated 115,000 acre-feet of water to the region’s water supply. “In essence, we get another reservoir just by putting a reuse system in place,” Christie says.

Though uncertainty may exist about how quickly or severely climate change will affect water supplies, “It will involve too much or too little water,” warns Theo Spence, a senior advocate for the NRDC and editor of Climate Change, Water, and Risk.

While drought-prone areas of the West, Southwest, and Great Plains are likely to experience extreme water shortages, the East Coast, Pacific Northwest, upper Midwest, and Great Lakes regions will experience an increase in precipitation and increasingly powerful and frequent storms.

A comprehensive assessment of the impact of climate change on Washington state, prepared by the University of Washington’s Climate Impacts Group, identified Seattle’s vulnerabilities to climate change. A predicted steady rise in temperature of 2 degrees F by 2020 and 5.3 degrees by 2080 would increase the frequency of severe storms, which, along with a rise in sea level, could result in flooding of homes, transportation networks, and other infrastructure.

Warming would also change the timing of precipitation and snowmelt in the Central and Northern Cascades—the source of Seattle’s water supply. This would create a challenge for supply managers balancing the need for potable water in summer with adequate supply for hydroelectric facilities, shipping locks, and wildlife habitats. It also would raise stream temperatures, increasing the frequency and duration of harmful algal blooms that kill salmon and other fish and contaminate shellfish.

The Washington state report is helping city officials understand the potential consequences of climate change and develop adaptive strategies to overcome challenges. The city has already developed tools to monitor weather changes and assess how climate change could affect new developments and infrastructure.

In Chicago, scientific modeling indicates the city will see a 5 to 10 percent increase in precipitation by 2039 and a 20 percent increase in the second half of the century. The frequency of heavy downpours of more than two and a half inches (6.3 cm) of rain in 24 hours are likely to increase 50 percent between 2010 and 2039 and 80 to 160 percent by 2100, according to the NRDC report on Chicago. The average temperature in the Chicago area is expected to rise about 2.5 degrees F by 2039 and up to 9 degrees by the end of the century.

Spence notes that Chicago’s water supply, which comes from Lake Michigan, is at high risk of contamination because the city’s combined sewage and stormwater collection system discharges a mix of untreated sewage and stormwater into the Chicago River and Lake Michigan when rainfall exceeds 0.67 inches (1.7 cm) in 24 hours.

To help mitigate the problem, the city adopted an ordinance increasing the amount of permeable area required for new development and installed 120 green alleys—with more than 32,000 square feet (3,000 sq m) of pervious surface area—to allow rain to infiltrate groundwater and thereby decrease runoff. The city also is developing a wastewater modeling system to evaluate infrastructure performance under different weather conditions and identify vulnerable areas.

In New York City, sea level could rise up to 29 inches (74 cm) by midcentury, sending saltwater farther up the Hudson and Delaware River estuaries during high tide. A rise in temperature of 3 to 5 degrees F would also increase evapotranspiration—water loss through evaporation and vegetation transpiration—promoting growth of certain infectious microorganisms and pathogens in recreational waters.

In addition, an annual increase in precipitation would include more frequent and powerful storms. Coastal flooding associated with these storms and a rise in sea level would affect major transportation networks and the viability of waterfront structures, including expensive real estate at the southern tip of the financial district.

Responding to such reports, Mayor Michael Bloomberg established a panel of experts to advise him on issues related to climate change and provide support to a task force charged with developing adaptation strategies.

Boston, situated along the coast with concentrated development along riverbanks and coastal shorelines, is also at high risk for severe flooding caused by increasing precipitation, more frequent and intensifying storms, and a rise in sea level of up to 3.3 feet (1 m) by the end of the century. Flooding would affect transportation and other infrastructure, waterfront real estate, and water quality, according to the NRDC report on Boston, which indicates flooding of wastewater treatment facilities would increase the concentration of pathogens washing onto beaches and into rivers.

Prompted by a 2004 analysis of the socioeconomic impacts of climate change on the Boston metro area, the city adopted policies to require consideration of climate change in planning new municipal facilities and major renovations, as well as improvements to sewer and stormwater systems.

Meanwhile, cities farther south are worried about too little rain.

Atlanta a few years ago felt the brunt of severe drought, which also affected Florida and Alabama. Georgia Governor Sonny Perdue blamed the drought on the U.S. Army Corps of Engineers for releasing more than 20 billion gallons (70 billion liters) of water from Lake Lanier to address a faulty gauge at the dam; the lake supplies water to the three-state region and is the source of 40 percent of Atlanta’s water.

Over the past few years, Atlanta has implemented a long-term water management plan that calls for aggressive conservation, six new reservoirs, upgrades of water management facilities, and use of recycled water. “Our plan provides for adequate water supply for the next 30 years,” says Pat Stevens, chief of environmental planning for the Atlanta Regional Commission. She admits, however, that rainfall is the big unknown.

Annual rainfall in southeast Florida is likely to decrease 10 to 20 percent in the coming decades, according to the NRDC. Meanwhile, temperatures in the Miami region are expected to rise 4.5 to 9 degrees F by midcentury, which will increase the frequency and duration of heat waves and the risk for drought.

The frequency and intensity of storms, including hurricanes, will also increase, putting the region at high risk for storm surges and flooding exacerbated by higher sea levels. With an average elevation of six feet (1.8 m), Miami assets are highly vulnerable to sea level rise, which is predicted to be 1.5 to 2.3 feet (0.5 to 0.7 m) by midcentury and 3 to 5 feet (0.9 and 1.5 m) by 2100. In fact, Miami is ranked number one worldwide in terms of population and assets exposed to coastal flooding in a study by the Organization for Economic Cooperation and Development.

A higher sea level is expected to cause saltwater intrusion into estuaries, wetlands, and tidal rivers, and threaten the Biscayne aquifer, Miami’s main source of drinking water. Many of Miami’s sandy beaches and parts of the nearby Everglades, including sensitive wildlife habitats, are expected to be underwater by midcentury.

Southeast Florida officials recognize the region’s precarious situation and are investing extensive resources in planning for the impacts of climate change. The Southeast Florida Regional Climate Change Compact, a cooperative effort of Miami-Dade, Broward, Palm Beach, and Monroe counties, calls for coordination of policy positions, scientific research, and adaptation and mitigation efforts. The group also is leveraging the counties’ resources to assist federal agencies involved in monitoring and mitigating the impacts of climate change.

While some cities are updating their water management plans to address areas vulnerable to the impacts of climate change, many others still are looking to the past to plan the future. But Spence warns that assumptions based solely on past events are no longer valid. “Climate change must be factored into scenarios,” he says. “Not to do so is irresponsible and nearsighted.”

Failing to do so also could affect a city’s bond rating. A report from Ceres, a Boston-based environmental research and sustainability group, provides information to aid bond-rating agencies in evaluating local governments and public utilities in terms of their understanding and management of the potential risks of water undersupply. The report encourages investors to seek information on environmental risk that is material to the present and future value of investments.

“Cities sold bonds based on their need for infrastructure to move, clean, and supply water, but credit ratings agencies may not have taken drought issues into account at the level that they should,” notes an analysis of the Ceres and NRDC reports by 24/7 Wall Street, a watchdog for the bond sector. “Extreme disruptions of the water supply of any city would have severe financial consequences.”