Category: Floods

As sea levels rise, buying a coastal home is risky. What if you rented one from the government?

Read the full story at Fast Company.

More frequent flooding will make coastal areas uninhabitable. How can the government help residents manage that risk—and prepare for those floods?

Washington’s Famed Tidal Basin and Cherry Trees Face Rising Waters

Read the full story at e360 Digest.

Washington, D.C.’s Tidal Basin, flanked by rows of the city’s celebrated cherry trees, is facing a growing threat from rising seas and land subsidence.

The peak bloom of the Basin’s cherry trees, which occurred several days ago, traditionally draws hundreds of thousands of visitors annually. But this year and last, waters breached the Tidal Basin’s sea walls in places at high tide, according to The Bay Journal, which covers issues related to the Chesapeake Bay. The Bay Journal said that some paths along the Basin were flooded, while other were cratered or eroded by intruding waters. The rising waters also have killed some cherry trees closest to the Tidal Basin.

How to make sure Biden’s infrastructure plan can hold up to climate change – and save money

In the Netherlands, some flood control systems are designed to adapt to future climate change. Dutch Ministry of Infrastructure and Water Management

by Jeremy Bricker (University of Michigan)

The Biden administration is proposing a massive infrastructure plan to replace the nation’s crumbling bridges, roads and other critical structures. But to make those investments pay off, the U.S. will need designs that can endure the changing climate.

Most U.S. infrastructure is designed to stand for decades, including through what engineers expect to be rare storms and floods.

However, extreme storms that were considered rare a few decades years ago are already becoming more common. Hurricane Harvey in 2017 was the Houston area’s third “500-year flood” in three years, and it was followed by two more major flooding events.

Building infrastructure today that will be strong enough to manage the extreme scenarios the nation might see a century from now can be expensive. But what if infrastructure were instead designed to meet shorter-term needs and also be easily adapted later for the future climate?

I’m a hydraulic and coastal engineer who has been working on infrastructure design in the Netherlands, where dams and storm surge barriers are being designed to be adaptable. The methods there hold lessons for the U.S. as it prepares for a wave of new construction.

The problem with building for 100-year floods

Bridges in the U.S. are typically designed to allow the unimpeded passage of floods that have a 1-in-100 chance of happening each year. Similarly, a dam spillway might be built to handle a 10,000-year flood, and stormwater drains for two-year rainfall events.

These “return periods” are traditionally calculated using a method based on historical statistics that assume the climate doesn’t change much.

Water is released from the dam
During Hurricane Harvey’s extreme rainfall, water was released from Houston’s Barker Reservoir to protect its dam and upstream neighborhoods. Downstream neighborhoods flooded as a result. Win McNamee/Getty Images

In a warming climate with more extreme rainfall, worsening droughts and rising sea levels, these historical statistics can underestimate the intensity of future floods. That puts critical infrastructure, homes and lives in danger.

Putting adaptive design to work

The Dutch are masters of flood control. When about a third of a country sits below sea level, it becomes a necessity. U.S. engineers have been turning to them for advice in recent years as understanding of climate change and its impact on storms and sea level rise increases.

The Netherlands’ innovative designs, like the giant gates of the Maeslant flood defense, are getting noticed, but equally important is how the Dutch use adaptive designs to prepare for the future and keep costs under control.

The Maeslantkering protects The Hague, Rotterdam and other cities from high tides from the North Sea.

To see adaptive design at work, look at the renovation underway of the Afsluitdijk, a 20-mile-long dam that protects Amsterdam’s port from storm surges on the North Sea.

When the dam was completed in 1932, it drained river water to the sea by gravity at low tide. However, sea level rise, combined with the need to keep the water level in Amsterdam’s port low to protect the city, are making drainage by gravity alone increasingly ineffective.

To update the dam, the Dutch have built pump stations for draining water into the North Sea. Importantly, the new design reserves enough land to expand the existing pump stations or build new ones when future storms and sea level rise make it necessary.

Aerial view of the dam
The sluice gates in the center of the image allow water to pass through the Afsluitdijk between the IJsselmeer and the North Sea. The lock to the left of the sluice gates raises and lowers boats. Marcus van Leeuwen/Flickr, CC BY-SA

Lessons as the U.S. plans new coastal protections

Several U.S. cities, including Houston, New York and Boston, are now considering hurricane defense systems, and the future protection they will actually need to prevent flooding is unknown at this point.

By using adaptive design, they could include room for expanding those defenses as the climate changes.

That might mean building earthen dams and levees wide enough to allow for raising them when necessary, and reserving land for widening and heightening of coastal dunes that form part of the system and for adding pump infrastructure.

Crucially, movable storm surge barriers, which typically make up a short section of a barrier system, offer protection only from sporadic hurricanes and not from long-term sea level rise. The movable barriers may eventually need to be replaced with a dam, shipping lock and drainage pumps – that, too, can be planned for.

Map of South Boston showing flood risk
This map of Boston shows future flood risks if no protective measures are taken. City of Boston

By starting with an adaptive design, the U.S. can save billions of dollars compared with having to build new systems decades down the road. The recent renovations of California’s Folsom Dam, built in 1955, illustrate that cost. A new spillway completed in 2018 cost $900 million – with inflation, that’s about the original cost of the entire dam.

Adapting for Mississippi River flooding

When Dutch engineers plan new levees, storm surge barriers and river locks, they consider what are known as the Delta Scenarios – four possible futures for flood risk and sea level rise, ranging from moderate to extreme global warming. These scenarios create a framework for adaptive design.

For example, a complex of locks on the Meuse River, used to raise and lower ships and barges as they travel up- or downstream, needs to be replaced or rehabilitated. A new lock complex must have enough sluice gates, which can be closed or opened to allow high water through after storms, so the water doesn’t flood surrounding farms and cities. The accompanying weir – the low dam that raises the river’s level – must be high enough to retain enough water for ship operations during times of drought.

Building a tall weir with many sluice gates, and raising riverbank levees to match, would allow the lock complex to manage future climate scenarios, but that would be expensive. With adaptive design, the complex can instead be built to be easily modified later to meet changing climate needs. That includes reserving space for additional sluice gates, and designing gates that can be made taller by welding on additional components as needed.

On the Mississippi River and its tributaries, many of the old lock complexes that raise and lower the barges carrying agricultural products and industrial materials are now undergoing replacement. Using similar adaptive design techniques would be a cost-efficient way to face an uncertain future.

Jeremy Bricker, Associate Professor of Civil and Environmental Engineering, University of Michigan

This article is republished from The Conversation under a Creative Commons license. Read the original article.

FEMA unveils new flood insurance calculation it says will be more equitable

Read the full story at The Hill.

The Federal Emergency Management Agency (FEMA) on Thursday unveiled changes to the National Flood Insurance Program that it says will be aimed at being more equitable. 

A fact sheet from the agency said that it will be able to do this by calculating premiums based on home value and flood risk, with more expensive homes potentially costing more to insure.

The agency said that currently people with lower-valued homes are “paying more than their share of the risk” while those with higher-value homes are paying “less than their share.”

The Tide Is High—and Getting Higher

Read the full story in Wired.

A trove of historic records show that dredging and sea level rise are making nuisance high tides worse along the US coasts.

A Looming Disaster: New Data Reveal Where Flood Damage Is An Existential Threat

Read the full story from NPR.

Sea level rise and heavier rainstorms driven by global warming are sending more water into residential neighborhoods from the Gulf Coast to New England to Appalachia to the Pacific Northwest. And new data make it clear that many households and communities cannot afford the mounting costs.

More than 4 million houses and small apartment buildings across the contiguous U.S. have substantial risk of expensive flood damage, according to data released by the First Street Foundation, a nonprofit research organization that studies flood risk and housing. The cost of flood damage to homes nationwide will increase by more than 50% in the next 30 years, the First Street Foundation estimates.

Flood-prone homeowners could see major rate hikes in FEMA flood insurance changes, new study finds

Read the full story in USA Today.

With a major overhaul of the nation’s flood insurance program just months away, new data released Monday by the First Street Foundation suggests hundreds of thousands of homeowners in the riskiest locations across America could face massive rate hikes starting in October.

DOD Announces Release of the DOD Regional Sea Level Database

The Department of Defense Strategic Environmental Research and Development Program and Environmental Security Technology Certification Program has announced the public release of the DOD Regional Sea Level database.  

Making the information available broadly “is a critical requirement for its use in our Unified Facilities Criteria program for planners and designers,” said Thadd Buzan, Assistant Director for Military Construction, Office of the Assistant Secretary of Defense (Sustainment). 

Public access to the database allows for the integration of future sea level change information by contracted third parties such as engineering firms in their efforts to provide installation and facilities planning and design services for coastal locations. The database and its accompanying report, Regional Sea Level Scenarios for Coastal Risk Management, were developed by the DOD-led Coastal Assessment Regional Scenario Working Group to provide a consistent, authoritative approach to account for changing sea levels at DOD sites worldwide.  

Use of DRSL information is now incorporated into the department’s installation master planning criteria and civil engineering design criteria for coastal locations. When using the DRSL database, planners and designers must apply the planning horizon and regional scenario appropriate to the installation requirement, and the vertical datum (such as the North American Vertical Datum of 1988) appropriate to the location.

For more information on the DOD program, visit the SERDP-ESTCP website.

Webinar: Flood Resilience in the Year Ahead: Opportunities for the New Congress

Friday, March 5, 2021, 10-11 am CST
Register here.

Join experts, officials for webinar discussion of how federal policy can support state and local efforts to limit losses and recovery costs.

Atmospheric river storms can drive costly flooding – and climate change is making them stronger

Atmospheric rivers deliver rain to California in 2017. NASA

by Tom Corringham (University of California San Diego)

Ask people to name the world’s largest river, and most will probably guess that it’s the Amazon, the Nile or the Mississippi. In fact, some of Earth’s largest rivers are in the sky – and they can produce powerful storms, like the one now soaking California.

Atmospheric rivers are long, narrow bands of moisture in the atmosphere that extend from the tropics to higher latitudes. These rivers in the sky can transport 15 times the volume of the Mississippi River. When that moisture reaches the coast and moves inland, it rises over the mountains, generating rain and snowfall and sometimes causing extreme flooding.

Atmospheric rivers are an important water source for the U.S. West. NOAA

In the past 20 years, as observation networks have improved, scientists have learned more about these important weather phenomena. Atmospheric rivers occur globally, affecting the west coasts of the world’s major land masses, including Portugal, Western Europe, Chile and South Africa. So-called “Pineapple Express” storms that carry moisture from Hawaii to the U.S. West Coast are just one of their many flavors.

My research combines economics and atmospheric science to measure damage from severe weather events. Recently I led a team of researchers from Scripps Institution of Oceanography and the Army Corps of Engineers in the first systematic analysis of damages from atmospheric rivers due to extreme flooding. We found that while many of these events are benign, the largest of them cause most of the flooding damage in the western U.S. And atmospheric rivers are predicted to grow longer, wetter and wider in a warming climate.

Rivers in the sky

On Feb. 27, 2019, an atmospheric river propelled a plume of water vapor 350 miles wide and 1,600 miles long through the sky from the tropical North Pacific Ocean to the coast of Northern California.

Just north of San Francisco Bay, in Sonoma County’s famed wine country, the storm dumped over 21 inches of rain. The Russian River crested at 45.4 feet – 13.4 feet above flood stage.

For the fifth time in four decades, the town of Guerneville was submerged under the murky brown floodwaters of the lower Russian River. Damages in Sonoma County alone were estimated at over US$100 million.

Events like these have drawn attention in recent years, but atmospheric rivers are not new. They have meandered through the sky for millions of years, transporting water vapor from the equator toward the poles.

In the 1960s meteorologists coined the phrase “Pineapple Express” to describe storm tracks that originated near Hawaii and carried warm water vapor to the coast of North America. By the late 1990s atmospheric scientists had found that over 90% of the world’s moisture from the tropics and subtropics was transported to higher latitudes by similar systems, which they named “atmospheric rivers.”

In dry conditions, atmospheric rivers can replenish water supplies and quench dangerous wildfires. In wet conditions, they can cause damaging floods and debris flows, wreaking havoc on local economies.

After an atmospheric river event that caused severe flooding in Chile, sediment washed down from hillsides into the Itata River can be seen flowing up to 50 kilometers from the coast. NASA Earth Observatory

Helpful and harmful

Researchers have known for some time that flooding due to atmospheric rivers could cost a lot of money, but until our study no one had quantified these damages. We used a catalog of atmospheric river events compiled by Scripps Institution of Oceanography’s Center for Western Weather and Water Extremes, and matched it to 40 years of flood insurance records and 20 years of National Weather Service damage estimates.

We found that atmospheric rivers caused an average of $1.1 billion in flood damages yearly in the western U.S. More than 80% of all flooding damages in the West in the years we studied were associated with atmospheric rivers. In some areas, such as coastal northern California, these systems caused over 99% of damages.

Our data showed that in an average year, about 40 atmospheric rivers made landfall along the Pacific coast somewhere between Baja California and British Columbia. Most of these events were benign: About half caused no insured losses, and these storms replenished the region’s water supply.

But there were a number of exceptions. We used a recently developed atmospheric river classification scale that ranks the storms from 1 to 5, similar to systems for categorizing hurricanes and tornadoes. There was a clear link between these categories and observed damages.

Atmospheric River category 1 (AR1) and AR2 storms caused estimated damages under $1 million. AR4 and AR5 storms caused median damages in the 10s and 100s of millions of dollars respectively. The most damaging AR4s and AR5s generated impacts of over $1 billion per storm. These billion-dollar storms occurred every three to four years.

A moister atmosphere means worse storms

Our most significant finding was an exponential relationship between the intensity of atmospheric rivers and the flood damages they caused. Each increase in the scale from 1 to 5 was associated with a 10-fold increase in damages.

Several recent studies have modeled how atmospheric rivers will change in the coming decades. The mechanism is simple: Greenhouse gases trap heat in the atmosphere, warming the planet. This causes more water to evaporate from oceans and lakes, and increased moisture in the air makes storm systems grow stronger.

Like hurricanes, atmospheric rivers are projected to grow longer, wider and wetter in a warming climate. Our finding that damages increase exponentially with intensity suggests that even modest increases in atmospheric river intensity could lead to significantly larger economic impacts.

Scientists have developed a scale for categorizing atmospheric rivers that reflect both their replenishing capacities and their dangerous effects.

Better forecasting is critical

I believe that improving atmospheric forecasting systems should be a priority for adapting to a changing climate. Better understanding of atmospheric rivers’ intensity, duration and landfall locations can provide valuable information to residents and emergency responders.

It also is important to discourage new construction in high-risk areas and help people move to safer locations after major disasters, rather than rebuilding in place.

Finally, our study underlines the need to reduce global greenhouse gas emissions. These storms will keep coming, and they’re getting stronger. In my view, stabilizing the global climate system is the only long-term way to minimize economic damage and risk to vulnerable communities.

Tom Corringham, Postdoctoral Scholar in Climate, Atmospheric Science and Physical Oceanography, University of California San Diego

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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