'All shade is good shade:' The roles and challenges of trying to mitigate Phoenix heat with shade

Less than a year ago, the Phoenix City Council unanimously approved a plan to increase the amount of shade across the city.

"Shade Phoenix” calls for 27,000 new trees and 550 new shade structures over the next five years — more than half of the more than $60 million total investment is to be made in low- to moderate-income communities.

Dave Hondula, director of Phoenix’s Office of Heat Response and Mitigation and faculty member at Arizona State University, joined The Show to discuss how big of a role shade plays in overall heat mitigation.

Full conversation

DAVE HONDULA: Well, Mark, I'm so grateful to be having this conversation. The fact that we're even having a dialogue focused on shade is very consistent with the vision and language that the city has rolled out in our new Shade Phoenix plan and also consistent with what we're hearing in the research community now about, just how important shade is. It could be argued that shade is the single most important strategy for keeping people cool in hot environments, and that's especially true in a desert climate like ours.

MARK BRODIE: How do you determine what kind of shade is most appropriate in a particular place?

HONDULA: Oh ... that's a complicated question, and a lot of people have different opinions about it. Yeah, cities are really challenging environments for construction of all kinds and that ... is also related to shade. And, of course, we want to orient ourselves thinking that that shade can be provided from natural sources like trees. From intentionally built structures like shade sails, shade canopies, ramadas. But also, buildings themselves cast a lot of shade and shadows in the environment that count as well as, as part of the whole story.

As our team and the city team is looking to implement shade, I think we're trying to strike a balance between natural and engineered, or built shade. Although I don't have a magic ratio for you. I think some specific sites present opportunities a little more clearly for some types of shade than others. For example, we're thinking about pedestrians in the right of way who might be forced to wait at an intersection. An intersection presents so many complexities in terms of what's above ground, below ground, what visibility needs to look like. That it might be more feasible to engineer our way into a structure there rather than plant a tree, which might not have access to the resources it needs below ground. It might be really difficult to have a healthy tree in that environment.

So, we really do try to treat it on a case-by-case basis. But, certainly trying to strike a balance, because we know natural and engineered are both important and valued by the community.

BRODIE: Are there differences in the type of shade provided by, you know, for example, trees versus buildings versus like shade cloth? Like, is some shade better than others in a sense?

HONDULA: Some shade is better than others, and I'm so glad you asked and have the chance to point to some of the work of our ASU teammates. ASU, and some of our other colleagues around the country, have been really closely looking at this, and it turns out that there is a pretty measurable impact, in terms of what the body heat load is, what the body's heat stress might be under different types of shade. And ... we can imagine, even just as I'm looking out the window right here at City Hall, you know, a very consistent uniform shade, a shadow provided by a building, versus maybe more of an intermittent shade or, or thinner shade — I sometimes describe it — by some of our desert trees. Particularly if they're more isolated. So yes, we do need to be mindful of that, although I think an important message is that all shade is good shade. All shade makes a really, really big difference, in particular compared to other types of cooling strategies.

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BRODIE: Sure. I'm curious about the challenges that trees and specifically planting trees provide in terms of ... finding trees that will be OK to survive here. And also, trees obviously take time to grow. So, you know, if you plant a sapling, it's not going to provide shade really for quite a while until it grows to some height. So how do you try to go about finding trees that will be big enough to do the job you're hoping that they do — and also sort of be desert adapted enough, not use too much water and provide, you know, the kind of shade that will really be beneficial?

HONDULA: Yeah, I think you're absolutely right that we're, we're trying to find that sweet spot, for tree species selection that balance these many different interests and sometimes competing interests. Water use, shade quality, thorns, food, allergens, air quality considerations. There are many factors that come into play here. Fortunately, there's been a great collaboration in our region, working on that through the Metro Phoenix Urban Forestry Roundtable. Experts from all across the Valley, as well as some national partners coming together to have that dialogue, put together a guidance that we can use as a city and our partners can use to inform our programming. For example, participants in our neighborhood grant program right now have access to a list of our recommended species and will only choose trees on that list that we think do a good job of balancing the many different considerations. But, it's a work in progress, and it will always be a work in progress because the nursery industry itself is constantly innovating.

BRODIE: How is the city doing in terms of meeting the goals of — I know, around 27,000 new trees planted, 500 some-odd new shade structures in the next several years here. How is the city doing?

HONDULA: My sense is that, in this first year of the shade plan era, our City Council unanimously passed the new Shade Phoenix plan last November and we'll be reporting on the first year of that plan, here later this year. But, my sense is that we're on track, if not ahead of track. But we're looking forward to delivering a full accounting of progress across all the actions in the shade plan to the public later this year. And that's a really important step that we need to take, is having a more consistent dialogue with the community on how we're doing.

I think we've heard concerns from the community in the past, that maybe that conversation has not been as complete, as transparent, as robust as it could be, as the community is seeking. And we're really eager to deliver on a commitment for more consistent and complete reporting in the shade plan era.

BRODIE: What are you hearing from private property owners, businesses, homeowners about their efforts or their desire to add shade? Maybe challenges they've had in terms of trying to do it?

HONDULA: Yeah, certainly an appetite to do more and to get involved, and we are in constant dialogue, with homeowners, with renters, with businesses about what those challenges are and what their vision is.

I'm thinking specifically about a comment, I'll go back a few years, it's some work that the Nature Conservancy was leading, trying to understand these really local issues and concerns. And in some of the neighborhoods where the Nature Conservancy was working, a constant message we heard was, “We'd really like to participate in some of these tree giveaway programs, tree grant programs, but I've got a dead tree in my yard right now that's right in the spot where I'd like to plant a new tree and it's really costly to remove that dead tree.” That was a barrier in the system that was discouraging and preventing people from participating.

So, as we had the chance to design new programs with the resources that our City Council allocated or the federal government allocated, we're trying to take a much more expansive approach to, “What does it mean to have a tree planting project? Yes, let's invest in some of those other landscape modifications, tree removal, whatever it might be, that can help us get to the next step.” And I think we need to constantly have our ears open to what those types of concerns are. If we're, if we're not addressing all those individual concerns, I'm nervous that we'd be missing a lot of the opportunities that are out there.