Cool Roofs Can Help Shield California’s Cities Against Heat Waves

An interesting article that discusses how cool roofs can be used as a guard against the increasing temperatures due to climate change. Californian’s must find cost effective ways to adapt to the changing weather conditions.

By Priyanka Runwal

This summer alone, intense heat waves have been to blame for at least 11 deaths in Japan, a record-breaking 45.9-degree Celsius temperature in France, and a heat advisory affecting 147 million people on the U.S. East Coast. Conjectured as the “new normal,” these extreme air temperatures can heat our bodies, causing sunstrokes or even organ damage.

A new study by researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) shows that if every building in California sported “cool” roofs by 2050, these roofs would help contribute to protecting urbanites from the consequences of these dangerous heatwaves. Their study, “Interacting implications of climate change, population dynamics, and urban heat mitigation for future exposure to heat extremes,” was recently published in the journal Environmental Research Letters.

The researchers predict that heat waves are likely to become two to 10 times more frequent across the state by mid-century. But if cool roofs were adopted throughout California’s most populous areas – the San Francisco Bay Area, Los Angeles, San Diego, and Sacramento – by 2050 these reflective roofs could bring down heat wave exposures (defined as each time a person experiences a heat wave) by 35 million each year, compared to an estimated 80 million heat wave cases in 2050 with no increase in cool roof adoption. This is the latest example of Berkeley Lab’s research into the potential for reflective roofs, walls, and pavements to mitigate urban heat, reduce air conditioning usage, and save water.

City dwellers are more vulnerable than their rural counterparts to a heat wave’s negative effects. Due to the urban heat island effect, air temperatures spike several degrees higher in cities than in surrounding vegetated areas. Built surfaces readily absorb daytime heat and release it at night, keeping cities warmer overnight as well.

In this new study, the Berkeley Lab researchers had two goals. First, they wanted to predict heat wave occurrences across California’s 29 major urban counties between now and 2050. They used regional climate conditions between 2001 and 2015 as a starting point to simulate mid-century climate under two global warming scenarios.

Combining these climate conditions with high-resolution satellite images allowed them to incorporate urban features like buildings, roads, and vegetation, which absorb and release heat, and for more accurate future climate predictions. Then, the researchers used county-level population estimates for 2050 to assess population exposure to future heat waves.

Coating roofs white or installing sunlight-reflecting tiles in urban clusters could be one solution, according to the researchers.

“It’s not necessarily a complicated or costly technology,” Vahmani said. “But cool roofs, in general, are more effective if everyone adopts them.”

The second goal of their study was to analyze the effectiveness of cool roofs in mitigating heat wave impacts. To do that, the research team repeated the same high-resolution regional climate simulations, only this time replacing all existing building roofs with cool roofs. Specifically, they wanted to know if the increased solar reflectance might shield urban populations against heat waves.

They found that if every building in California sported cool roofs by 2050, it could bring down the annual number of heat wave exposures in California to 45 million from 80 million .

But the positive effect of cool roofs will be limited to reducing day time temperatures when the roofs reflect sunlight. At night, when roads and packed buildings slowly release heat, these roofs aren’t capable of directly providing cooling benefits.

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