Texas is big. Everything is bigger here, including the rain. If you’ve ever lived through a spring in the Hill Country or a late summer on the Gulf Coast, you know that the sky doesn't just leak—it breaks. But when people ask what started the flood in texas, they usually aren't looking for a single date on a calendar. They want to know why the water rises so fast and why it stays so long.
It's a mix of bad luck, weird geography, and atmospheric physics that frankly doesn't care about your property lines.
Take 2017. Hurricane Harvey. That wasn't just a "storm." It was a geological event. Or look at the 2015 Memorial Day floods. People were swept away in Wimberley because a "wall of water" hit the Blanco River. It happens over and over. To understand the "what" and the "how," we have to look at the literal ground we stand on and the massive engines of the Gulf of Mexico.
The Gulf of Mexico: A Giant Heat Engine
Basically, the Gulf of Mexico is a warm, shallow bathtub. It’s the primary culprit for almost every major Texas deluge. When the water gets hot, it evaporates. That moisture has to go somewhere. Usually, a high-pressure system called the Bermuda High acts like a giant fan, blowing all that wet air straight into the Texas coastline.
This is where the trouble begins.
When you have that much moisture sitting over the state, all it takes is a "trigger" to turn it into liquid. Sometimes that trigger is a cold front coming down from the Rockies. Other times, it's a tropical wave. But the most dangerous scenario—the one that really answers the question of what started the flood in texas during the worst years—is atmospheric stalling.
In the case of Harvey, the steering currents just... quit. The storm sat there. It sucked up water from the Gulf, dumped it on Houston, and then looped back to grab more. It’s like a conveyor belt of rain that refuses to turn off. Meteorologists call this "training," where storms follow each other like boxcars on a train track, hitting the same spot for twelve hours straight.
Flash Flood Alley: Why Central Texas is a Target
You can't talk about Texas flooding without talking about the Balcones Escarpment. It's a fancy name for a line of cliffs and hills that runs from Del Rio up through Waco and Dallas. If you’re driving west on I-35, you’ve seen it.
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This ridge is a literal wall.
When moist air from the Gulf hits those hills, it's forced upward. This is called orographic lift. As the air rises, it cools. Cool air can't hold as much water as warm air, so the moisture falls out as rain. Fast. This makes Central Texas one of the most flash-flood-prone regions in the entire United States. They call it "Flash Flood Alley" for a reason.
The soil doesn't help.
Much of the Hill Country is limestone and thin clay. It’s basically rock. When it rains three inches in an hour, the ground doesn't soak it up. It acts like concrete. The water immediately runs into the creeks, then the rivers, and suddenly the Guadalupe or the Llano is rising twenty feet in an afternoon. That is exactly what started the flood in texas back in the legendary 1998 floods and again in 2015.
The Human Element: Concrete and Drainage
We have to be honest about the "pave over" effect. Texas is booming. Austin, Dallas, and Houston are expanding at a rate that is honestly hard to wrap your head around. Every time we build a new strip mall or a suburban cul-de-sac, we replace prairie grass with asphalt.
Grass is a sponge. Asphalt is a slide.
In Houston, the drainage system relies on bayous and massive detention ponds. But the city is famously flat. There’s nowhere for the water to go by gravity alone. During the 2016 "Tax Day" floods, the sheer volume of water overwhelmed the Addicks and Barker reservoirs. These were built in the 1940s. They were never meant to protect the amount of concrete that exists in Harris County today.
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Why the 2024 and 2025 Events Felt Different
Recently, we've seen a shift in how these floods start. It's not always a named hurricane. Sometimes it’s an "Upper Level Low"—a spinning pool of cold air high in the sky that gets cut off from the main jet stream. It just hovers.
In May 2024, Southeast Texas saw massive flooding because of these stalled systems. The ground was already saturated from a wet spring. When the ground is full, every single drop that falls becomes "runoff." That’s the tipping point. You can have a moderate rainstorm cause a catastrophic flood if the "antecedent moisture"—the wetness already in the soil—is high enough.
Climate Dynamics: El Niño vs. La Niña
You've probably heard weather folks talk about El Niño until they’re blue in the face. It matters. Generally, El Niño years bring a stronger sub-tropical jet stream across the southern U.S. This acts like a highway for storms.
However, some of our worst floods happen during the transition.
When we move from a dry La Niña (which causes droughts) into an El Niño, the Texas landscape is often brittle and baked hard. This "crust" makes the first few heavy rains even more dangerous because the parched earth acts like a waterproof shield, sending every drop of water straight into the nearest drainage ditch.
Misconceptions About Texas Flooding
One big mistake people make is thinking they are safe because they don't live near a river. In the 2017 events, a huge percentage of flooded homes were outside the "500-year floodplain."
How does that happen?
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It’s called "urban flooding." It’s when the rain falls so fast that the storm sewers literally can’t take it. The water backs up into the streets and eventually into living rooms. It doesn't matter if you're on a hill if the street in front of your house turns into a lake because the drain is clogged with debris or just too small for the volume.
Another myth is that "the dams will save us." Dams are tools, not magic wands. In many Texas floods, engineers are forced to do "controlled releases." If the dam gets too full, they have to let water out to prevent the entire structure from failing. This often floods the people downstream to save the people upstream. It’s a brutal math.
Breaking Down the "What Started It" Timeline
If we look at a typical major Texas flood event, the timeline usually looks like this:
- Saturating the Sponge: A week of light to moderate rain that fills the soil and the local creeks.
- The Trigger: A stalled frontal boundary or a tropical disturbance moves in.
- The Engine: High-octane moisture from the Gulf feeds into the storm.
- The Geography: The hills of the Balcones Escarpment or the flat coastal plains prevent the water from moving away quickly.
- The Infrastructure Gap: The volume of water exceeds the design capacity of 20th-century drainage systems.
What You Can Actually Do
Knowing what started the flood in texas is the first step, but surviving the next one is about action. Most people wait until the rain starts to think about flood insurance. That’s a mistake. There is usually a 30-day waiting period for NFIP (National Flood Insurance Program) policies to kick in.
If you live in Texas, you are in a flood zone. Some parts are just higher risk than others.
Check your local "Flood Education Mapping Tool." Don't just look at the 100-year line. Look at the topography. If your house is at the bottom of a cul-de-sac, you’re at risk for urban flooding regardless of what the federal maps say.
Practical Steps for Homeowners
- Clean your gutters every season. It sounds small, but if water can't get off your roof and away from your foundation, it’s going into your crawlspace.
- Install a backflow valve. In many Texas cities, floodwater causes sewage to back up into homes. A simple valve can prevent a disgusting (and expensive) mess.
- Grade your yard. Make sure the soil slopes away from your house. Over time, Texas soil shifts and settles, often creating "bowls" against the foundation that trap water.
- Have a "Go Bag" that isn't just for hurricanes. Flash floods happen at 3:00 AM with zero warning. You need your documents, meds, and a way to charge your phone in a waterproof bag ready to grab.
Texas weather is beautiful, but it’s volatile. The floods are a natural part of the ecosystem—the landscape was literally shaped by them over millions of years. We’re just the ones living in the way. Understanding that the "start" of a flood is a combination of Gulf heat, rocky hills, and old infrastructure helps you respect the power of the water when the sky finally turns that bruised purple color.
Next Steps for Safety and Awareness
- Verify your flood risk: Visit the FEMA Flood Map Service Center and enter your specific address. Do not rely on general neighborhood rumors.
- Audit your insurance: Call your agent today to see if a private flood policy or an NFIP policy is right for you. Remember the 30-day rule.
- Monitor "Turn Around Don't Drown" zones: Familiarize yourself with the low-water crossings on your daily commute. In Texas, the majority of flood deaths occur in vehicles. If there is water over the road, there is no way to know if the road underneath is still there.
- Install a weather app with localized alerts: Use something like Baron Critical Weather or the standard NOAA alerts to get "Flash Flood Warnings" pushed to your phone with sound, even when you're sleeping.