Floods in Houston
I reflect a bit on flooding situation in Houston, based on my previous post yesterday. Turns out, I have been through a lot of these in the past 25 years that I have been living here. So my personal experience alone is fairly lengthy in human life time. So let us see how many 100 year and 500 years event happened that I personally have experienced in the last 25 years!
First the definition:
A 100-year flood is an extreme flood event that has a 1% chance (1 in 100) of happening or being exceeded in any given year. A 500-year flood is an even rarer, more severe event that has a 0.2% chance (1 in 500) of occurring or being exceeded in any given year.
Key point in the definition: a 100 year flood is a 1% chance of happening in a given year! It is a statistical probability based on an entire given database. Here it is FEMA's US national database.
PS: It doesn't mean that the 100 year flood happens once in 100 year!!
I intend to prove that with my personal experience in living in Houston, TX alone!
It is about annual Risk!
Resources and Maps
FEMA maintains a national database of floods. It does have a very user friendly interface where you can type any address in the US and get the official assessment of risk. This is a public database and all information is public.
https://msc.fema.gov/portal/home
If you live in the US, feel free to type your address, as this is national free database.
I will use a sample but real address to explain this process. The address is
12110 Green Willow Falls Dr, Tomball, TX, 77375, USA
Here is the official legend:
| Category | Zone(s) | Annual Flood Risk | Description | Map Appearance |
|---|---|---|---|---|
| High Risk (SFHA) | A, AE, A1–A30, AO, AH | ≥1% (1-in-100 year flood) | Inland areas subject to inundation from 100-year flood | Shaded blue |
| V, VE | ≥1% (coastal + wave hazard) | Coastal areas exposed to storm surge and wave action | Shaded blue | |
| Floodway | Highest within SFHA | River channels + adjacent land needed to carry floodwaters | Red diagonal hatching overlay | |
| Moderate Risk | B / Shaded X | 0.2% (1-in-500 year flood) | Between 100-year and 500-year floodplain | Shaded orange |
| Low Risk | C / Unshaded X | <0.2% | Minimal flood hazard areas outside 500-year floodplain | Clear / unshaded |
| Undetermined | D | Unknown | Possible flood risk, but no detailed analysis completed | Not specifically defined |
If you look at the map above, the red diagonal area is the 'floodway'; in this case the Willow Creek. The Blue area is the overbank spillway, or the 100-yr flood zone, meaning each year, there is 1% or higher chance of this area getting flooded per year. The Orange area is between 100-yr and 500-yr flood zone, meaning there is a 0.2% or higher chance of this area getting flooded per year. Here is a simplified version of the same legend.
| Color on FEMA Map | Risk Level | Should You Build? 🚧 | Simple Interpretation |
|---|---|---|---|
| 🔵 Blue | High Risk | ❌ No | Regular flooding likely (100-year flood zone or worse) |
| 🔴 Red Hatch | Extreme Risk | ❌ Absolutely Not | Floodway — water must flow here during floods |
| 🟠 Orange | Moderate Risk | ⚠️ Be Careful | Less frequent, but still real flood risk (500-year) |
| ⚪ Clear / None | Low Risk | ✅ Generally Safer | Minimal flood risk, but not zero |
| 🟡 Undefined | Unknown | ⚠️ Proceed with caution | Risk not studied — uncertainty is a risk itself |
A single case
Let us closely look at the address I mentioned earlier in Tomball, and I will show you certain strange thing which is common when a subdivision development happens.
First, you see the following:
- Hatched, and Blue area fairly close to the home in question
- The subdivision magically stays in the X-zone, orange and empty area (where this house is).
- X-zone does NOT require flood insurance!
Do you see something funny? Or understand what I am getting at. Yes, usually subdivision built a highly higher earthed ground when the houses are built, which makes the area slightly higher than the surrounding. But it sort of magically follows the subdivision boundary. Regardless, would you be buying a property here in the Orange or 200 ft from the blue, even if it is deemed OKAY by this FEMA map?
Tell you what, let me share the flooding experience.
Major Floods in Houston
Note: these are all floods that I have personal memories, and I can not reading old news articles and listing them. I clearly remember these major events where almost all of greater Houston experience 500-yr floods. Meaning, in majority of Houston all of the Orange in the map was covered in water in each of the instances! Well not exactly everywhere all the time, but in most places.
2001 – Tropical Storm Allison
2005 – Hurricane Rita (evacuation crisis)
2008 – Hurricane Ike
2015 – Memorial Day Flood
2016 – Tax Day Flood + Memorial Day Flood
2017 – Hurricane Harvey
2019 – Tropical Storm Imelda
2020 – Beta
2021 – Nicholas
2024 – Hurricane Beryl
I count 11 event in the last 25 years. Among which 7 have been absolutely catastrophic! Now tell me how's that 500-year flood is working out for us? Let me list a few more details of those 7 events.
🟦 Tropical Storm Allison (June 2001)
- Dumped 30–40+ inches of rain over several days
- Flooded the Texas Medical Center, causing billions in damage
- ~70,000+ homes damaged, major infrastructure failure
- ~$5B in losses and dozens of fatalities
🟦 Hurricane Ike (September 2008)
- Massive storm surge along the coast
- Widespread power outages across Houston region
- One of the costliest hurricanes in Texas history
🟧 Memorial Day Flood (May 2015)
- ~12 inches of rain in ~10 hours
- Several fatalities and widespread street/home flooding
🟧 Tax Day Flood (April 2016)
- 12–16 inches in ~12 hours, with intense rainfall rates
- 10,000+ homes flooded
- Reservoirs hit record levels
🟧 Memorial Day Flood (May 2016)
- Occurred just weeks after Tax Day flood
- Re-flooded already saturated watersheds [hcfcd.org]
🟥 Hurricane Harvey (August 2017)
- Stalled over Houston for 4–5 days
- Dropped 30–50+ inches of rain (U.S. record-scale event)
- Flooded ~100,000 homes in Houston alone
- $125 + billion damage in Texas
One side note here: 30% of Houston homes had some kind of roof damage. It was in fact so severe, that after 2 years you can still see the Blue tarp on the roofs of the house, as the roofing and insurance industry had massive back logs!
🟨 Tropical Storm Imelda (September 2019)
- Some areas got 40+ inches
- Severe flooding east/northeast of Houston
So, I hope I can state where we live matters a lot and risks of flood changes accordingly. It is proven that rain storms, Hurricane and flooding are getting more severe every year and will continue to do so as the oceans progressively warm up due to Human Induced Climate Change.
When thinking about where to build or rent in flood-prone regions like Houston, FEMA map colors offer a simple but powerful guide. Areas shaded in blue or marked with red hatching are the highest risk—these are places where flooding is expected regularly or where floodwaters must flow, making them unsuitable for development if you want to avoid damage. Orange zones may appear safer but still carry meaningful flood risk over time, especially during extreme storms, so they require caution. Only the clear or unshaded areas represent relatively lower risk, though even these are not completely flood-free. In short, the closer a property is to blue or red on the map, the more likely it is that water will eventually find its way there—and building decisions should reflect that reality.
Climate Change is absolutely the thing I'm most worried about, particularly floods, storms and frost that affects crop yields. I've never been involved in a flood, but I imagine it's absolutely terrifying when you don't know how quickly or by how much the water will rise. Governments truly need to be investing way more into adaption now, because obviously we can't keep rebuilding over and over again after fires, floods and storms.
Yes. Trouble is here in the US, under current administration, the opposite is happening. Govt., is taking all the money in different corruptions and all funding related to climate research is cut. It fact FEMA is barely surviving, they fired virtually everyone there.
I had to force myself to read this. I get nervous just thinking about it. That's why I bought flood insurance. We live on Long Island (NY). This is almost by definition a flood zone. According to one site 31.5% of all homes in my county are at high risk for flood. So, when we went to shop for a home a couple of years ago, one of the things we checked every single time we looked at a home was flood risk. There is always a flood risk, anywhere, but we were determined to get the lowest risk possible. There is a site, First Street.org https://help.firststreet.org/hc/en-us/articles/360047585694-How-is-my-Flood-Factor-calculated that offers an assessment of many environmental risks. In my area, I don't think FEMA has drawn a map since 2009, so that's not much help. Realtors cite First Street data to helps buyers assess a property.
According to First Street, my property has the lowest flood risk, but still there is risk and we get hurricanes all the time her. Hence the flood insurance. I need that to sleep at night :)
I am glad that you found a solution.
Ah, that makes sense that it is an annual chance. I never really dug into it enough to really learn about it, but I know my wife was asking me how can it be happening again if it only happens once in 100 years. :) How close to Houston was the one they just had that hit that girls camp? That was heartbreaking. Though having been through a couple floods, they are all heartbreaking in one way or another.
That event was around Texas Hill country. It was too close to home emotionally! The tragedy you were talking about happened morning of July 4th at Camp Mystic at the bank of Guadalupe River. My daughter went to a similar camp just the summer before, just a few miles down the river. There are numerous camps along the rivers ...
I shudder just to think about it unfortunately.
I can only imagine! How scary!
Since you mentioned
This is Camp Mystic in the same FEMA tool
Notice: The Camp was in fact just outside the Blue Zone. Also the event is not major hurricane or anything. Just a night of rain upstream.
Crazy. Not too hard to see how that little area could end up under water though.