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Roofs, streets and trees: How LA is trying to lower its temperature

Downtown Los Angeles hit 98 degrees on Saturday, breaking a temperature record that stood for 131 years. You better get used to it: the number of extremely hot days is expected to triple by mid-century. That’s why LA Mayor Eric Garcetti has the goal of lowering this urban heat island effect three degrees by 2035.  Can the city do it?

Like most big cities, Los Angeles literally creates its own climate. Buildings and asphalt absorb and radiate heat, raising summer temperatures by as much as 19 degrees in some parts of the region. According to CalEPA, LA has the worst urban heat island effect of any region in California.

Excessive heat is deadly. Heat stroke, heat exhaustion, difficulty breathing, cramping and general discomfort killed more people between 1979 and 2003 than hurricanes, lightning, tornadoes, floods and earthquakes combined, according to the Centers for Diseases Control and Prevention.

“Heat is the greatest weather -related public health threat,” said David Fink, the director of policy at Climate Resolve, which works on urban heat issues in LA.

L.A. is the one just two major cities worldwide with atemperature reduction target (the other is Melbourne).  Outlined earlier this year by Mayor Garcetti, there are three main components of the plan: replace roofs with less heat-absorbent roofing materials, repave or repaint city streets to make them more reflective and plant more trees.

Beginning in 2014, LA has had a “cool roofs” ordinance, which requires anyone building a new roof or replacing more than half of an existing roof to do so with reflective shingles.  Garcetti set a goal of having 10,000 cool roofs installed by the end of 2017. So far the city estimates there are 8,000. LA Department of Water and Power offers rebates of up to 30 cents per square foot.

Because the city is not compelling people to rip out their roofs, and because homeowners do not regularly replace roofs, it’s likely to take a quarter century to shift all the roofs in the city to the new, reflective material,  Fink said.

In late May, the Bureau of Street Services painted one block of Jordan Avenue in Canoga Park with a cool, gray paint. The bureau had previously tested out the paint on the Balboa Sports Complex in the San Fernando Valley to make sure cars wouldn’t skid and people wouldn’t slip, but the Jordan Avenue test was the first application on a street surface in the state.

Since then, the city has painted seven other blocks throughout West and South LA and elsewhere in the Valley. The goal is to paint a block in all 15 council districts by the end of the summer.

LA’s cool pavement program is not as far along as cool roof deployment, because the technology is much less advanced.

“This is very slow moving industry,” said Greg Spotts, assistant director of the Bureau of Street Services. “The materials used today to build and maintain streets are the same ones used in World War Two.”

However, Spotts said cool pavement was likely going to play a major part in LA meeting its temperature goals because the city has control over streets surfaces – unlike rooftops.

For this reason, roofs and trees are likely to be much easier areas in which to make progress, according to Fink.

Former Mayor Antonio Villaraigosa had a goal of planting one million trees (he got to 426,000 by March 2014). Mayor Garcetti, who doesn't share that numerical goal, has re-named the initiative “City Plants.” His administration has planted just over 58,000 trees so far.

Fink, whose organization worked with the city on the cool roofs ordinance, said the mayor’s office could set a target for tree planting and be more strategic about where trees go.

But tree-planting is clearly effective at reducing urban heat. According to a UCLA study, city blocks with more than 30 percent tree cover can be up to five degrees cooler than those with less tree cover. 

By lowering summertime temperatures, trees also help reduce energy used by running air conditioners, netting a savings of up to $119 million, according to the US Forest Service

This post has been updated at 9:33 am on July 11, 2017 with number of trees planted by mayors Garcetti and Villaraigosa.