“We are able to quantify how different the results would have been in real events,” says de Guzman. “I know that higher numbers of extreme heat days are predicted in each of these communities.”
In other words, the time to act is now. On the one hand, tall trees provide shade, but plants generally release water vapor during photosynthesis, i.e. “sweat”. Accordingly, a high-income neighborhood with lots of parks and landscaped areas might be 15 degrees Fahrenheit cooler than a lower-income, more industrialized area—like so many health threats, heat disproportionately affects those who are most disadvantaged. The urban heat island effect varies not only from neighborhood to neighborhood, but also from block to block and even from house to house. Different building materials, such as wood and brick, absorb and store solar energy in different ways.
The benefit of this type of research is to first find entire districts that are a priority for greening and then to specifically select specific locations to plant individual trees. “We don’t necessarily plant entire forests in urban areas — we plant a single 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 limited resources and know where deploying this measure will have the greatest impact, being able to identify those locations is a no-brainer.”
But it’s not as easy as just sticking a bunch of trees in the ground and calling it a day. LA has embarked on a multi-year urban forest management plan to increase tree canopy, particularly in the most vulnerable neighborhoods. It must carefully identify locations to grow the plants, but also work with local residents – for example at community feedback meetings. Some people may not want trees in front of their house: perhaps a branch once fell on their car or their sidewalk cracked due to roots underneath, limiting the mobility of a grandparent in a wheelchair.
So creating more trees in the urban landscape is also about collaboration and education to make people aware of the significant benefits of cooling that could save their lives – and at least reduce their air conditioning costs. “If there is a negative tree story, we need to educate about how we can do better in the future,” said Rachel Malarich, the Los Angeles city forester. “As an industry, we have learned to be more selective about what we put where and to adapt it to the location or change the location so we can plant something larger.” For example, if a particular piece of soil is too small to support a species of tree To provide space large enough to provide good shade, perhaps the city could redesign sidewalks to accommodate that space while improving mobility And Reduction of local temperatures.
In LA and elsewhere, scientists are racing to find tree species that can withstand temperatures 10, 15, 20 years from now – you don’t want to plant a tree only to find that it can’t survive in the new climate. Climate change may also contribute to the spread of tree pests and diseases, making urban greenery even more precarious: A particular community may be interested in planting more of its neighborhood’s signature tree species—magnolias or whatever—but the future might become increasingly hostile towards it.