A new map of Los Angeles highlights one form of inequality: which of the city’s streets and homes get the benefit of shade from the the city’s 10-million-plus trees. The city is the first to pilot a new tool from Google, called Tree Canopy Lab, that was used to create the map.
L.A. plans to plant 90,000 trees by next year as part of its version of the Green New Deal, and to increase the tree canopy in the areas that need it most by 50%. It’s targeting neighborhoods “most impacted by extreme heat related to climate change,” says Rachel Malarich, the city’s first-ever forestry officer. While trees have multiple benefits in cities, from improving air quality to boosting mental health, they’re also particularly helpful in mitigating the urban heat island effect—the fact that large swaths of concrete make some neighborhoods even hotter when temperatures rise. The EPA reports that shaded surfaces can be 20 to 45 degrees cooler. The new tool can help identify the areas to prioritize for tree planting.
Google launched the project as part of Environmental Insights Explorer, a platform it created to help cities deal with climate change and air pollution. It started by partnering with L.A. to understand the city’s needs, then designing a solution that it plans to make available to other cities. “One of the best ways for us to do hundreds or thousands of cities is to first do one or two cities,” says Nithya Sowrirajan, a director at Google Maps.
Los Angeles is also counting trees the traditional way, with workers going block by block and laboriously noting the species, size, and condition of every tree growing on the street. That’s something that’s needed for the city’s forestry department to manage public trees. But the process is slow, and it misses the vast majority of trees in Los Angeles: 90% are on private property. To understand the full picture of which areas most need more trees now, the city needs a broader view. In the past, it has relied on another complex process that involves a plane using LIDAR laser technology and a team performing analysis—complicated and expensive enough that it rarely happens, and slow enough that it’s outdated by the time it publishes.
Previously, the city didn’t “have that ability, especially in this decade of climate action to really be able to check how we are doing and have regular updates without having it be an expensive process,” says Malarich. “Google’s made it so we have this platform not only to explore and think about better decision-making right now, but also not have me already strategizing how I’m going to get a similar canopy assessment in a couple years to track our progress. That would cost resources now in terms of my time, as well as future funding that we would have had to track down to do those kind of analyses.”
Google uses AI to quickly analyze aerial photos of trees. “The tree detection algorithm analyzes it from different angles and calculates the average tree canopy,” says Sowrirajan. The company also helped develop a similar tool, called Global Forest Watch, that can track deforestation in remote areas by analyzing satellite data. In cities, the tree analysis can be combined with other key metrics. “We have public datasets where we bring in heat indexes,” she says. “We’ve brought in population densities. And overlaying those is sort of like your magic calculation of where the populations are the most vulnerable due to low tree canopy cover.”
More than half of the people living in L.A. live in areas with less than 10% tree canopy coverage. Research suggests that the canopy cover has to reach 40% to significantly lower temperatures. Forty-four percent of Angelenos also live in neighborhoods with extreme heat risk. There’s a clear connection between the areas that lack trees and those that see the worst heat.
The new tool will help the city identify the best places to plant, starting at the broad level—which areas have the fewest trees and the highest risk. Then the team can identify more specific places to plant. “We’re able to scale down into that neighborhood and say, Okay, what are the land use types here?” says Malarich. In an area with apartment buildings, there might not be as much room for trees in front or back yards. That might mean bigger changes: In some cases, a street might have to be redesigned to “provide more large-stature trees to provide those health benefits and protections to the public,” she says.
Google plans to work with the city to continue developing Tree Canopy Lab, and will soon make it available to other cities. “The urban forest community is fairly small, and there are several others that are trying to be pretty aggressive with their canopy equity targets,” Malarich says. “And the feedback that they’ll provide will only make this tool stronger.”