The hottest day recorded in San Francisco was on Sept. 1, 2017 when the temperature rose to a sizzling 106 degrees. Last week, Livermore experienced that same insane spike of heat that San Francisco once experienced, topping off at 106 degrees on June 17 and June 18, and Sacramento hit a new heat record of 109 degrees. In other inland areas like Santa Rosa, Concord and San Jose, too, the heat was so scorching that the asphalt shimmered, trees drooped and walking dogs had their tongues out.
In the last year we’ve been through fires and pestilence and now we’re back to worrying about a hot, dry spell with the specter of the epidemic not quite in our rear view.
While there is a balmy breeze blowing and pleasant blue skies as I write this, it could be short-lived. Another heat wave is likely to descend on us, centering on Northern California by next weekend, say weather forecasters. How will San Francisco hold up in the next heat wave, or the ones after?
Let’s start with the question of why we get these heat waves?
It really comes down to global warming, said Daniel Swain, climate scientist at the University of California, Los Angeles Institute of the Environment and Sustainability. The climate is several degrees warmer than a few decades ago; this increase in heat on the earth’s surface results in a faster rate of evaporation of water from rivers, streams and soil.
And “as soil moisture decreases, there’s less water to evaporate, so an increasing fraction of solar energy is going toward heating the atmosphere and heating the ground,” Swain explained.
When water evaporates rapidly, there is less water available for humans, animals and the landscape, leading to drought. We need water to fall from the sky as rain and snow, but while rainfall does mitigate, it doesn’t solve the problem of heat and drought. According to Swain, long term trends in California do not show a decrease in precipitation, “but you do see an increase in the severity of drought.”
This then becomes a cycle. Increased severity of heat leads to dry conditions and drought, which generates more heat and more drought.
This is particularly bad news for low income neighborhoods and communities of color. In 2013, one study by University of California, Berkeley professor Rachel Morello-Frosch found that minorities are most at risk during heat waves, suffering the effects of climate change disproportionately.
In a 2019 study of 108 urban areas, formerly redlined (predominantly non-white) neighborhoods were hotter than non-redlined neighborhoods “by as much as 7 degrees C.” One reason for this is that there are more trees in affluent areas, providing shade for the wealthy. In contrast, poorer neighborhoods tend to be exposed to hard, hot asphalt and concrete spaces.
Indeed, a quick survey of San Francisco’s tree coverage patterns supports the study’s results, to some extent. According to data from San Francisco’s Climate and Health program, Chinatown has 5 percent tree cover compared to 32.8 percent in Presidio; Bayview/Hunter’s Point has 6.7 percent to Seacliff’s 29.3 percent; and Excelsior has 10.3 percent shade to Noe Valley’s 15.5 percent.
Not surprisingly, the populations in Chinatown, Bayview/Hunter’s Point and Excelsior are 87.9, 79.7, 66.7 percent non-white, respectively. And the economic resiliency score (reflecting the number of people over the age of 16 who are employed) of these neighborhoods is between 1 and 2 (with 1 being the least resilient) compared to a solid 5 (most resilient) in Presidio, Seacliff and Noe Valley.
Trees are an important and effective part of the arsenal against global warming and heat waves. Street Tree SF has been engaged in pruning and maintaining trees and removing dead trees since July 2017. That’s needed work. But what about planting new trees?
In interviews, Carla Short, superintendent of the Bureau of Urban Forestry at San Francisco Public Works, has stated the desire to plant 6,000 trees every year, especially in disadvantaged areas that have low tree canopy. But in the preceding years, the number of trees planted has fallen far short of these objectives.
According to the SF Urban Forestry Council’s 2020 annual report, “The number of trees planted decreased significantly not only compared to fiscal year 2018-19, but also compared to all the previous five fiscal years.” In 2019-20, a total of 3,355 trees were removed, but only 2212 were planted. That’s a shortfall of over 1,000 trees.
But that’s not the whole picture.
A tree census conducted in The City found 124,795 street trees and 500 different species in 2017. (Trees in public parks and private property were excluded from the count.) However, estimates of street tree planting and removal by SFPW and Friends of the Urban Forest put the number of street trees at 121,310, as of June 30, 2020. That’s 3,485 fewer trees.
In April 2021, tree-planting exercises resumed in small groups, spearheaded by FUF and BUF. That’s good news, but not nearly enough. Back in 2016, San Francisco had 13.6 percent of urban tree canopy, which was one of the smallest of any large U.S. city. The City has become even less green since.
Enough studies have shown that leafy avenues are far more therapeutic than barren, concrete landscapes. As temperatures rise in the coming days, city leaders, corporate partners, and elected representatives must find the resources to increase San Francisco’s tree stock. An equitable plan for planting trees is a considerate approach to addressing climate challenges.
Jaya Padmanabhan is a guest columnist and her point of view is not necessarily that of The Examiner. Twitter: @jayapadmanabhan.