Computing Applications

Mitigating Urban Climate Change


Planting trees—lots of them—is one of the most popular ways local governments attempt to counter the warming effects of climate change. Worldwide, municipalities have launched tree planting programs with great fanfare: in 2007, for example, Boston announced its “Grow Boston Greener” effort, with a goal to plant 100,000 trees.

By 2020, however, that effort had not yielded much; in fact, according to researchers from Boston University, urban tree canopy in the city may actually have decreased since that now-defunct program launched. It was, they said, emblematic of a well-intentioned but poorly implemented attempt to do something assumed to be beneficial to combat climate change, but without a master plan in place to make it successful.

Tools, money, and perspective

If “Grow Boston Greener” was a lesson in failure, the city has learned from it. In their paper mentioning the program’s failure, the BU researchers noted they had formed a partnership with the city in 2018 to address issues affecting urban tree planting projects. In 2020, they introduced a digital decision support tool called Right Place, Right Tree Boston. The tool, which the authors said could be customized and used nearly anywhere in the U.S., was just one piece of a new, more disciplined, collaborative approach.

By 2023, the city had implemented its Urban Forest Plan, aided by $11 million in funds from a U.S Forest Service grant. And Boston is not alone in receiving significant new federal funding. In late 2022, the U.S. Department of Energy awarded $85 million to four Urban Integrated Field Laboratories (UIFL), charged with developing what the DOE called “comprehensive projects, including field observations, data assimilation, modeling, and model-data fusion, to inform equitable solutions based on state-of-the-art uncertainty quantification and data analytics.”

“Equitable” is key to understanding the new climate mitigation projects. The uneven results of earlier haphazard “plant some trees” approaches have been amended to include comprehensive planning with those in the communities most affected by climate change, not as passive receivers of scientific information but as active and equal collaborators.

Benjamin Zaitchik, professor of earth and planetary sciences at Johns Hopkins University in Baltimore, is the lead principal investigator of the Baltimore UIFL; he says the program marked a departure from the usual DOE grant process.

Zaitchik said two of the pillars of the grant application involved traditional scientific parameters around the physics and chemistry of urban climate, but the third pillar, supporting equitable solutions to climate change, was a new parameter. “That was new for the DOE office of science,” Zaitchik said. “They’re a pure science office and they are still a little ginger around that topic, because they need to keep their hands out of policy.

“The way we wrote the grant was, we led with that last pillar, to co-generate knowledge from the beginning. Then you build the system around that; you don’t tack that on at the end as goal #3 of a project you are just designing for science. I was flabbergasted when we got funded.”

The prism of perception

Perhaps Zaitchik’s sense of surprise was unfounded. Along with other climate research experts in the U.S., he recognizes the demands of trying to accurately model urban climate data, and then to craft some sort of consensus beneficial policy around that data, is a prism of many disciplines rolled into one overarching endeavor.

For instance, when asked to consider whether the primary question around the new emphasis in urban climate research, and the funding for it, should be focused on physics, economics, public health, or sociology, every expert who spoke with Communications had a different angle.

Rao Kotamarthi, senior scientist in the environmental science division of Argonne National Laboratory in Chicago and deputy director of the UIFL there said dealing with urban climate change is primarily economic, followed by public health considerations. Vivek Shandas, founder of the Sustaining Urban Places research lab at Portland State University in Oregon, said the problem at its core is one of public health. For David Nowak, emeritus senior scientist at the U.S. Forest Service, who wrote or co-wrote many of the foundational studies in the field, having the physical data comes first.

Zaitchik’s first response to all this was, “Yes, it’s clearly all those things,” followed by an explanation in detail that looking at deceptively intricate questions, like the best ways to mitigate “urban heat islands,” which has to consider interconnected factors like human exposure to excessive heat at the scale of an individual street and the effects of mixing air from outdoor and indoor environments. Then, he said, to try to fully understand which mitigation attempts might work best, they must utilize public health records, which are often aggregated at ZIP code (U.S. mailing zone) levels, far too large for planning at a neighborhood level.

The widespread adoption of electronic medical records has helped make aggregated granular health data more accessible, he said, though that is still data gleaned from individual encounters with a local health system, which he said poses more questions.

“How many people might seek an encounter, as opposed to those who don’t? And how do we account for chronic versus acute exposures, for instance? The epidemiology there is tricky, but we are at the point we can ask those questions. Then you go have to back to the physics: ‘okay, now that we have tagged these records at x scale, do we have confidence in the exposure estimates at that scale? Are they inside or outside exposures?’ And that just deals with the public health and physical climate data. There are a couple of other fields you need to consider when it comes to intervention strategies, and that’s where the sociology becomes central.”

The Chicago UIFL, formally known as Community Research on Climate and Urban Science (CROCUS), is working with three community organizations to lay the foundation for its work over the five-year grant period. Kotamarthi said those organizations are considered full partners from the start.

“You don’t want them to feel that this is an extractive process, that you are extracting data from the community and what they get is a publication in a journal. That’s the first mistake you can do, and we are trying not to do that. From the very beginning of the project, they are actually co-investigators in the project, and the science questions we developed were actually developed in consultation with them.”

New data possibilities

To begin to answer the multi-layered questions, improving urban ecology presents requires the use of a lot of data on which the scientists and community partners can act. That data ecosystem is just now beginning to coalesce, not just from the measurement side, but from a basic inventory of what already exists. The Forest Service’s Nowak said that municipalities have long kept inventory of their physical assets, and that sort of attitude is only now beginning to emerge in urban ecology, as evidenced by Boston’s comprehensive citywide tree inventory made available in its plan.

“There were a lot of papers in the 1980s and 1990s talking about benefits of trees, but they never measured anything,” Nowak said. “We knew how many light poles we had and how many cars were registered, so getting that physical data leads to understanding both the number of trees and leaf area and cover they have.”

Portland State’s Shandas said greater official recognition of the importance of accurate data is coincident with the proliferation of new sensor technologies that allow anyone to become a citizen scientist.

“Most urban environments have a handful of pretty systematic and scientifically reliable observations. They often come in the form of federal and state meteorological stations; that’s what has been used for decades to do this work. In the past decade, companies like Weather Underground have emerged and tried to create a sort of community citizen science approach to creating a greater number of observation networks.”

The availability of these new sensor networks enables the academic researchers to build what Shandas called “civic legitimacy” in designing studies that call for community members to participate in the research themselves.

“They are out there collecting the data,” he said. “They are able to understand the process. They co- design where the sensors go, how they’re deployed, what the measurements are, what they mean, and so on. So that scientific rigor piece, with the funding the DOE has put forward, has taken on a whole new caliber of complexity, of resolution, of understanding dynamics generally. That’s phenomenal, though I think it will still be many years out before we start getting a real understanding of what is happening in these very complex, heterogeneous environments.”

Kotamarthi said CROCUS researchers have made it a priority to find a way to train machine learning models and create intuitive “clear” user interfaces on top of the physics-based models they are now creating. That way, the community partners can show local officials what needs to be done, with the data to back up their needs. One of the group’s earliest works, published in February 2023, explored the comparative benefits of white painted “cool roofs,” “green roofs” that contain a light layer of vegetation, and solar-paneled roofs that reduce demand on public utilities in mitigating heat waves —while demonstrating the complexities that need to be modeled to deliver usable solutions.

Johns Hopkins’s Zaitchik said the Baltimore UIFL researchers are still feeling out which sorts of data tools they should be developing.

“There are a lot of different entry points,” he said. “I’ll admit I have a little bit of app fatigue or skepticism at this point. One thing we’re really focused on right now is that element of authority. They don’t have to become Ph.D. data scientists; they need to know a few things about this. They need to be invested. They need to feel like they can work with people on solutions.”

Zaitchik said he has noticed that when he and a community representative address an audience together, that audience still tends to defer to him as the expert, the authority, and that is something he would like to see changed.

“Actually, he has the wisdom; how do we get to the point where he can provide the authority through which other people can feel the authority themselves? And you don’t do that with an app. You do that with people.”

Gregory Goth is an Oakville, CT-based writer who specializes in science and technology.

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