Tag Archive for: Atlas 15

Here Come New Precipitation-Frequency Estimates…Again

NOAA’s new Atlas 15 precipitation-frequency estimates will soon replace recently introduced Atlas 14 estimates – even before the Atlas 14 estimates have been fully adopted and integrated into local regulations.

About Precipitation-Frequency Estimates

Engineers use precipitation-frequency estimates to design, plan and manage infrastructure under Federal, State and local regulations. For instance, to ensure homes are built X feet above the 100-year floodplain, engineers must “know” how much rain will fall in a 100-year storm. Predicting that is one of NOAA’s jobs.

However, haphazard adoption of the new estimates has created a patchwork quilt of regulations across Texas and the U.S. One of the dirty, little secrets in the flood mitigation business is that many jurisdictions fail to adopt the new estimates and update their regulations accordingly. It’s costly, time-consuming, and raises the bar for developers.

So, many jurisdictions continue to use lower estimates to help attract development.

But designing infrastructure around artificially low rainfall estimates can lead to insufficient mitigation that increases flood risk for everyone.

Some Estimates Now in Effect Go Back 60 Years

In 2018, NOAA introduced Atlas 14 precipitation-frequency estimates for Texas. They replaced earlier estimates published by NOAA as early as the 1960s. Some parts of the Houston region still use those earlier estimates today.

Atlas 14 estimates superseded those published in:

  1. Weather Bureau Technical Paper No. 40, Rainfall Frequency Atlas of the United States for Durations from 30 Minutes to 24 Hours and Return Periods from 1 to 100 Years (Hershfield, 1961)
  2. Weather Bureau Technical Paper No. 49, Two- to Ten-Day Precipitation for Return Periods of 2 to 100 Years in the Contiguous United States (Miller, 1964).

Newest Estimates Will Incorporate Climate Change

Compared to those, Atlas 14 estimates are more accurate. They incorporate data from newer technologies and more data collected over longer periods. Atlas 14 totals increased 30-40% for the Lake Houston Area.

The Atlas 15 estimates are just getting underway and have not yet been developed. NOAA expects to release them in 2027.

Atlas-15 timeline by NOAA

NOAA claims its Atlas-15 update will improve precipitation-frequency estimates by leveraging non-stationary climate estimates. Previous estimates, such as Atlas 14, have assumed a stationary climate.

In statistics, “non-stationary” means the underlying environment changes, say due to some strong trend or seasonality. Many people believe climate is changing and hence the desire to build that into the new precipitation-frequency estimates.

National Funding, New Updates Every 10 Years

Historically, NOAA precipitation-frequency estimates have been funded by states and other users, on a cost-reimbursable basis. However, that is changing.

Moving forward, the Federal government will fund precipitation-frequency updates. Under the Floods Act, signed into law in December 2022, NOAA will update precipitation-frequency estimates every 10 years.

Goals include:

  • Updating standards
  • Incorporating climate change
  • For the entire country.

Voluntary, Local Participation

But there’s a dirty little secret that not many people know about. Nothing forces individual cities, counties or states to adopt the estimates and work them into their regulations.

That’s a big job. And an expensive one. So, not all jurisdictions do it. Many areas surrounding Houston still plan infrastructure using data developed 60 years ago.

If you plan on less rain, channels can be narrower and stormwater-detention basins smaller. But residents are not protected as much as they should be.

Posted by Bob Rehak on 9/5/2023 based on information from NOAA.

2198 Days since Hurricane Harvey

New Data Suggests Houston’s Expected 100-Year Flood Is More Likely to Happen Every 8 to 23 Years

First Street Foundation, a non-profit risk-research group, estimates (based on what it says are “well known” Atlas-14 flaws) that a so-called 100-year flood event in Houston could likely happen every 8 to 23 years.

NOAA’s Atlas 14, a massive, years-long effort, which hasn’t even been fully implemented yet, may already be seriously out of date according to First Street.

As a result, First Street claims the design standards for infrastructure projects based on erroneous Atlas-14 data are likely to fail. Trillions of infrastructure investment dollars hang in the balance.

NOAA Replacing Atlas 14 with Atlas 15 Already

NOAA expects to release its latest Atlas-15 rainfall probability statistics for the U.S. sometime in 2027. Like Atlas 14 below, they will contain probabilities for every location in the country – for durations ranging from 5 minutes to 60 days and recurrence intervals from 1 year to 1000 years.

atlas 14 rainfall probabilities
Atlas 14 Probabilities for the North Houston area.

Moreover, for the first time ever, Atlas-15 probabilities will come in two flavors: with and without estimates for the impact of climate change.

First Street Foundation, a non-profit research and technology group, specializes in environmental risk assessment. They position their system, RiskFactor.com, as a stopgap until NOAA releases Atlas 15.

Time Lags Cause Confusion, Create Danger

FEMA still has not released flood maps based on the Atlas-14 probabilities above. The MAAPNext Group within Harris County Flood Control District has been working on those since Harvey. MAAPNext’s latest timeline (below) shows that FEMA may not make Atlas-14-based flood maps official for another 3+ years.

Engineers and government officials use this data when designing new subdivisions, industrial facilities, bridges, highways and other infrastructure.

For instance, they need to know, how high the bridge must be to let water flow under it during a flood to avoid catastrophes like the one below.

I-69 repairs
Old data led TxDoT to inadequately design the I-69 bridge over the San Jacinto West Fork. Repairs took more than a year after Harvey to complete while residents endured massive traffic jams.

Atlas 15 Underway Before Atlas 14 Implemented

A copyrighted article in the New York Times this morning by Raymond Zhong was titled “Intensifying Rains Pose Hidden Flood Risks Across the U.S.” In it, Mr. Zhong claims that new calculations show hazardous storms can dump significantly more water than previously believed.

“One in nine residents of the lower 48 states, largely in populous regions including the Mid-Atlantic and the Texas Gulf Coast, is at significant risk of downpours that deliver at least 50 percent more rain per hour than local pipes, channels and culverts might be designed to drain,” says Zhong.

Compounding the problem, “NOAA’s estimates are ‘the floor, not a ceiling,'” said Zhong, quoting Abdullah Hasan, a White House spokesman.

“That means millions of homeowners might be making decisions with an incomplete understanding of the true physical and financial risks they face,” said Zhong.

145,000 Houston Homes and Billions in Infrastructure Caught in Time Lag

Zhong quoted First Street Foundation, which said that in Houston alone, as many as 145,000 homes may be in the 100-year flood zone, but that they are not shown that way in current FEMA flood maps.

To put Atlas 15 and its climate change corrections into perspective…

First Street estimates that in Houston, what we currently think of as a 100-year flood may actually be an 8- to 23-year flood.

First Street Foundation Press Release

All this comes as the nation gears up to spend more than $1.2 trillion dollars on infrastructure which Congress and President Biden approved in 2021.

And that $1.2 trillion doesn’t even include the money homebuyers spend each year. About 30% of all household income in the U.S. goes toward housing. And the average American moves once every seven years.

That means virtually everyone is likely not making home-buying decisions based on the most current (accurate) flood probabilities. By the time FEMA releases Harvey-based Atlas-14 flood maps, Atlas-15 revisions will already be available to a select few.

While the Association of State Flood Plain Managers finds First Street data useful, it emailed a report at the close of business today about First Street. The report says that “ASFPM has and will continue to support NOAA’s work on Atlas 14 and 15, which will remain the gold standard within our profession.”

Problems Caused By Lack of Timely Updates

The vast majority of developers, homebuilders and engineers are ethical. But some less scrupulous developers can exploit confusion caused by irregular update policies.

Likewise, engineers who designed a bridge to one set of specs, may find their work out-dated before construction starts. What are the ethical obligations in a case like that?

Just this year, we’ve seen numerous instances of developers trying to get their plans grandfathered under pre-Atlas-14 regulations even as the U.S. moves toward Atlas 15. Little wonder that when a flood happens, few can explain where the system went wrong.

“The fact that the Nation will not have the most accurate estimates of extreme precipitation likelihoods available at the time of the design of these projects means that many of them will be out of date on the day they are opened to the public,” said Matthew Eby, Founder and Executive Director of First Street Foundation.

Governments at all levels need to work better together to shorten the data supply chain. Doing so could save Americans trillions of dollars.

Posted by Bob Rehak on 6/26/2023

2127 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.