As climate-related disasters pose increasing effects, how can property owners, designers, and decision makers help reduce risk and bolster resilience? Landscape-based strategies are proving their value for mitigating short-term weather crises and alleviating chronic stresses. Such cost-effective solutions bring multiple benefits, but they require a new view of the functional role of landscape as a tool rather than decoration, as well as a thorough appreciation of the vulnerabilities inherent in each specific project and place.
Landscapes That Bounce Back
ULI’s 2018 publication Ten Principles for Building Resilience defines resilience as “the ability to prepare and plan for, absorb, recover from, and more successfully adapt to adverse events.” Resilience stands alongside but distinct from sustainability: while sustainable practices can be viewed as the “software” of designing and building in ways that minimize use of resources, resilient design relates more strongly to the “hardware” of infrastructural and community frameworks.
Landscape architecture fosters resilience through site-sensitive approaches to land use planning, mobility networks, grading and flood control, water management, revegetation, and open-space design—in short, by integrating designed systems within the dynamics of natural systems.
In their 2013 book Landscape Infrastructure, SWA principals Ying-yu Hung and Gerdo Aquino illustrate how landscape can be leveraged as an instrumental part of the processes of city life. “Can landscape itself be considered infrastructure, when acting as a . . . network capable of moving people and supporting a variety of living systems?” Aquino asks. He and Hung argue that the answer is a definitive yes.
By addressing the interstitial spaces that underlie contemporary cities, such as drainage corridors and street systems, landscape-based infrastructure can augment traditional civil-engineered systems, foster health and wellness, and support resilience at a variety of project scales.
Designed to Flood
In August 2017, Hurricane Harvey dropped an estimated 27 trillion gallons (102 trillion liters) of rain on metropolitan Houston in less than a week. Floodwaters surged into the city’s signature open space, Buffalo Bayou Park, which initially retained the water. Once the water receded, the park was left with 40,000 cubic yards (31,000 cu m) of silt and debris. Yet within days, Houstonians were back on the trails, bike rentals had resumed, and restaurants had reopened for business.
“Buffalo Bayou Park has been a national model for resilience, surviving three major floods, including Harvey,” says Katharine Burgess, senior director of ULI’s Urban Resilience Program. “Cities across the country are looking to invest in flood infrastructure . . . that does double duty by improving quality of life and recreation opportunities, and increasing preparedness for extreme events.”
The park, designed by SWA’s Houston office and awarded a ULI Global Award for Excellence in 2017, offers an array of replicable strategies. All lighting, plantings, and walkways are designed to withstand submersion and the impact of floating debris. Channel configuration enhances the bayou’s natural meanders to slow floodwaters. Silt benches—areas where the bank is flattened and graded to an elevation just above the typical water elevation to collect silt during a flood—have been created to facilitate predictable deposits located where silt is easily collected. At the same time, the 160-acre (65 ha) public space supports a robust program of pedestrian and cyclist access and includes event lawns, protected gardens, nature play areas, and flexible plazas that bring together Houston’s diverse population.
In Houston’s Clear Lake neighborhood, the new Exploration Green park also demonstrated its resilience last year. The first of the project’s five phases was only 80 percent complete when Hurricane Harvey arrived. Nonetheless, the 178-acre (72 ha) greenway—converted from a former golf course—amassed enough floodwater to spare 150 or more residences. Scheduled for completion in 2021, the greenway will ultimately include a series of detention ponds with an estimated 500 million–gallon (1.9 trillion liter) capacity.
In Long Island City, New York, the design for Hunters Point South Waterfront Park proved its ability to withstand Superstorm Sandy before the park even opened to the public. Landscape was under construction when the storm hit in October 2017.
As envisioned by the team of Thomas Balsley Associates, Weiss/Manfredi, and Arup, the project effectively detained floodwaters within a bowl-shaped central green designed to drain back to the river. The bowl’s synthetic turf withstood saltwater immersion at a depth of nearly four feet (1.2 m) and will allow the park to bounce back in the face of future storms and rising sea levels. Newly planted honey locust trees and an engineered-plank promenade also escaped the storm unscathed.
Sea-level rise represents a more gradual but no less ominous threat to the built environment. New York’s SCAPE Studio is examining adaptive strategies to address sea-level rise, following on its work for the Museum of Modern Art’s 2010 Rising Currents exhibition. Oysters—for which New York was once famous—inspired the studio’s plans.
The mollusks filter bacteria as part of their normal biological processes, and their three-dimensional colonies, if undisturbed, accrete into massive underwater structures that can break up large waves before they reach the shore, reducing erosion. SCAPE’s “oyster-tecture” proposes installing oyster larvae–seeded rope nets above the seafloor to prevent the organisms from becoming covered with silt. These hybrid natural/artificial breakwaters are currently being designed for the south coast of Staten Island, which was hit especially hard by Superstorm Sandy.
Wildfire and Drought
Inland communities face other climate-related challenges. For example, 2017 is on record as the worst ever for wildfires. In northern California, firestorms damaged or destroyed more than 15,000 homes, business locations, and other structures in October; extreme wildfires in early December burned hundreds of homes in Los Angeles.
Together, these disasters inflicted $18.2 billion of damage and claimed 54 lives.
Other wildfires across the western states burned over 9.8 million acres (4 million ha), exceeding the ten-year annual average of 6.5 million acres (2.6 million ha). Montana, in particular, was affected by wildfires that burned over 1 million acres (405,000 ha)—and severe droughts in these areas have left swaths of landscape as dry as tinder.
Recent devastation makes clear that fire-resistant building materials and emergency reservoirs are not sufficient safeguards. The American Society of Landscape Architects (ASLA) points out that protection and suppression costs in the United States have more than tripled since the 1990s, surpassing $3 billion a year—indicative of bigger fires and a greater threat to communities. Rising temperatures and drought make it easier for fires to start, and suppression of localized blazes in fire-prone areas has resulted in increased growth of underbrush under the tree canopy, which provides fuel for more intense fires and greater risk of large-scale erosion.
Landscape-based solutions can mitigate these hazards. Smart planning and site selection are critical: some areas may simply be too fire-prone to be developed. For established communities, new technologies include remote sensors to track humidity, wind, temperature, vegetation density, and water availability, with alerts sent during highest-risk periods. Projects can incorporate “defensible spaces” or fire breaks to fend off fires, and prescribed burns can alleviate the threat of larger, uncontrolled fires.
The time-honored practice of purposeful plant selection remains a key strategy. Shady Canyon, a 1,070-acre (433 ha) residential community in Orange County, California, lies in a high-fire-hazard area. Designers at SWA’s Laguna Beach office addressed the threat by eliminating plants with high fuel volumes, instead using native oaks, toyons, and sumac, known for their resistance to fire, on the outskirts of the development. Native plants are more fire resistant, so they reduce wildfire risk while increasing biodiversity.
Heat stress, a recurrent health problem for city residents, is a leading weather-related cause of death in the United States. Higher temperatures are amplified by the urban heat-island effect—the buildup in cities of zones that are hotter than nearby rural areas because of the prevalence of paved surfaces and reduced vegetation.
Landscape strategies to reduce urban heat islands include increased tree cover, green roofs, and the use of cool—reflective or permeable—pavement materials. Vegetation lowers surface and air temperatures by providing shade and evapotranspiration; shaded surfaces may be 20 to 45 degrees Fahrenheit cooler than the peak temperatures of unshaded materials. Landscape plantings are most effective when installed in strategic locations around buildings—for instance, with deciduous trees or vines located on western exposures for shading windows and roofs—or when shading pavement in parking lots and on streets.
Arizona’s cities illustrate some of the highest impact of the heat-island effect. Phoenix, for example, sees temperatures as much as 21 degrees hotter in the city than in nearby rural areas. In Tucson, Mayor Jonathan Rothschild’s 10,000 Trees program aims to reduce heat stress through citywide urban forestry.
Jaimie Galayda, sustainability policy adviser in the Tucson Mayor’s Office, points to the benefits of combining tree planting with stormwater measures. “Our community is supportive of rainwater harvesting because it improves our quality of life,” she says. “A place that offers shade is more walkable, and those types of spaces are visually distinct and inviting. That’s where people want to gather.”
Tucson’s initiative, which has yielded 20,000 new trees to date, began with mapping the existing tree canopy to identify “shade priority areas.” Not surprisingly, less-affluent neighborhoods exhibit a more sparse tree canopy, making them more vulnerable to heat-island impacts—a situation that calls for efforts to protect people in lower-income neighborhoods from heat stress.
Urban tree-planting programs have proved the value of greening up the city: in short, trees pay their way by increasing property values and reducing energy costs for cooling. Economists at the University of Washington determined that the presence of large trees in yards and street trees can add 3 to 15 percent to home values throughout neighborhoods, while retail customers indicate they will spend 9 to 12 percent more for goods and services in central business districts that have a high-quality tree canopy.
On a smaller scale, urban parks foster economic resilience while providing social and cultural benefits. Detroit’s 1.6-acre (0.65 ha) Campus Martius, designed by Rundell Ernstberger Associates, offers an inspiring prototype. When the Detroit 300 Conservancy set out to build Campus Martius in 2000, there was little activity in the district; since then, the city has seen more than $3 billion of investment on the park’s perimeter.
In Tulsa’s emerging downtown arts district, Guthrie Green transformed a 2.6-acre (1 ha) truck yard into a lively community space that draws upward of 3,000 people weekly for a wide variety of activities. Developed and operated by the George Kaiser Family Foundation, with design by SWA’s Sausalito office, the park has catalyzed investment in a neglected industrial area. The project incorporates an underground geo-exchange system that reduces energy costs for nearby nonprofit arts centers.
Built landscapes are also powerful tools for fostering stewardship of urban environments. In Monterrey, Mexico, SWA San Francisco’s master plan for the Universidad de Monterrey restored a hot, unshaded, car-oriented campus as an artful expression of native landscape. New pedestrian connections encourage walking, while indigenous plants—combined with water retention and filtration—replaces ornamental planting, resulting in a 38 percent reduction in water use for the landscape. The university’s president expressed his gratitude for the transformation in a way that struck home: he said the project had restored the Monterrey of his childhood.
At a variety of scales, for a wide range of projects and challenges, landscape-based strategies enable developers and cities to reduce risk, adapt to incremental change, and bounce back from disasters. Adopting these strategies as part of projects can forge economic, social, and cultural benefits, yielding additional value. Now more than ever, the tools of landscaping should be deployed to perform as part of our infrastructure, offering multiple pathways to a shared, resilient future.
ELIZABETH SHREEVE is an urban planner and designer with over 30 years of experience in land use, landscape architecture, and site restoration. She is a planning principal in SWA Group’s San Francisco and Sausalito studios and chair of ULI’s Sustainable Development Council.