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Atlas 14 estimates superseded those published in:
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)
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.
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
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2023/09/Screenshot-2023-09-05-at-3.14.21-PM.png?fit=1686%2C846&ssl=18461686adminadmin2023-09-05 16:12:162023-09-05 16:12:17Here Come New Precipitation-Frequency Estimates…Again
It’s easy to forget flooding in the middle of a drought. But we should never forget that Texas ranks #2 in states with the most flood damage. This and other statistics below demonstrate why we shouldn’t become complacent.
Debris pile from Imelda flood in Elm Grove Village (Kingwood).
Different Measures, Similar Rankings
Many ways exist to rank flood-prone areas and Texas ranks high on most of them.
Most hurricanes? Out of the 300 hurricanes that made landfall in the US since 1851, Texas ranks #2 after Florida with 66 hitting the Lone Star state – 22% of the U.S. total.
Percentage of state’s total population living in floodplains? Texas ties for 10th according to a 2017 study. But a 2023 TWDB study shows that 20% of Texans now live in floodplains; that would tie us for 3rd if nothing else changed.
Most disaster declarations? Texas ranks #2 when considering all types.
Flood deaths? Texas ranks #1. Two hundred people died between 2010 and 2022. Over a longer period of time, 1959-2014, the state had over 850 flood deaths.
As bad as the Texas statistics are, Harris County’s are even worse.
Between 1978 and 2021, Harris County led all counties in the the entire countryfor NFIP claims filed (171,300), about 44% of the total claims for all of Texas.
It’s important to look at many different measures, because no one measure conveys the full picture. For instance:
Number of hurricanes also reflects miles of subtropical shoreline.
The sheer size and population of Texas make it rank high on many measures. Said another way, we are a big target.
The high clay content of our soils discourages infiltration and encourages runoff of rainfall.
Dollar losses may depend as much as on affluence or population density in floodplains as the severity of flooding.
Dollar losses in Texas also reflect old building codes in many locations.
And then there’s the huge number of mobile homes in Texas. They are notoriously susceptible to high winds, like those often associated with hurricanes.
Their placement also makes them more vulnerable to flooding than other types of housing. A study by Headwaters Economics found that one in seven mobile homes is located in an area with high flood risk, compared to one in 10 for all other housing types.
Texas, a Leader in…
Texas leads the nation in many things: oil, gas, cotton, job creation, economic expansion and more. Unfortunately, we’re also a leader in flooding.
That’s enough to make a dent in the state’s budget, but not the problem. Perhaps we need to re-examine our priorities.
Posted by Bob Rehak on September 4, 2023, Labor Day
2197 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2019/09/Elm-Grove-9.19_71.jpg?fit=1500%2C1000&ssl=110001500adminadmin2023-09-04 17:02:452023-09-04 17:02:47Texas Ranks #2 in States with Most Flood Damage
When looking at buying property, your flood risk depends on at least ten factors. Unfortunately, people rarely consider most of them. Even if they do, they may not now how to assess them.
Harvey Flood. Photo by Sally Geis.
So, here’s a list of key factors that can increase or decrease your flood risk. I’ve also included examples and ways to explore their impact on your property or the property you’re considering buying:
Geography and Topography: The natural landscape of an area plays a significant role in its flood susceptibility. Flat, low-lying areas, river valleys, coastal regions, and areas near lakes or other bodies of water are more prone to flooding because water naturally collects in these locations. To investigate a particular area, check out resources such as the USGS National Map and FEMA’s National Flood Hazard Layer Viewer.
Proximity to Water Bodies: Areas near rivers, lakes, oceans, and other water bodies are at a higher risk of flooding. Riverine flooding, coastal flooding, and flash flooding can all occur in these regions. See any map or web sites such as RiskFactor.com.
Rainfall and Precipitation Patterns: Areas that receive heavy or prolonged rainfall are more likely to experience flooding. Rainfall can lead to flash floods, riverine flooding, and urban flooding when drainage systems are overwhelmed. In Texas, generally the farther east and closer to the coast you go, the more rainfall increases. To see the likelihood of precipitation in any given area, check out NOAA’s Atlas-14 site then investigate local infrastructure standards to see if they meet Atlas-14 standards or something less (prior). Also understand that NOAA is revising Atlas-14 already to incorporate impacts of climate change (see Atlas-15).
Climate and Weather Events: Areas prone to hurricanes, tropical storms, or other severe weather events are at risk of storm surges, heavy rainfall, and coastal flooding. Here are several sites that can help you find reliable climate data.
Human Development: Urbanization and land development can increase flood risk. Paved surfaces and buildings can reduce natural drainage and increase runoff, overwhelming drainage systems. Harris County has proposed minimum drainage standards for areas draining into Harris County, but not all surrounding areas have adopted these standards yet.
Deforestation and Land Use Changes: Changes in land use, such as deforestation or the construction of roads and buildings, can alter natural water flow patterns and increase flood risk. Think you’re protected? Unfortunately for homeowners, many wetlands are now being destroyed. The EPA and Army Corps amended the definition of protected “waters of the United States” in light of the decision in Sackett v. EPA in May. It narrowed the scope of the Clean Water Act and the EPA’s power to regulate waterways and wetlands.
Infrastructure and Drainage Systems: The condition and capacity of drainage systems, including stormwater sewers and levees, can affect an area’s flood vulnerability. Inadequate or poorly maintained infrastructure can lead to flooding. After Harvey, Harris County Flood Control embarked on an ambitious expansion of flood-mitigation infrastructure, but recently spending has fallen. More in some areas than others. So stay alert to what’s happening in your area.
Historical Flooding: Areas with a history of flooding are often at continued risk, as past floods can indicate a region’s susceptibility to future events. In Harris County, MAAPnext provides an excellent series of historical flood maps to help you understand your flood risk.
Land-Use Planning and Floodplain Management: Effective land-use planning, zoning regulations, and floodplain management can help mitigate flood risk by restricting construction in flood-prone areas and implementing flood control measures. There’s no zoning in Houston and little in surrounding areas. We do have floodplain management regulations. When purchasing property, always look upstream to see if those regulations are effectively enforced.
Few things affect a property’s value more dramatically than flooding.
Yet flood risk can change over time – for better or worse. So buyer beware. Or buyer be wet.
Posted by Bob Rehak on 9/3/2023 with some help from ChatGPT
2196 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.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2021/09/20170829-IMG_5756.jpg?fit=1200%2C800&ssl=18001200adminadmin2023-09-03 13:37:262023-09-03 13:39:18Factors that Affect Flood Risk and How to Assess Them
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:
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.
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:
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
Texas Ranks #2 in States with Most Flood Damage
It’s easy to forget flooding in the middle of a drought. But we should never forget that Texas ranks #2 in states with the most flood damage. This and other statistics below demonstrate why we shouldn’t become complacent.
Different Measures, Similar Rankings
Many ways exist to rank flood-prone areas and Texas ranks high on most of them.
Harris County Ranking
As bad as the Texas statistics are, Harris County’s are even worse.
Between 1978 and 2021, Harris County led all counties in the the entire country for NFIP claims filed (171,300), about 44% of the total claims for all of Texas.
Moreover, 42% of all Texans living in floodplains live in the San Jacinto watershed. The number of floodplain dwellers in the San Jacinto watershed alone exceeds the population of 15 states and the District of Columbia.
A Big Target
It’s important to look at many different measures, because no one measure conveys the full picture. For instance:
And then there’s the huge number of mobile homes in Texas. They are notoriously susceptible to high winds, like those often associated with hurricanes.
Their placement also makes them more vulnerable to flooding than other types of housing. A study by Headwaters Economics found that one in seven mobile homes is located in an area with high flood risk, compared to one in 10 for all other housing types.
Texas, a Leader in…
Texas leads the nation in many things: oil, gas, cotton, job creation, economic expansion and more. Unfortunately, we’re also a leader in flooding.
Better land-use and building codes could certainly help reduce the flooding. But will the state’s new flood plan recommend that? The focus seems to be on flood mitigation more than flood prevention.
The San Jacinto Regional Flood Planning Group recommended $46 billion worth of studies and mitigation projects in its regional plan. And the San Jacinto is just one of 15 watersheds in the state!
In sharp contrast to the magnitude of mitigation needs, the legislature voted only approximately $1 billion for flood prevention projects this year.
That’s enough to make a dent in the state’s budget, but not the problem. Perhaps we need to re-examine our priorities.
Posted by Bob Rehak on September 4, 2023, Labor Day
2197 Days since Hurricane Harvey
Factors that Affect Flood Risk and How to Assess Them
When looking at buying property, your flood risk depends on at least ten factors. Unfortunately, people rarely consider most of them. Even if they do, they may not now how to assess them.
So, here’s a list of key factors that can increase or decrease your flood risk. I’ve also included examples and ways to explore their impact on your property or the property you’re considering buying:
Few things affect a property’s value more dramatically than flooding.
Yet flood risk can change over time – for better or worse. So buyer beware. Or buyer be wet.
Posted by Bob Rehak on 9/3/2023 with some help from ChatGPT
2196 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.