Sat. Sep 24th, 2022
Flooding from Hurricane Sandy in 2012

Flooding from Hurricane Sandy in 2012

Christina Laughlin usually does everything she can to prevent the floods that plague her neighborhood in Norfolk, Virginia, on the Chesapeake Bay. But on a stormy Sunday morning in October 2019, she donned a windbreaker and wellies, grabbed her battered smartphone and deliberately headed straight for the high water mark.

Like them, hundreds of other locals were out that day, busy snapping photos of the water and linking them to GPS markers during the highest astronomical tide of the year, known as the ‘royal tide’. Norfolk is one of several coastal cities in the eastern US that has experienced a record rate of sea level rise, and scientists hope the data collected by these citizen scientists can help improve the ability to predict exactly when and where damaging flooding will occur. take place.

Low-lying cities like Norfolk are particularly vulnerable, says University of Western Ontario geographer James Voogt, one of the authors of a 2020 paper in the Environmental and Resources Annual Review on climate events in urban areas. “You have three things that work toward increasing a city’s vulnerability to flooding,” he says: sea level rise, increased likelihood of severe precipitation events, and an abundance of impervious surfaces that prevent water uptake and encourage runoff.

As early as 2050, climate scientists predict, the average high tide in the Norfolk area will equal the current royal tide. But it’s not just the mid-Atlantic: many other parts of the world will be increasingly prone to flooding, endangering lives and property. So understanding and accurately predicting flood risks associated with extreme weather and rising tides is a major challenge for vulnerable cities around the world.

If we don’t get the forecast just right, we’re preparing for a flood in the wrong places, says forecast scientist David Lavers of the European Center for Medium-Range Weather Forecasts, an independent research and weather forecasting organization that provides weather data and forecasts for 34 European countries. .

That’s where Laughlin comes in — and hydrologist Derek Loftis of the Virginia Institute of Marine Science, assisting Laughlin and others. In 2017, Loftis and colleagues started a project called Catch the King that uses a smartphone app to collect citizen scientists’ data during tidal waves. He will use that data to validate and improve his mathematical flood model called TideWatch for Norfolk and the surrounding area.

Loftis’ mission is simple: “I want to know where the water is going before it goes there,” he says. But as he and other scientists around the world know, it’s anything but easy to collect the necessary data and then process it quickly enough to make actionable forecasts.

Understanding the floods

The first step to making a forecast is a detailed understanding of the current weather situation. “You base your model on how the atmosphere works, and you start with conditions as they are now,” says hydrologist Hannah Cloke of the University of Reading in the UK. If this data isn’t accurate and detailed, she says, the model probably won’t be very good.

Accurate flood forecasting also requires an understanding of the ground situation: physical factors such as river water flow, elevation, soil saturation and land cover. By the early 2000s, supercomputing was so advanced that hydrologists and geologists were able to integrate weather forecasting models with such measurements. But when Loftis started working on flood forecasting about a decade ago, scientists still didn’t have the fine-grained water level measurements that accurate forecasting needs, nor the all-important ability to predict fast-moving floods in real time.

To address this shortcoming, Loftis developed a forecasting model based in part on detailed city government maps and high-resolution surveying with LiDAR, which uses pulsed laser beams to create a 3D map of the Earth’s surface. By testing his predictions against past floods, he showed that his calculations were broadly accurate.

But he needed real-life information about flooding to refine his models. So in 2017, he and his colleagues set up an array of 28 internet-connected water level sensors in communities around the Norfolk area, similar to systems used in Taiwan and the UK. The new sensors, combined with devices previously installed by the National Oceanic and Atmospheric Administration and the US Geological Survey, relayed raw measurements of water height and movement to a series of supercomputers at the Virginia Institute. Some towns in the area are already using data from the sensors to warn residents about flooding.

Around the world, hydrologists like Loftis are trying to predict flooding, with each region facing its own challenges. Countries with less resources still struggle with the kind of data dearth the US once had. And without proper input, scientists can’t build accurate models, says artificial intelligence expert Sella Nevo, chief engineer of the Google Flood Forecasting Initiative, which uses artificial intelligence to estimate when and where flooding will occur.

“Knowing that there was a flood in the Ganges is easy,” says Nevo. “But knowing to within 10 meters which areas were wet and which were not is a challenge.” And without that level of detail, he says, the forecast won’t help the people on the ground.

Like Loftis, Nevo’s team uses data from flow meters to track current water levels and how they’re changing over time. Their fledgling initiative started with creating a flood forecast for India, using more than 1,000 smart power meters deployed across the country by the Indian Central Water Commission. Next, the team had to create fine-grained 3D digital elevation maps of the land. Existing elevation models didn’t have enough detail, so the group created their own by performing some math wizardry on available satellite imagery.

With these two streams of information, Nevo and colleagues have built an inundation model of what will happen if, for example, a river overflows its banks. This inundation model combines physics-based calculations and machine learning to produce flood forecasts that can predict water levels within 15 centimeters 90 percent of the time.

But models like these are all theoretical until tested with real data. And that’s where projects like Catch the King come into play.

Holding back the tide

Loftis designed its flood forecast to save lives during hurricanes and other severe weather events that are expected to increase as the climate continues to warm. But he needed a way to test his calculations when lives weren’t at stake.

He got his chance when Dave Mayfield, a retired reporter with the… Virginian pilot newspaper in Norfolk, approached the Virginia Institute of Marine Science about setting up a project to raise awareness about climate change and the effects of sea level rise in the area. Together they launched Catch the King in 2017. They put together a team to design an app called Sea Level Rise that allows users to map flood marks using their smartphones.

And then they got it out through the local media. In their inaugural year, more than 700 volunteers were found to chart the royal tide – the effort in the Guinness Book of World Records as the most contributing environmental research ever — and Loftis used the data to validate its street-level flood forecasting model.

Since then, hundreds of volunteers have shown up for Catch the King every year — including about 200 this year despite the pandemic — to help Loftis continue to refine its predictions. “The more data we have, the better we can meet the challenge of sea level rise and climate change,” he says. But that’s only part of the problem solved. Another major challenge for him and other forecasters is to ensure that their detailed, high-resolution forecasts are available with enough notice for residents and governments to take action before flooding begins.

Currently, TideWatch offers detailed predictions up to 36 hours in advance. Ideally, by continuously refining its models, Loftis hopes to make reliable predictions up to 72 hours in advance. Another flood forecasting system developed by researchers at George Mason University provides comparable predictions up to 84 hours in advance for residents of the Washington, DC area.

Other vulnerable parts of the US want to join in. “Knowing where it might flood two or three days in advance would be incredibly valuable,” said Peter Singhofen, CEO of Streamline Technologies, Inc., and a flood modeling expert in Florida. “We can evacuate people. We may be able to change the way we operate infrastructure, such as water pumping stations, to potentially prevent flooding in some areas or protect property and lives.”

The Google Flood Forecasting Initiative has also made progress. The project has global ambitions, but for now, Nevo’s work has focused on the monsoon-prone Patna region of northeast India. Last year, the model provided accurate flood warnings for incoming monsoons and cyclones in advance – a major step forward for the region. In June, Google expanded its forecasting to all of India and is starting work on forecasting for Bangladesh.

Better understanding how climate change can affect flooding patterns is critical, says climate scientist Megan Kirchmeier-Young of Environment and Climate Change Canada, a government agency that promotes sustainability. “As we continue to warm, we will see a continued increase in the frequency and severity of heavy rainfall over North America,” she says — and that means more flash flooding.

Loftis expects these changes for the Norfolk region to come into play. As the water level rises, more streets will be flooded, or even impassable, over a longer period of time. All this means that making an accurate flood forecast is a never-ending task as the rising waterline of the Atlantic Ocean slowly but surely reclaims increasing swaths of coastal cities.


Carrie Arnold is an independent public health reporter from Virginia. Follow her on Twitter and Instagram at @edbites

This article originally appeared in Known magazine, an independent journalism company of Annual Reviews. Sign up for the newsletter View Reset—An ongoing series examining how the world is coping with the coronavirus pandemic, its consequences, and the way forward.

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