Why heat? Why cooling now?

Working with the City of Tempe to better address resilience to extreme heat, two key questions arose: Why heat? Why now? It’s always been hot in Arizona, why should the City pursue cooling and why now? These are two questions that developers, owners, planners, designers, builders, and maintenance businesses should be asking why heat and why cooling now – what is our role in building and nurturing a cooler urban Arizona (e.g. Phoenix, Tucson, Flagstaff/Sedona, Yuma, and other smaller urban areas)?

Why heat? Heat is a silent killer. Yet, heat also degrades quality of life and our investments in the places we build by limiting the times of day government and businesses can safely invite walkers, shoppers, and event goers to partake in our amazing Arizona public and private social spaces – heat stifles our outdoor Arizona social life and culture. More heat diminishes our ability to pass on our rich outdoor heritage. The heat is also getting worse (figure 1). By the 2060s, the summer of 2020 might be a normal summer. Some of that heat is inevitable (i.e. lack of local control over global aspects of climate change) and some of it frankly is unnecessary (i.e. more local control over urban heat island). In part, the way we have designed too many car-oriented places over the years has greatly contributed to hot spots with wide roads, parking lots, limited shade, lack of vegetation, poor quality sidewalks, and minimally designed places for pedestrians. Although climate change is making heat waves worse, we’ve designed too much of urban Arizona to be hotter than it has to be and community leaders, economic development officials, and researchers are moving toward addressing this unnecessary heat. Some of the urgency comes from the fact that many times those hotter spots burden our most vulnerable neighbors, workers, and customers who work outside, take public transit, or don’t have good quality air conditioning. The urgency around heat is a social justice, economic prosperity, health, and livability answer. We have a good enough understanding of urban greening, urban materials, and urban form strategies (see May and June ULI newsletter) that can make hot spots cooler, thus making the our cities more just, economically competitive, healthier, and more livable for our children and grandchildren is well within our collective power.

Figure 1: A National Weather Service, Phoenix graphic showing observed 110°F days with a record number in 2020 of 53 days, which shattered the previous record of 33 days. Climate models suggest 2020 will be a normal summer by the mid to late 2000s.

Why cooling now? Urban Arizona is experiencing one of the biggest demographic and real estate development booms in the country. The Phoenix-Mesa-Scottsdale metro area saw a +9.7% increase in population since 2015 as opposed to only a +2.7% increase in the US as a whole. Now is the time to channel that associated urban development growth to tackle unnecessary heat related to poor design. If we know that 20^th Century design ideas led to hot spots, why would we continue down that path? We know better not to repeat past mistakes with poor pedestrian environments. A 2019 (p. 19) Urban Land Institute “Scorched” report describes the urgency for the design and real estate development community (e.g. investors, developers, owners, and regulators along with practitioners from planning, design, engineering, and construction) “[a]s temperatures rise, developments that plan for extreme heat may gain a competitive advantage, whereas developments that are not prepared may incur costs…”. The report describes the urgency of heat for urban developments including the risk for:

• negatively impacting revenue for outdoor-dependent retail, recreation and travel industries as consumer preferences change;
• hastening deterioration of building and landscape materials with higher maintenance and operations costs;
• increasing energy use with associated costs;
• more frequent business disruptions from power and water failures (e.g. as in Texas in winter 2021 extreme cold), transit interruptions, and wildfires (and smoke);
• developer and owner liability “…for system failures, degraded building materials, unstable operations, suffering tenants, and secondary impacts caused by buildings (such as melting parked car mirrors from reflected heat…)”(Scorched, 2019: p. 21); and
• new regulations that could require new and/or existing buildings be compliant with heat reduction strategies.
  

Why cooling now, also aligns well with other 21^st Century sustainable development agendas such as transit and pedestrian oriented developments, 20-minute city concepts, and biophilic city design. Why cooling now, is that its already happening to some extent in parts of the State, but could be better coordinated create co-produced cooling guidance and policies for urban development including rules that reward cooling. Why cooling now, is that time is running out to channel the current growth toward a cooler future that everyone wants. Once an area develops, it locks that built environment into that urban configuration for decades. We have to ask ourselves – why should we create more hot places if we know better? “Investing in heat-mitigation technology and approaches can lead to a host of benefits, such as

• improved tenant experience,
• reduced operating costs,
• improved likelihood of business continuity,
• enhanced branding, and
• additional foot traffic in pedestrian and retail environments.” (Scorched, 2029; p. 17)

Innovation in Urban Greening for Cooling Desert Cities

Luckily, the design, development, and research community have developed a host of resources to advance more effective cooling through urban greening, urban materials, and urban form strategies. Here, we focus on five key innovations that contribute to more effective urban greening for cooling desert cities along with arguments for compact development (population and housing density) that can water those thirsty green spaces.

Recommitments to quality urban pedestrian environments (that include cooling) – Increasingly, cities, developers, and owners are recommitting to high quality walkable environments that include cooling considerations from the initial conceptual design phases through to construction. ULI’s Developing Urban Resilience case studies highlights the City of Phoenix Housing Department’s Edison Eastlake redevelopment in partnership with Gorman & Company, Mithun Inc., and Arizona State University. This collaboration brought together industry, research, and best practices for a community participatory approach to design a compact and thus cooler neighborhood. On the community side, neighbors contributed their existing heat experience and expertise with navigating a hot neighborhood, which was integrated into where cooling strategies were needed most to improve pedestrian cooling. Importantly, urban greening discussions of cooling were not divorced from other urban design conversations to discuss trade-offs between strategies (e.g. if tree planting was not possible due to utility conflicts, then what were other socially acceptable cooling solutions such as shade structures and water features). It also facilitated community learning about why some urban spaces are hard places to plant trees that may not be visible apparent or obvious to residents. Housing officials, planners, designers, engineers, and developers integrated the contextual community information along with heat research on district cooling, which also resulted in a useful Heat Action Planning Guide to share the process. This guide includes design principles for shade (and cooling, p. 99). In this example a foundational cooling strategy was the compactness of the neighborhood with building shade being the underpinning upon which urban greening was added. The radical notion in this partnership is that they combined the greening, compactness, and cooling knowledge, will, and control over that cooling to create a comfortable and walkable neighborhood – this may be a model for what can be done when we put all the best heat, urban greening, urban design, and walkability practices together.

Rethinking our water use and tree shade as per capita – With compactness as the cooling foundation, condensing housing, retail, and office allows for greater reallocation of water usage to support enhanced urban greening that benefits more business owners, workers, and residents. A 2017 study reports that “Scottsdale, one of the wealthiest cities in the state, has large-lot residential estates and a per capita annual water use of about 302 m3 in 2009… In compact communities with housing density of 37-74 units per hectare, per capita annual water use can be as low as 75 m³ per person (Gober & Kirkwood, 2010).” (Yang & Wang, 2017: p. 12). That’s a benefit that compact development can reduce water use per capita by up to four times that water use in lower density communities, which frees up at least some water to support urban greening for pedestrians. In addition, denser populated areas can use more water because the same vegetation will benefit more people. A street tree on Central Avenue in downtown Phoenix could provide shade for hundreds of pedestrian commuters per week, whereas a similar street tree in a gated community may only be serving a limited of number of pedestrians. Theoretically the same water use, but substantially different impact because of the population and housing density. These areas also may have more water if we look at all the potential water sources through compact urban neighborhoods.

Reimagine underutilized water sources – Water harvesting and grey water reuse are not new strategies in Arizona. Regionally, Tucson has innovated many policies and design approaches to making better use of our water resources. Yet, in many other urban Arizona cities, our current approach to water leaves so many water sources untapped — it should be considered wasted water. Every day we bring water into our homes, businesses, and other buildings. At least for some of the least dirty water, why would we then pay to send it back to use more energy and resources when it could give us more benefit for supporting trees and vegetation for free! ECO PHX is one recent multifamily development, under construction, that is going to integrate grey water reuse into landscape areas to sustain larger trees and a cooler pedestrian streetscape in the Roosevelt Neighborhood of Phoenix. Another promising avenue for growing water is from the sky. Teams of researchers and practitioners have been working for years to provide tools kits, guides and handbooks to use stormwater more effectively to support urban vegetation. It’s free and though it doesn’t fall often, even small rainstorms can provide lots of water because of all our roof and pavement surfaces in compact neighborhoods that could be used for collecting rainfall.

Recast our desert natives into new roles in our designs – In many cases, we might have compact, walkable neighborhoods, but we plant them with an abundance of non-native plants. Our Sonoran plants have had thousands of years of preparation for the job of thriving in the arid heat. Luckily, we have diverse Arizona ecosystems from pine forests to desertscrub. Even in our hottest desert ecosystems, desert tree, shrub, cacti, and groundcover communities are found on alluvial plains intermittently broken by perennial washes and wetter rivers and wetlands. The biodiversity provides us with a rich place-based pallet to populate our diverse urban places (e.g. from very dry yards to flood irrigated parks). It’s not to say that non-native desert adapted and xeric species don’t have a role to play in our urban landscapes, but the natives deserve a larger stake in the microclimate moderation game. Biodiversity is a key component to increase resilience to the heat, pests, and other hazards that threaten our urban vegetation. Keeping our urban greening strategies biodiverse is critical. Anecdotal stories about trees dying from summer 2020 extreme heat may provide an early warning on certain tree species being unable to withstand future heatwaves. Besides, what is urban Arizona without it’s native plants – Los Angeles, Houston, Dubai? The foundational character of a place is its native plant and wildlife communities combined with its climate, water and geological inheritance that can’t be found elsewhere. The Central Arizona Conservation Alliance (CAZCA) has four goals for it’s Regional Open Space Strategy for Maricopa County: 1) Protect & Connect; 2) Sustain & Restore; 3) Love & Support; and 4) Coordinate & Elevate. In particular, the Sustain & Restore goal “…includes a variety of initiatives, including research about the impact of using desert parks, research about effective invasive species control and removal and working to return native plants to the landscape.” Including more natives can contribute to this goal, reduce water use, contribute to the sense of place, and moderate hot environments with plant species representing our lowest deserts to our highest pine forests to our rich riparian forest communities. There are many resources to advance knowledge about urban vegetation including Phoenix Metro Urban Forestry Roundtable, CAZCA GreenPrint webtool, Trees Matter tree database, and the Maricopa County Department of Air Quality tree list that includes trees that contribute to poor air quality through biogenic volatile organic compounds (BVOC).

Renew a spirit of innovation to export to other cities facing similar heat challenges – Finally, our design, development, and research community is already innovating on the frontlines of having to design with heat out of necessity, but there is room for innovation in planning, design, policy, practice, and operations. The ULI case study of Kierland Commons in Scottdale might show us the way toward cooler Arizona places, where the “…streetscape is designed to maximize comfort in the harsh desert heat. The walkways between retailers use five different canopy designs—featuring trellises, wood and mesh awnings, and misting systems—to shade and keep shoppers comfortable even during the hottest Arizona days. Retailers were initially concerned that the canopies would block the visibility of their stores; however, the shading devices have become an integral and defining feature of the retail areas. Restaurants offer covered outdoor seating and floor-to-ceiling windows that open onto the street, allowing patrons simultaneously to enjoy the air-conditioned indoors and the fresh air while remaining part of the streetscape.” (p. 62-63).

Our community can and should be leaders of designing and developing cool urban people places so that we can leverage that expertise and export our knowledge of how to cool cities to other regions. Not only do we have more days a year when we can see our designs “working” (i.e. providing cooling) because of our plentiful sunshine and hot weather, but we also have the urban laboratory (i.e. urban growth), the skill, and the vision to make it happen. Most cities experience some form of heatwaves and they are becoming more intense, frequent, and of longer duration. The world needs our cool urban design innovation that combines urban greening and density. In many cases, we are already doing the work – how will we work together to deliver our innovation to the awaiting world?