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Dangerous weather events with wind and rain have disproportionate effects on the socially vulnerable, according to new research.

from Northeastern University associate professor Serena Alexander studied "compound precipitation-wind extremes." The study is published in the International Journal of Climatology.

Most studies, Alexander says, "examine rain and wind separately, but we do know that when these are combined, or happen simultaneously, they can have greater impacts鈥攁nd they jointly affect, especially, socially vulnerable communities."

Compound precipitation-wind extremes, or CPWEs, "occur when we have heavy precipitation and strong winds that happen either simultaneously or within a short window," she continues. Either kind of event鈥攁 heavy downpour, high winds鈥攊s less dangerous and causes less damage on its own than when they occur together.

Most of the time, "we look at these hazards separately," Alexander says. One important takeaway from research of this kind "is that perhaps you should look at them simultaneously, on maps, in order to really understand the potential impacts."

The researchers gathered data from the past 40 years, looking specifically at San Francisco and California's Bay Area. They focused on the "most intense 2% of wet season days." Importantly, she notes, moderate weather events can still produce severe damage, especially in locations with lower-quality infrastructure鈥攍ike older buildings or undermaintained roads and waterways.

In fact, "the same storm can have drastically different consequences," Alexander cautions. The socioeconomic context matters. One community, with new homes and access to high-quality transportation, will almost by default have an easier, safer experience with an extreme weather event than a poverty-stricken neighborhood with older, lower-quality housing and less available transportation.

In cases of displacement, the socially vulnerable face a more "costly recovery for residents that might have very few financial buffers to cope with it."

Displacement is often the greatest threat to socially vulnerable communities, who might never be able to afford to rebuild, Alexander continues. After Hurricane Katrina, "many of the low-income individuals could not go back."

Why the Bay Area?

Alexander's interdisciplinary and intercollegiate research team looked to the Bay Area for a variety of reasons. One was the simple high availability of data, allowing them to observe a "five kilometer gridMET data set," she says, which helped "capture fine-scale climate variability across the nine Bay Area counties."

is a meteorological tool that captures weather patterns across the contiguous United States, beginning in 1979.

They could then overlay this tool with , which includes 15 variables, "things like income, age, housing, transportation, race and so forth," Alexander says.

The Bay Area is also home to "striking contrasts," she continues. From complex topography to diverse microclimates, "extreme wealth and extreme poverty. Sitting in this nine-county Bay Area, we have homeless encampments all the way to [some of] the wealthiest individuals in this country."

Their data also made clear that CPWEs are increasing not only in duration and intensity, but frequency.

Helping communities prepare

To protect those populations that are most at risk, even as CPWEs become more regular, Alexander foresees a variety of potential policy interventions. First and foremost, she stipulates that improving housing would do much to protect these populations, which "includes anything from retrofitting mobile homes" to upgrading infrastructure and maintaining drainage.

But emergency planning and communication systems also need significant improvement. She notes that vulnerable communities, especially homeless encampments, have not received fair warning about these dangerous weather events. "So we have to improve that," she says, and "make sure that such warnings are specifically reaching linguistically diverse, low-income, transit-dependent and potentially homeless residents as well."

"The interaction of physical hazard and social inequality determines greater risk," she concludes, calling it a nationwide issue. Newer infrastructure simply means "a better capacity to adapt if something happens."

This story is republished courtesy of Northeastern Global News .