There's usually a pretty good explanation when LA's temperatures spike, some specific meteorological happening that we can single out and blame. But a new index out from the state's Environmental Protection Agency shows that LA, because of its highly urbanized state, also gets a significant added bump in temperatures from the heat island effect (the heat-collecting powers of concrete and paved roads that warm urban areas up more than rural areas nearby). In fact, the LA area gets "more additional heat than any other region, in part because of how urbanized it is," says KPCC.
The sprawly, built-up nature of the LA area makes it more of "an urban heat archipelago" than a lone heat island "because it's like a whole chain of urban heat islands that run into each other," a rep for the California EPA says. Some sections around LA get up to 19 degrees Fahrenheit hotter in the summer because of the heat trapped by their concrete and asphalt.
Research showed that the urban heat island effect sort of traced that of LA's ozone pollution in that "it moved east and settles against the hills." The highest temperatures were found east of Downtown, then blown inland to the valleys and contained near the base of the San Bernardino Mountains.
To put the phenomenon into hard numbers, researchers for the state's EPA used temperature records and models for California's cities, and then compared those numbers to temperatures from less urbanized areas nearby, like, say Bakersfield, which has high summer temperatures, too, but doesn't necessarily have "extreme heat islands" like a city would. The higher temperatures in cities gave the agency an idea of how much hotter urban areas were getting because of their heat-trapping surfaces.
The urban heat island effect has also been blamed for slowing doing away with LA's early morning and nighttime fog; when that goes away, it's been predicted that fire danger will rise and summers will get even hotter. The good news is that once scientists figure out where the effect is its strongest, work can begin on mitigating its effects through things like tree plantings and repainting roofs with colors that don't soak up as much heat.