When you go on a road trip, you pack snacks and drinks and make sure you have good music to queue. Climate scientist Katia Lamer, on the other hand, packs party balloons loaded with atmospheric sensors, then climbs into a laser-firing observatory on wheels.
Lamer—director of operations at the Brookhaven National Laboratory’s Center for Multiscale Applied Sensing—recently completed a 1,700-mile road trip from Upton, New York, to Houston, Texas, in a specially designed science truck while taking a bevy of measurements, from air temperature to humidity to wind. The big plan: better understanding the complex climate dynamics of cities, where conditions can vary wildly not only from neighborhood to neighborhood, but door to door.
“The big difference with urban environments is that they're much more heterogeneous than natural environments. What that means is that there are more elements, like individual buildings, that create these canyons,” says Lamer, referring to the corridors between structures. “So if the surface is more complicated, that drives some changes in the meteorology at a much finer scale than we would have if you were looking at an ocean, which is uniform.”
Climate scientists have a good handle on how natural expanses of greenery like grasslands and forests affect their local conditions: When plants photosynthesize, they exhale both oxygen and water vapor, which cools the air—the vegetation is sweating, essentially. By contrast, the built environment of a city—concrete, glass, brick—is highly efficient at absorbing the sun’s energy, heating urban areas up to 20 degrees Fahrenheit above surrounding rural areas.
This is known as the urban heat island effect, a complicated phenomenon that Lamer is trying to measure with her observatory on wheels. The truck sports a lidar sensor, which fires lasers to track floating particles, thus measuring air flow. (Self-driving cars also use lidar to map their surroundings in 3D, but those lasers are bouncing off obstacles like other cars.)
This flow can vary significantly depending on the size and orientation of buildings in a given area. Two side-by-side structures of the same height, for instance, form a vortex that runs up the side of one and down the other. “What if you stack two buildings in a row, like if they're different heights from one another, how does that all influence the local weather? So that's kind of the frontier,” says Lamer. “In each neighborhood, each side of each building sees its own microclimate.”
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As the sun heats up one side of a building, it further complicates this movement of air, since hot air rises. But on the shaded side of the building, there might not be this same upward motion. Add winds to the mix and you’ve got atmospheric dynamics changing on very fine scales, both spatially and over time. “It's a very turbulent process, as the wind moves through this urban canopy,” says Vivek Shandas, who studies the urban heat island effect at Portland State University but wasn’t involved in this new research. “The science behind this really hasn't gotten a good grasp on the way the roughness moves the wind, and how it actually acts across an entire urban landscape.”
In addition to sensing with lidar, Lamer releases helium-filled party balloons that carry still more sensors, which beam atmospheric data back to the truck—so she gets measurements not only at ground level, but up to 3 miles above the city.
All this data will inform two main pursuits. The first is better understanding how cities actually influence the weather: As the sun heats up the land, the rising air might also carry moisture into the atmosphere, potentially influencing rainfall. Scientists understand how this works across bodies of water like an ocean, but not how the heat coming off an urban area like Houston might affect the weather above. More data will in turn give researchers a better way to represent cities in larger climate models. (Lamer hasn’t fully analyzed the data from the road trip, so she’s not ready to share results.)
Generally, though, as the atmosphere gets warmer, it’s able to hold more moisture, increasing the chances of extreme rain events and more flooding—which is yet another challenge for cities. “Transport of moisture is something that's really understudied in urban environments,” says Shandas. “As we start seeing greater levels of humidity, generally speaking—because of climate change, because there's just more moisture in the air—understanding moisture dynamics in urban environments will become a much bigger field.”
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The second scientific pursuit of the rolling observatory—and potentially others like it—will be to provide ultra-fine-resolution data on urban heat. “This kind of higher-resolution monitoring network can provide you neighborhood-level and street-level urban heat, rather than just a citywide average,” says Lei Zhao, a climate scientist at the University of Illinois at Urbana-Champaign, who studies urban climates but isn’t involved in this new work. “With a citywide average, you can hardly tell which neighborhoods are undergoing more climate threats, and it's hard for people to try to improve environmental justice.”
Previous research, for instance, has shown that poorer neighborhoods are consistently and significantly hotter than wealthier ones, exposing residents to more deadly heat. That’s because richer parts of town tend to have more green spaces, which cool the air, whereas low-income areas tend to have more heavy industry and big-box stores with huge parking lots, all of which absorb the sun’s energy. (More problematic still, poorer people have less access to air-conditioning.)
That said, there’s never any one part of town that is always cool or always hot, because temperatures can vary, even among blocks or buildings. “That's why urban heat is challenging,” says Zhao. “It's just so heterogeneous—neighborhoods-wise, buildings-wise, materials-wise, heights-wise. So it's not like forest or agriculture, which are more homogeneous.”
Luckily, scientists know full well how to mitigate the heat island effect: with green spaces. They not only cool the air but beautify neighborhoods and help soak up rainwater to avoid flooding. Researchers are also investigating how painting roofs white and deploying reflective roadways might further bring down temperatures.
At the moment, Lamer’s Brookhaven truck is the only one of its kind, wielding a unique array of instruments—although she thinks it would be useful to have a much bigger network of trackers. For example, she thinks sensors mounted on city buses might be a good way to take readings one day. Her next plan is to build another mobile observatory to cover more ground, with the idea of sending both vehicles to drive around New York City. Together, they could gather enough data to inform where to put permanent weather stations for long-term climate monitoring.
With more journeys around cities, Lamer can build better maps of how heat differs across urban areas, and how the heat island effect might influence the weather, and what that means for regional climates. “Which neighborhoods have more vulnerable populations that need more support?” Lamer asks. “I think that's why urban research is picking up some steam, because there's a need now to intervene to create mitigation strategies in cities.”