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California's concrete shell is making its flooding much worse

The "atmospheric river" that has dropped weeks of rain on California is showcasing how much of the state is paved over.

California has spent the first weeks of the year dealing with a “parade of storms” that has left the Golden State distinctly waterlogged. Over the weekend, more precipitation slammed into the state, causing snow closures up in the mountains, flooding down in San Diego and a mudslide near Oakland. The state has had rainfall totals of 400% to 600% above average since Christmas, an amount that would likely overwhelm almost any region, especially one so parched after years of drought. But the severity of the flooding in California’s cities shouldn’t come as a surprise given how few places the deluge can go once it has fallen from the sky.

The problem isn’t a lack of science about the matter — it’s decades of poor planning.

Over the last century, the world has been increasingly covered with impermeable pavements like asphalt, tarmac and concrete to handle the rise of motor traffic. As of 2004, the total area of paved surfaces in the U.S. alone covered an area nearly the size of Ohio, a figure that has surely only increased since then. This growing shell over the planet is both contributing to climate change and exacerbating its effects, as we’re seeing now in California.

At this point, the problem isn’t a lack of science about the matter — it’s decades of poor planning. The Center for Watershed Protection has said that “as much as 65% of the total impervious cover in the landscape can be classified as ‘habitat for cars’” — which includes roads, parking lots, driveways and garages. Meanwhile, a group of researchers in 2020 estimated that for “every percentage point increase in roads, parking lots and other impervious surfaces that prevent water from flowing into the ground, annual floods increase on average by 3.3%.” And a 2013 study showed that Los Angeles was 61% covered with impervious surfaces at the time; San Francisco, which has been dealing with flooding for weeks now, was 54% paved over.

Even before the record precipitation in California, we already knew what happens when development overtakes the planet’s ability to absorb the brunt of extreme weather. When Hurricane Harvey struck Houston in 2017, the floodwaters from the storm killed dozens and displaced tens of thousands of people. Harvey was the perfect kind of storm to devastate the country’s fourth-largest city — massive and slow-moving, dumping 60 inches of rain over four days — and an example of the storms to come as climate change accelerates.

Houston’s metropolitan area is famous for its extensive sprawl, with only Atlanta’s boasting a lower population density, according to the 2010 census. The rush of construction that facilitated the “paving of Houston” has meant spreading out into the floodplains, prairie, rice fields and wetlands that once soaked up rainfall. It’s a problem that officials in Houston have been aware of for decades but had only barely acknowledged before Harvey. “They did not build the third reservoir, which was so badly needed. They built houses,” Richard Hyde, a retired petroleum geologist, told NPR in 2017. “Houses get tax money and reservoirs don’t.”

Worse, the actual act of paving our planet is fueling climate change. The cement needed to produce concrete is derived mainly from limestone, which contains both calcium and carbon dioxide. The process of extracting that calcium — which acts as a binding agent in cement —has made the industry responsible for around 8% of global carbon emissions. And all that concrete that has gone into building up our cities has also made them much hotter than surrounding areas, adding to the misery that rising temperatures are already causing.

California is at least aware of the problem, with several major cities working on rolling back the harm of concrete-ification. Los Angeles in particular has invested heavily in stormwater capture programs, including constructing dirt basins that allow rainfall to seep underground for later use. And around the country “urban planners are increasingly thinking of cities less as rain jackets—designed to whisk water away as fast as possible before it has a chance to accumulate—and more as sponges,” as Wired reported last year. That includes adding more green spaces and using so-called pervious pavers, which are laid with gaps to allow water to be filtered and absorbed rather than run off into rivers and cause them to overflow.

The hardening of the Earth’s surface is a perfect distillation of the forces driving climate change writ large.

It’s humbling to consider how many of the problems humanity faces in the coming decades spring from the inability to consider the consequences of our actions. The hardening of the Earth’s surface is a perfect distillation of the forces driving climate change writ large. Like the climate challenges we face, the solutions are less about science at this point than public policy. But a 2018 study found that things were trending in the wrong direction — tree cover in urban areas across the country was falling, and the number of impervious surfaces was increasing.

The storms that have inundated California will keep coming. In response, America in particular needs to condense the sprawl that our car-centric society has demanded, making transportation infrastructure more efficient. We need to continue to bring back spaces that can withstand the rain and invest in technology like cool pavements and pervious pavers to help minimize the damage. And, most important, we must crack the shell that threatens to help drown us all.