This week’s UGEC Viewpoints article marks the beginning of a four-part series focused on urbanization and global environmental change research at the Julie Ann Wrigley Global Institute of Sustainability, the host institute of the Urbanization and Global Environmental Change Project.
It is co-curated by UGEC Scientific Steering Committee member Christopher Boone, Dean of the Arizona State University’s School of Sustainability and Mark Watkins, Co-Editor of UGEC Viewpoints.
Arizona State University, USA
Urban design professionals (i.e., landscape architects, urban planners, architects, civil engineers, etc.) suffer from two interconnected design problems related to reducing urban heat islands (UHI): incomplete human scale knowledge and lack of metrics to measure design outcomes. Even though urban design is only one part of a continuous cycle of land management (see figure 1), designers are key authors of our urban climate. Designs, once constructed, lock landscapes into certain urban climate trajectories, some hotter than others. Increasingly cities’ incentivize or require designers to include cool infrastructure strategies at the site and urban design scale (human scale). The U.S. Environmental Protection Agency’s (EPA) categorizes these cooling strategies as cool roofs, green roofs, trees and vegetation, cool pavements, and smart growth. These strategies are designed to reduce urban heat, some probably do, but others may actually enhance urban heat in cities because our knowledge of human scale heating processes is incomplete (Erell et al., 2013).
UHIs are urban hotspots that intensify hot weather and increase residents’ exposure to heat. These hotspots are unintentionally designed by constructing landscapes with large proportions of impervious buildings and pavement (Coseo and Larsen, 2014a). UHIs are seen as a growing problem for the sustainability of cities, particularly in light of rising regional air temperatures associated with climate change (Stone, 2012). Cities are concerned because UHIs are associated with negative health outcomes, increased resource use, and decreased quality of life (Gartland, 2008; O’Neill et al., 2005; Harlan et al., 2006; Stone, 2012). Researchers provide some good direction to designers on cooling strategies (Erell et al., 2012). Nevertheless, researchers struggle to devise useful human scale guidance for design because in the past many UHI studies have been at too coarse a scale. When cooling strategies are implemented, cities don’t really know if designs are performing as intended. Yet, this incomplete knowledge or lack of metrics has not stopped cities from investing in cooling strategies.
|Table 1: US EPA Heat Island Initiative Types|
|Air Quality Requirement||Outreach and Education Program|
|Building Standard / Energy Code||Research|
|Climate Action Plan||Resolution|
|Comprehensive Plan and Design Guidelines||Tree and Landscape Ordinance|
|Demonstration Project||Urban Forestry Program|
|Green Building Program and Standards||Weatherization|
Governments spend considerable resources constructing cooling strategies. This investment in cool infrastructure will only accelerate as heat management (Stone, 2012) becomes more widely implemented. According to the EPA’s Urban Heat Island Community Actions Database, the U.S. has over 75 local and state initiatives to enhance cool infrastructure. The initiatives fall under at least 16 different policy mechanisms to build additional cool infrastructure (see table 1). The hope is that designers may incorporate place specific strategies to alleviate UHIs and thus exposure to heat. I argue that two coupled trends are improving how designers address heat: 1) a move toward human scale urban climate research, and 2) the expansion of performance metrics into design practice.
Human scale urban climate research
Identifying and communicating the drivers of urban heat at the human scale for design applications is a tricky problem for researchers. In fact, it really wasn’t until the 1980s that urban climate researchers began to target designers as an audience (Arnfield, 2003; Oke, 1984; Oke, 1988). Luckily, researchers have made progress toward better design guidance. Hough (2004), Gartland (2008), and Erell et al. (2012) provide more useful guidance aimed at a design audience. Three key trends over the last 20 years include more rigorous guidelines for research, innovative instrumentation, and inclusion of vulnerability frameworks.
The first trend has been for urban climatologists to develop more rigorous instrumentation siting and improved guidance for quantification of a site’s physical characteristics. Stewart’s (2011) review of 190 UHI studies from 1950-2007 found at least half were “scientifically indefensible” and two-thirds failed to describe siting of instrumentation and a site’s physical characteristics. To address these types of concerns, the World Meteorological Organization released The Guidance to Obtain Representative Meteorological Observations at Urban Sites (Oke, 2006). It provides best practices for siting weather observation equipment in urban conditions. I used Oke’s (2006) techniques with a colleague (Coseo and Larsen, 2014a) for siting weather stations to isolate the drivers of heat in eight Chicago neighborhoods. We found that the drivers of urban heat vary by time of day and weather conditions, making recommendations for simple design strategies more complicated. At night, the percentage of impervious surfaces was the biggest contributor to UHI, while during the day it was distance to upwind industrial areas. We found human scale cooling strategies may have more localized effects at night than during the day due to calmer winds at night. Stronger winds during the day may complicate heating processes making selection of cooling strategies problematic.
Along with improved siting, Stewart and Oke (2012) released Local Climate Zones (LCZ) for land classification and to improve quantification of a site’s physical characteristics. LCZ is a classification approach to spatially group landscapes with similar physical characteristics. LCZ is a major step forward in conceptually linking urban climate with design. These advances in urban climate research will create knowledge relevant and transferable to design. We (Coseo and Larsen, 2014b) also examined the same data as the previous study using the LCZ framework to compare approaches and found some problems in operationalizing the LCZ classification. Although still immature, the LCZ concept promises to help incorporate urban climate monitoring into smart city data networks, such as Chicago’s effort to monitor everything from the Divvy bike share to green roofs to crime. This trend toward human scale research opens new paths for researchers to partner with designers and cities on urban climate issues.
Figure 2: Chicago Green Alley Program performance evaluation using a custom designed weather tricycle. Image source: Paul Coseo
The second trend has been for researchers to combine mobile, in-situ stationary, and remotely sensed instruments to better understanding urban climates. We (Coseo and Larsen, 2015) evaluated the performance of Chicago’s Green Alley Program, a cool pavement program, using a custom designed weather tricycle (figure 2), in-situ weather observations (figure 3), and remotely sensed data. We found that the green alleys with high albedo and porous pavement did not have significantly cooler air temperatures at night when compared to nearby control alleys with conventional asphalt. Our findings suggest that high albedo and porous pavements alone are not enough to overcome the complicated heating contribution from ground and wall elements in compact urban spaces. Although cool pavements may work in urban spaces dominated by those technologies, it may not be sufficient to reduce air temperatures in locations where it only represents a small proportion of the built features. This type of human scale research approach promises new insight into the design of cooling strategies.
Figure 3: Locating stationary weather instruments on utility poles in Chicago for the Chicago Green Alley Program research project. Image source: Paul Coseo
The final critical development over the past 20 years is to contextualize and humanize the examination of UHIs by including issues of public health and equity. Linking heat to social aspects is critical to making guidance relevant for equitable and sustainable design applications. Vulnerability frameworks have assisted researchers in prioritizing the siting of instruments within metropolitan areas to demonstrate the inequitable distribution of heat hazards. In Phoenix, Harlan and colleagues (2006) found that lower income neighborhoods were more vulnerable to heat because they had less capacity to afford plant material or irrigate it than wealthier neighborhoods. Vulnerability frameworks offer designers a new lens to address environmental justice through design by prioritizing vulnerable neighborhoods for cooling strategies.
Performance metrics in design practice
Designers are working to integrate landscape performance metrics into the design process for cooling strategies using an ecosystem services framework (Steiner, 2014). The Landscape Architecture Foundation (LAF) defines landscape performance broadly “…as a measure of the effectiveness with which landscape solutions fulfill their intended purpose and contribute to sustainability”. The intent of performance metrics is to improve design decisions, while also providing evidence of desirable outcomes. Although not a new concept, landscape performance may offer a path toward creating more sustainable urban systems. Even so, designers must cautiously use ecological service frameworks to ensure they don’t overlook the complex interrelationships within ecological systems (Norgaard, 2010). Steiner (2014: 306) raises a critical question, “[h]ow do we account for ecosystem services which cannot be monetized or have little value to humans?” We must ensure both qualitative and quantitative analyses are valued to avoid compartmentalizing ecosystem functions. In spite of criticisms, this form of evaluation is becoming an institutionalized method of evaluating performance for cooling strategies.
Landscape performance has emerged from both the sustainability and ecosystem services narratives for evaluating design strategies. In 2000, the LEED certification system was established, which aims to construct more sustainable buildings. Many cities have integrated LEED into the formal urban design process. Chicago incentivizes developers to use LEED through their Green Permitting Program, which significantly reduces the time to receive a building permit. Yet, LEED is building oriented and has never addressed the surrounding site conditions very well. As a result, a movement from within the landscape architecture community developed and released SITESv2 For Sustainable Land Design and Development in 2009 (Steiner, 2014).
|Table 2: SITESv2 For Sustainable Land Design and Development Categories|
|Soil and vegetation|
|Human health and well-being, construction, operations and maintenance, innovation and performance monitoring, and innovation and exemplary performance|
|Operations and maintenance|
|Innovation and performance monitoring|
|Innovation and exemplary performance|
SITES is a landscape performance rating system created in collaboration with the Lady Bird Johnson Wildflower Center, the America Society of Landscape Architects, and the U.S. Botanic Garden. It is a comprehensive rating system, similar to LEED, to improve sustainable site design, measure performance, and evaluate landscape value. SITES targets a wide audience including designers, contactors, operations, and landscape managers attempting to address more than just the design phase of land management (see figure 1). SITES rating system has eight categories (see table 2) including context and pre-design prerequisites. Yet, it does not have an explicit category for heat as an environmental hazard as it does for water. Cooling strategies to reducing the UHI is included in credit 4.9 within the soil and vegetation category. This deficiency is mostly likely due to our incomplete knowledge of human scale climate drivers. As of 2014, 160 pilot projects have gone through the SITES rating system (Steiner, 2014). LAF has supported the development of landscape performance metrics through its Case Study Investigation program, which links researchers, students, and practitioners to develop case studies of built projects. LAF has engaged 29 research teams, produced 76 case studies with 52 participating design firms as of early 2014. Partnering researchers, professionals, and students’ promises to create new knowledge for applied practice. This approach is particularly useful for urban climate issues due to our lack of knowledge about human scale cooling strategies.
Figure 4: Green roof laboratory research on the Design School Building at Arizona State University. Photograph source: Paul Coseo
Integrating performance for more sustainable urban systems
Incomplete human scale knowledge and the lack of usable metrics are coupled design problems. Researchers should follow three paths to address these coupled problems. First, continue laboratory-controlled studies on cooling strategies such as cool roofs, trees and vegetation, green roofs (see figure 4), and cool pavement. Second, continue to combine these laboratory experiments with model simulations to understand how site design changes may extend to larger urban scales. Third, expand partnerships with design professional and city officials to study in-situ site design and urban design cooling strategies. Only by working in partnership with designers and cities to integrate rigorous performance metrics into cooling strategies will researchers improve guidance for designing cooler infrastructure and move society forward toward more sustainable urban systems.
Dr. Paul Coseo is an Assistant Professor of Landscape Architecture and Senior Sustainability Scientist at the Global Institute of Sustainability. He is also a licensed landscape architect in the state of Illinois.
Header Image: Tempe, Arizona. Credit: Author