Tag Archive for: Washington Post

Flood Map Accuracy

On December 6, 2022, The Washington Post ran an article titled “America Underwater: Extreme floods expose the flaws in FEMA’s risk maps.” The lengthy story by Samuel Oakford, John Muyskens, Sarah Cahlan and Joyce Sohyun Lee cross-referenced photos and videos with FEMA flood maps from areas around the country that flooded last summer.

The basic premise: FEMA’s flood maps “are failing to warn Americans about flood risk.” The authors then claim, “The resulting picture leaves homeowners, prospective buyers, renters and cities in the dark about the potential dangers they face, which insurance they should buy and what kinds of development should be restricted.”

There’s certainly room for improvement in FEMA flood maps.

FEMA Map from National Flood Hazard Layer Viewer. Note how mapping stops at Montgomery County line, one of the issues cited in The Post article.

But is Climate Change the Reason for Inaccuracy?

However, the authors blame climate change for the inaccuracy far more than other contributing factors which are far more obvious.

FEMA is supposed to update flood maps every 5-10 years. It’s hard to imagine climate change invalidating them in that time period.

Climate is an average of weather occurring over much longer time periods. Depending on whether you talk to a meteorologist or a geologist, the time period could range from 30 to millions of years.

At least five major ice ages have occurred throughout Earth’s history: the earliest was over 2 billion years ago, and the most recent one began approximately 3 million years ago and continues today (yes, we live in an ice age!). Currently, we are in a warm interglacial that began about 11,000 years ago. The last period of glaciation, often called the “Ice Age,” peaked about 20,000 years ago. At that time, the world was on average probably about 10°F colder than today.

Interestingly, one day after The Post article, the New York Times ran a story about the DNA of animals found frozen in the permafrost of northern Greenland, just a few hundred miles from the North Pole. The 135 different species scientists found there paint a picture of an arctic once lush with life typical of warmer climates today.

But another thing puzzles me. I see climate change often mentioned as the reason for drought. The US Geological Survey states, “Climate change has further altered the natural pattern of droughts, making them more frequent, longer, and more severe.” But The Post uses almost identical language to blame climate change for frequent flooding in many of the same general areas at the same time. Which is it?

And to what degree can climate change explain flood map inaccuracy? Many more obvious reasons exist that are less of a stretch for any inaccuracies.

Reasons Listed in Post Article for Inaccuracy of Maps

Here’s a list of the references in The Washington Post story used to explain inaccuracies found within FEMA maps. I’ve broken them into two groups so you can see the weight they gave to climate change.

Climate-Change References:
  1. “As climate change accelerates, it is increasing types of flooding that the maps aren’t built to include.”
  2. “Extreme precipitation events are growing increasingly common.”
  3. “A warming climate allows storms to carry more moisture, producing greater rain or snow in a short period of time.”
  4. “Climate has changed so much that the maps aren’t going to keep up.”
  5. Maps are out of date, some decades-old “in a changing climate.”
  6. “The effects of a changing climate.”
  7. Climate change impacts are getting worse.
  8. Climate change is “pushing FEMA’s maps beyond their limits.”
  9.  A gap exists between the data that goes into FEMA maps and current climate conditions.
  10. Climate change baseline is changing.
  11. “Climate change velocities are high.”
  12. “Maps do not take climate change into account.”
  13. “Overestimating the rarity of some events even before climate change…”
Other Possible Explanations Mentioned by The Post:
  1. “Communities may resist expanding designated flood zones because it adds costs and can hamper development.”
  2. Not all areas that flooded are mapped yet.
  3.  “Local communities often resist the expansion of federal flood zones”
  4. “Maps do not forecast flooding. Maps only reflect past flooding…”
  5. “Local governments have been opposed to any maps that show an increasing risk.”
  6. Relatively high imperviousness of gentrifying areas.
  7. Maps don’t reflect intense bursts of rainfall in a short period and the resulting street flooding.
  8. Impervious surface is replacing porous surface.
  9. Maps cover mainly coastal and riverine flooding.
  10. “Rain combining with melted snowpack.”
  11. FEMA flood maps don’t even attempt to model urban flooding
  12. “City neglected drainage problems.”
  13. Local opposition to expanding the floodplain.
  14. No sense of urgency to update maps.
  15. “Multiple compounding factors contribute to the flooding”

However, the article makes no mention of the mathematical limitations of Extreme Value Analysis, the key to understanding the uncertainties associated with rainfall probabilities.

Floods Can Also Be Explained Without Climate Change

The second group of references in The Post article seems far more immediate, compelling and easily provable when explaining any inaccuracy found in flood maps. They’re certainly typical of what I have found in the Houston area.

For the past five years I have been researching instances of flooding in and around Harris County. I published more than 250 articles on different aspects of the 2019 Elm Grove floods alone. And I don’t recall one person ever blaming those on climate change.

Elm Grove did not flood during Harvey, but did flood on two much smaller rains in 2019. The difference? Clearcutting and insufficiently mitigated upstream development. Contractors clearcut approximately 270 acres immediately north of Elm Grove without building sufficient detention capacity before the rains fell.

Similar stories – with variations – have played out over and over again throughout the Houston region. For instance, we see developers filling in wetlands. Exaggerating the infiltration rates of soils. Underestimating impermeable cover. Building in floodplains. Building to outdated codes and floodplain regulations. Being grandfathered under old regulations. Various jurisdictions refusing to update regulations. And more.

Regardless of your position on climate change, this discussion dramatizes the needs to:

  • Understand your local flood risk and the factors that affect it
  • Buy flood insurance.

Hopefully, Harris County Flood Control District’s MAAPnext project will address data deficiencies discussed in The Post article. But it will be years before those maps become official. And when they do, the landscape will have already changed.

Posted by Bob Rehak on 12/12/22

1931 Days since Hurricane Harvey

The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.

‘Wind Fingerprints’: Scientists Dissect What Accounts for the Destructiveness of Different Storms

Last week, a story about ‘wind fingerprints’ in The Washington Post caught my eye. It purported to show the difference between Ida and Katrina. The story by Bonnie Berkowitz and Laris Karklis starts with this teaser: “Ida hit Louisiana with faster winds than Katrina, but a hurricane’s category number is just part of what makes each storm unique — and uniquely destructive.” I was hooked.

Factors in Fingerprinting Storms

“Ida struck Louisiana on Aug. 29 as a strong Category 4 on the Saffir-Simpson scale, with maximum winds of about 150 mph — much higher than the maximum winds of 125 mph from Katrina, a Category 3,” say the authors.

However, the wind speed is just part of the picture. To get the big picture, one must also consider:

  • Breadth of the wind field
  • Wind direction
  • Total energy contained in the storm
  • Forward motion
  • Angle at which it struck the coastline
  • Track
  • Proximity to population centers
  • And more.

The story quotes Michael Kozar, a meteorologist who models storms for risk-analysis company RMS. Says Kozar, each wind field is like a fingerprint.

“Each wind fingerprint is unique to the storm, and it is why each storm produces a unique amount of loss and has unique impacts.”

Michael Kozar, RMS

Examples of Wind Fingerprint Differences

“A very large storm with moderate winds may contain more integrated kinetic energy than an intense but small storm, and it may create havoc for people on land in a different way,” says the story.

The story goes into great detail comparing Ida to Katrina. Ida packed higher winds (150 vs. 125 mph peaks). But Katrina packed more energy – 116 terajoules vs. 47 for Ida. By comparison, Superstorm Sandy in 2012 had an estimated 330 terajoules of energy.

A terajoule is so large, it’s hard to find an analogy that puts it in perspective for most people. But scientists estimate that the atomic bomb over Hiroshima released about 63 terajoules of energy – slightly more than Ida, but a little less than half of Katrina.

RMS estimates the smaller punch of Ida was due in part to the shorter time it was able to gather steam, so to speak, over open water. Ida gained full strength just hours before landfall. But Katrina churned over the open Gulf for three days before slamming into Louisiana. It grew much larger, in fact, about twice as large.

Relative size of wind fields estimated by risk-analysis firm RMS. Katrina more than doubled Ida’s diameter.

RMS also explained how Katrina came in east of Lake Pontchartrain, while Ida came in to the west. With the counter-clockwise rotation of low pressure systems in the northern hemisphere, that meant Katrina pushed water toward New Orleans and Ida pushed water away.

The forward speed of a storm can make a huge difference in the types of damage it causes compared to its rotational speed. Category 4 Harvey, for instance, stalled over Houston for days, dropping torrential rains. But Category 5 Hurricane Andrew ripped through south Florida in hours. Harvey flooded homes. Andrew tore them apart.

This article gives you both insights and food for thought that can help you prepare better for the next storm. It’s highly recommended reading.

Posted by Bob Rehak on 9/7/2021 based on a story by Bonnie Berkowitz and Laris Karklis in The Washington Post and data from RMS

1470 Days since Hurricane Harvey

How a Hurricane Shaped World History

Bob Henson, a meteorologist and journalist based in Boulder, Colorado, published a fascinating a story in The Washington Post on September 26, 2020. It makes good weekend reading. The story is about a 17-year old boy named Alexander Hamilton, living on the island of St. Croix, when a hurricane struck it on August 31, 1772.

Alexander Hamilton, Portrait by John Trumbull

Hurricane Article Establishes Hamilton’s Creds as Writer

Says Henson, “The hurricane — probably at least a Category 3 in St. Croix, according to a leading weather historian — prompted a teenage Alexander Hamilton to write an evocative description of the storm published in a local newspaper. Impressed by his essay, leaders of the Caribbean island took up a collection to send him to the American Colonies for formal education. The rest is history…”

Hamilton literally wrote his way off the island.

Bob Henson in The Washington Post

Hamilton’s Account of the Storm

Hamilton wrote: “It seemed as if a total dissolution of nature was taking place. The roaring of the sea and wind, fiery meteors flying about it in the air, the prodigious glare of almost perpetual lightning, the crash of the falling houses, and the ear-piercing shrieks of the distressed, were sufficient to strike astonishment into Angels. A great part of the buildings throughout the Island are levelled to the ground, almost all the rest very much shattered; several persons killed and numbers utterly ruined; whole families running about the streets, unknowing where to find a place of shelter; the sick exposed to the keeness of water and air without a bed to lie upon, or a dry covering to their bodies; and our harbours entirely bare. In a word, misery, in all its most hideous shapes, spread over the whole face of the country.”

Busiest Hurricane Season in History

Michael Chenoweth, a climate historian quoted in the article, believes that the storm grew into a Category 4 hurricane and may have been one of the five strongest hurricanes in the Atlantic before 1900. Chenoweth also believes that the decade of that storm ties for the busiest in history.

Reading Henson’s article I felt compelled to dig more into the history of Hamilton and St. Croix.

History of St. Croix

St. Croix has been a territory of the United States since 1917. Columbus discovered the island in 1493, but the Spanish never colonized the island. Denmark, England, Norway and France jostled for possession of the island in the 1600s. For nearly 200 years, Saint Croix, St. Thomas and St. John were known as the Danish West Indies. In 1916, Denmark sold Saint Croix, St. Thomas, and St. John to the United States in the Treaty of the Danish West Indies. The cost: US$25 million in gold.

 Hamilton’s Contributions

Hamilton’s ideas are credited with laying the foundation for American government and finance.  He was:

  • An American statesman, politician, legal scholar, military commander, lawyer, banker, and economist.
  • One of the Founding Fathers of the United States.
  • New York’s delegate to the Constitutional Congress.
  • Our first Secretary of the Treasury.
  • Founder of the nation’s financial system.
  • An influential interpreter and promoter of the U.S. Constitution.
  • Commanding General of the US Army
  • Active in ending the legality of the international slave trade

Reshaping History

Hamilton campaigned against Aaron Burr, whom he felt was unprincipled. Hamilton died in a duel with Burr in New Jersey in 1804, but not before shaping the nation that would shape world history.

Had it not been for that hurricane in 1772, he might have died an orphan on St. Croix. And who knows how different history might have been?

Posted by Bob Rehak on 9/27/2020

1125 Days since Hurricane Harvey