CAMBRIDGE, Mass. – Coastal cities and communities will face more frequent major hurricanes in the coming years as the climate changes. To help coastal cities prepare for future storms, Massachusetts Institute of Technology scientists have developed a method to predict how much flooding coastal areas will experience as hurricanes evolve over the next few decades. did.
When a hurricane makes landfall, strong winds kick up salty ocean water, creating storm surges in coastal areas. As the storm moves overland, torrential rain could cause further flooding inland. The interaction of multiple flood sources, such as storm surge and rainfall, further increases the risk of hurricanes and can result in far more flooding than from a single flood source alone. A new study introduces a physics-based method to predict how these complex and compound flood risks will evolve in a warming climate for coastal cities.
An example of the effects of compound flooding is the aftermath of Hurricane Sandy in 2012. Strong winds drove storm surge, combined with rainfall flooding in some areas, and the storm made landfall on the U.S. East Coast, causing historic flooding. Devastating floods hit New York and New Jersey.
In the study, the MIT team applied a new complex flood modeling approach to New York City to predict how climate change will affect the risk of complex floods from hurricanes like Sandy in the coming decades.
They found that in the current climate, a combined sand-level flood is likely to hit New York City every 150 years. By mid-century, a warming climate will increase the frequency of such floods every 60 years. By the end of this century, devastating Sandy-like floods will flood cities every 30 years. This is a five-fold increase compared to the current climate.
“Long-term average damages from weather disasters are typically dominated by rare and intense events like Hurricane Sandy,” said study co-author Kerry Emanuel, professor emeritus of atmospheric sciences at the Massachusetts Institute of Technology (MIT). he says. “It's important to understand these correctly.”
Although these are grim predictions, researchers hope the flood predictions will help city planners prepare for and protect against future disasters.
Study author Ali Sarhadi said: “Our methodology provides coastal city authorities and policy makers with a complex hurricane flood risk assessment for coastal cities, down to each street and building, now and for decades to come. “It provides important tools for implementation at a detailed and granular level.” , a postdoctoral fellow in MIT's Department of Earth, Atmospheric, and Planetary Sciences.
The team's open access research is published online today in the Proceedings of the American Weather Society. Co-authors include Raphael Rousseau-Rizzi of the MIT Lorenz Center, Kyle Mandli of Columbia University, Jeffrey Neal of the University of Bristol, Michael Wiper of Université Charles III de Madrid, and Monika Feldmann of the Swiss Federal Institute of Technology Lausanne. included.
seeds of flood
To predict regional flood risk, weather modelers typically look to the past. Historical records contain measurements of wind speed, rainfall, and spatial extent from past hurricanes, and scientists use this information to predict where and how much flooding will occur in future storms. Predict what will happen. But Sarhadi believes the limitations and brevity of these historical records are insufficient to predict future hurricane risk.
“Even if we had a long historical record, it would not be a good guide to future risks from climate change,” he says. “Climate change is changing the structural characteristics, frequency, strength and movement of hurricanes, and we cannot rely on the past.”
Sarhadi and his colleagues instead focused on using physics-based risk assessment techniques to predict a region's risk of hurricane flooding under a changing climate. They first combined simulations of hurricane activity with long-term coupled models of the ocean and atmosphere. Emanuel developed his own hurricane simulations. Using his simulations, the researchers virtually dispersed tens of thousands of hurricane “seeds” into the simulated climate. Most species disappear, but some species grow into category-level storms, depending on ocean and atmospheric conditions.
When the team runs these hurricane simulations using climate models of ocean and atmospheric conditions under specific global temperature projections, they can predict how hurricanes will behave under past, current, and future climate conditions, such as intensity, frequency, and size. You can see how it changes in terms of.
The team then sought to accurately predict the level and severity of combined flooding from future hurricanes in coastal cities. The researchers first used a rainfall model to simulate the rain intensity of a number of simulated hurricanes, then applied a numerical model to predict the rain intensity based on information about the region, such as its surface and topographic features. The rainfall intensity was hydraulically converted into surface flooding during hurricane landfall. . They also used a hydrodynamic model to convert the hurricane's maximum wind speed and sea level pressure to storm surge height in coastal areas, simulating the same hurricane's storm surge. This simulation further evaluated the propagation of seawater into coastal areas and caused coastal flooding.
The team then developed a computational fluid dynamics model to determine how two sources of hurricane flooding, such as storm surge and rain flooding, occur simultaneously through time and space as a simulated hurricane makes landfall in a coastal region such as New York. We predicted how they would interact. Cities in current and future climates.
“There is a complex nonlinear hydrodynamic interaction between salt water surge flooding and freshwater rainfall flooding, creating a complex flood that many existing methods ignore,” Sarhadi says. . “As a result, they underestimate the risk of compound flooding.”
amplified risk
After establishing the flood prediction method, the team applied it to a specific test case: New York City. They used a multifaceted approach to predict the risk of combined urban flooding from hurricanes, and more specifically hurricanes like Sandy, in the current and future climate. Their simulations show that the chance that the city will experience a Sandy-like flood will increase significantly in coming decades as the climate warms, from once every 150 years in today's climate to one in 150 years by 2050. It is expected to occur once every 60 years, and by 2099 this will increase to once every 30 years.
Interestingly, much of this increased risk has more to do with how sea levels rise around the world than with how hurricanes themselves change as the climate warms, the study found. It was discovered by the people.
“In the coming decades, coastal areas will experience sea level rise. We also incorporated that effect into the model to see how much it increases the risk of compound flooding,” Sarhadi explained. do. “And we actually see that sea level rise is playing a major role in amplifying the risk of combined hurricane flooding in New York City.”
The team's methodology can be applied to any coastal city to assess the risk of combined flooding from hurricanes and extratropical storms. Sarhadi said this approach will enable decision-makers to make informed decisions about implementing adaptation measures, such as strengthening coastal defenses to strengthen the resilience of infrastructure and communities. I'm looking forward to it.
“Another aspect that highlights the urgency of our research is that coastal populations are projected to increase by 25 percent by mid-century, which will increase exposure to harmful storms.” says Sarhadi. “Furthermore, with trillions of dollars of assets in coastal flood-prone areas, proactive strategies are needed to reduce the damage from combined hurricane flooding in a warming climate.”
This research was supported in part by Homesite Insurance.
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