This story Originally by wired And copied here as Climate Service Desk Cooperation.

Think back to the child on the beach, building a fence around the sand castle. If you design these fortifications correctly, the tide will flood into your kingdom, and then before the walls are finally eroded away. By redirecting the rising water, you could have saved your castle-at least for a while.

Think bigger now. Imagine you are an urban planner in an area threatened by rising sea levels, and you have spent a lot of money to build a suitable seawall. When the tide comes, the wall is stabilized, saving you billions of dollars in property damage. but: Ho ho ho. Like the waves you once redirected around your sandcastle, rising water hits the walls and flows into the communities on either side of you. You saved your residents, but endangered others.

The new model shows how disastrous this wayward water phenomenon can be in the San Francisco Bay Area, where sea levels may rise 7 feet in the next 80 yearsAnne Guerry, chief strategy officer and chief scientist of the Natural Capital Project at Stanford University, said: “These rising water levels put millions of people and billions of dollars in buildings at risk,” she co-authored paper Describe the research.It was published this week in the Proceedings of the National Academy of Sciences. “A new feature of this work is that people don’t necessarily think about how communities, such as the Bay Area, connect with each other through these shared waters,” she continued.

Guerry and her colleagues divided the coastline into multiple parts based on geological and other characteristics for modeling. Then they used a hydrological model to show where the rising water would flow if a seawall was set on a given part of the coastline. Basically, they imagined what would happen if the residents of an area decided to protect themselves without fully considering the resulting hydrology. “The water must flow somewhere,” Gary said. “We found it would eventually flow into other communities, making their flooding worse. ”

They also combined economic models to calculate how much damage this would cause. For example, they estimate that if the local government builds a wall around the city of San Jose in the South Bay, it will flood other communities with rerouted water equivalent to 14,400 Olympic-sized swimming pools. San Jose will be saved, but the nearby Redwood City and other communities will be messed up. Guerry said: “This is equivalent to a high tide in the spring when the water level is naturally highest, and you need to pay an additional $723 million in flood damage.” “This is just building a large seawall in a small part of the bay.” And this exceeds 7 The billion-dollar figure does not take into account the potential damage to ecosystems and fisheries, so this figure is conservative.

The extra water pushed back by the walls of San Jose will even accumulate in the bays of Napa and Sonoma, 50 miles to the north. The damage will also be reversed: If the coasts of Napa and Sonoma are fenced off, the South Bay will suffer tens of millions of dollars in damage.

This is not good news, considering that humans have the habit of building large cities along the coast, and now city planners must do this Fortify, And seawalls are usually the best defense. The author of this paper pointed out that by 2100, the United States alone is expected to spend 300 billion U.S. dollars on supporting coastlines to prevent sea level rise and greater waves caused by storms. More powerful Due to climate change. Legislators must consider as soon as possible whether to spend $26 billion to quarantine the surrounding area of ​​Houston. Jakarta also needs to build a huge seawall, but it cannot be in the land below it Stop sinking.

So far, policymakers have assumed Laura Feinstein, director of sustainability and resilience policy at SPUR, a non-profit public policy organization in the Bay Area, said that seawalls may have a negative impact on nearby communities, but this new study provides potential harm digital. (She was not involved in this research.) “This is a truly quantitative and rigorous proof of what people have always said about sea level rise, that the area is either sinking or swimming together,” she said. “If a region invests resources to protect its coastline, it will only exacerbate the sea level rise of its neighbors.”

But getting local governments to act in concert can be a challenge, especially if they don’t all have the same financial resources, or some places face special pressure from lucrative local industries that do prefer not to get into trouble. The temptation for a county with a healthy tax base (pronounced: rich man’s county) would be to unilaterally build seawalls, damn low-income neighbors.

In the Bay Area, income inequality is severe (the gap between average high income and low income) Is 263,000 USD, Compared to US$178,000 nationwide), the site is ready for disaster. “For decades, communities of color and low-income communities have been pushed into the low-lying areas of the Bay Area,” Feinstein said, referring to shoreline communities in cities such as Oakland and East Palo Alto. Many of these areas are also historically home to manufacturing, warehousing, shipping, and railway industries. “Old toxic dumps, heavy industry and transportation, and low-income communities of color are most vulnerable to rising sea levels in the Bay Area,” she said. When the water level rises, they can push up the groundwater contaminated by these buried toxins; not only will floods occur in these areas, but contaminated water may be used.

Some seawalls in the Bay Area are already under construction.The Port of San Francisco is Upgrade its century-old Embarcadero seawall, The U.S. Army Corps of Engineers is studying how to Strengthen the embankment of San Francisco International Airport. Foster City to the south is Build a new embankment This will stretch for more than 6 miles, and the sewage treatment area in North Richmond on the other side of the bay is Consider your own dike project.

At present, local governments do not have to jointly consider the unintended consequences of the future seawall. “This is mainly because there is no formal mechanism for people to do this,” said Dana Brechwald, manager of the San Francisco Bay Conservation and Development Commission’s Adaptation Program for Rising Tides, who was not involved in the new research. (She is also the project manager of Bay Adapt, a regional cooperation project that advocates protecting humans and ecosystems from rising sea levels.) “If someone wants to do this at the local level, it will be completely voluntary.”

However, if seawalls are built randomly or without cooperation, by digitizing the severity of flooding, the new model may encourage more cooperation between neighboring countries. “We really want to set up this kind of thing in the future,” Brechwald added. “These mechanisms are very important to ensure that we have a fair adaptation.”

It may also allow planners to consider alternatives to walls. Nature has actually prepared another solution: using the landscape to bring us benefits. (Climate scientists call it Nature-based solutions, Because it uses natural processes instead of trying to solve problems through design. )

Certain coastlines naturally absorb seawater better than others—for example, alluvial valleys, floodplains where rivers meet the sea. These have sandy, muddy bottoms that absorb water like sponges, especially when compared to rocky coastlines. Guerry argued that instead of separating them, we should drain the water. Towards They, so they can be used as overflow areas. “Sometimes, it is more practical and economical to choose strategically achievable areas. absorb Water,” she said. “These can be things like swamps and ponds, but they can also be parks and golf courses or other types of semi-natural areas where intermittent flooding will cause less damage. ”

“Seawalls are not the only way to deal with rising sea levels,” Guerry added, “although this is a traditional preferred solution.”


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