“We can quantify how the results would have been different in real events,” says de Guzmán. “I know that projections indicate an increased number of extreme heat days in each of these communities.”
In other words: now is the time to act. Tall trees provide shade, for example, but plants generally release water vapor as they photosynthesize, essentially “sweating.” Consequently, a high-income neighborhood with many parks and gardens could be 15 degrees Fahrenheit colder than a more industrialized, low-income area; Like so many health threats, heat disproportionately affects the most disadvantaged. The urban heat island effect varies not only from one neighborhood to another, but also from one block to another and even from one house to another. Different building materials, such as wood and brick, absorb and retain the sun’s energy in different ways.
So the usefulness of this type of research is to first find entire neighborhoods to prioritize greening, but then focus on specific locations to plant individual trees. “In urban areas we don’t necessarily plant entire forests; we plant one individual tree at a time,” says Vivek Shandas, a climate adaptation scientist at Portland State University, who studies the heat island effect but was not involved in the new research. “If you have a limited amount of funding and you know where there will be the biggest impact from rolling this out, it’s a no-brainer to be able to identify those locations.”
But it’s not as easy as just sticking a bunch of trees in the ground and calling it a day. Los Angeles has embarked on a multi-year campaign Urban Forest Management Plan to increase its tree cover, especially in its most vulnerable neighborhoods. You have to carefully identify places to add the plants, but also collaborate with the residents there, for example, with community feedback meetings. Some people may not want trees outside their house: Maybe a branch once fell on their car, or their sidewalk cracked from underlying roots, reducing the mobility of a wheelchair-bound grandparent.
Therefore, getting more trees in the urban landscape also involves collaboration and education, getting people to understand the important benefits of cooling that could very well save their lives, and, at the very least, reducing their air conditioning bills. “If you have a negative story about a tree, we have to do some education about how we’re going to do better in the future,” says Rachel Malarich, forestry officer for the city of Los Angeles. “What we’ve learned as an industry is to be more selective about what we put where, and make it appropriate for the site, or change the site so we can plant something bigger.” For example, if a given patch of land is too small to accommodate a species of tree large enough to provide good shade, perhaps the city could reshape the sidewalks to accommodate that, while improving mobility. and reducing local temperatures.
In Los Angeles and elsewhere, scientists they rush to find tree species that will be able to withstand temperatures within 10, 15, 20 years; You wouldn’t want to plant a tree and discover that it can’t survive in the new climate. Climate change can also contribute to the spread of tree pests and diseases, adding even more precariousness to urban greenery: a given community might be interested in planting more tree species characteristic of its neighborhood (magnolias or whatever), but the future may be increasingly hostile to him.
