By accident, I stumbled across some powerful historical flood loss visualization tools on Harris County Flood Control’s MAAPnext site today. They can help you understand the capricious nature of storms as well as political claims about which neighborhoods flood the most.
In 2019, using two FEMA grants and Flood Bond money, Harris County Flood Control District launched its MAAPnext project. MAAP stands for Modeling, Assessment and Awareness. The goal: to use new methodologies and technologies to improve understanding of flood risks throughout Harris County. The project goes far beyond updating Flood Insurance Rate Maps in the wake of recent storms. It also includes:
- Interactive historical flood loss visualization tools
- Water surface elevation change grids (maps showing difference between effective and revised floodplains)
- Flood depth grids (for various flood frequencies including 10%, 4%, 2%, 1% and 0.2% annual chance events)
- Urban flood maps (street flooding caused by rainfall exceeding storm sewer capacity)
- Percent annual chance grids (giving you your exact probability of being flooded within a mapped floodplain)
- 30-Year chance grids (showing your home’s exact chance of flooding within the life of a 30-year mortgage)
- Water surface elevation grids (showing the water surface elevation in various flood frequencies)
Not all of these maps have been released yet. For instance, MAAPnext/FEMA will release new preliminary flood insurance rate maps for public comment this fall. However, I did find three fascinating interactive maps showing the history of flood losses in Harris County.
Historical Flood Loss Tools
Cumulative Losses since 1978
The first map provides a visual representation of where all flooding claims have occurred throughout the county since 1978. A property’s flood risk can be a influenced by many factors but it’s important to remember that it can flood anywhere in Harris County. The darkest areas have the most cumulative flood losses. The lightest areas have the least.
To understand exactly WHERE and WHEN these flood losses happened, you need to go to the next two series of maps.
Historical Inundation Map
The Historical Inundation Map shows the extent of flooding in five different major storms since 2015. These include only streams with gages, not all Harris County channels. Zoom and scroll into an area of interest and then select the storm of interest from the layer menu.
You can toggle layers rapidly to see how floods compared to each other.
Flood-Loss History by Event
The map above shows the spread of flood waters in various events. However, to see the relative damage in census tracts, you need to go to the map called “Flood Loss History by Event.” Again, you’ll need to toggle layers to select the event of interest. The darker the colors, the more damage.
Tax Day 2016 Storm Damage
Hurricane Harvey 2017 Damage
Imelda 2019 Damage
For More Interactive Exploration…
Media accounts of major storms might lead you to believe that major storms affect all parts of the county equally. But they don’t. Who floods depends on upstream rainfall totals, dam releases, proximity to floodplains, development regulations, elevation above the flood plain and more.
The most interesting aspect of MAAPnext is that it will eventually incorporate all of these factors and give you an individual risk rating for your property or one that you are considering buying.
If knowledge is power, this is power cubed, because it let’s you look at flood risk in multiple dimensions.
I can’t wait until the project is fully finished. Check back often and click around this site as new features seem to be bolted on periodically. The bolted-on comment relates to my only complaint. All information (and there’s a lot of it) is grouped under five pages in ways that are rarely intuitive and often invisible from the highest levels. For instance, to get to the historical flood loss maps, you have to:
- Click on the home page
- Click on a link embedded in one of the visuals called “Flooding is Our #1 Disaster.”
- It will take you to a page called (strangely enough) “Understand Your Flood Risk.”
- Scroll down past 7 other topics to the bottom of page to find the interactive maps.
Presumably, helping people understand their flood risk is the most important objective of this site, but the page by that name appears nowhere in navigation. That said, have fun exploring. You’ll find many other hidden gems on this site.
And remember that all flood insurance policies renewing on or after April 1, 2022, will be subject to FEMA’s new Risk Rating 2.0 methodology.
Posted by Bob Rehak on 3/12/2022
1656 Days since Hurricane Harvey