[Ana] Oh, my gosh.

It survived the winter.

Yeah.

We moved here to this property in 1999.

And behind me, it's.

I'm very privileged and proud to have a little mini greenbelt.

That's what I call it.

[Reporter] Ana Aguirre has enjoyed the views along this Williamson Creek tributary since she moved here in 1999.

She didn't realize how quickly it could go from serene to surging.

[Ana] I did not realize I moved into an area that was flood prone.

But 98 was memorable.

2001 was memorable.

2013.

Catastrophic.

2015.

Catastrophic.

I mean, it seems like it happens almost every other year.

[Reporter] So why does it keep flooding in southeast Austin?

And what does it mean for the future of this neighborhood?

So why is there so much flooding in this part of town?

[Shunk] Our flood risk is citywide.

[Reporter] Kevin Shunk is the floodplain administrator for the city of Austin and he says this isn't a problem for just one community.

[Shunk] This area of central Texas is called flash flood alley because we have some world record rainfalls and we have some of the highest flood risk in the entire country, if not the world.

[Reporter] So all of Austin is at risk for flooding.

But there are also some key geographic differences between different parts of town that can change flood risks.

[Shunk] In west Austin, the creeks in that area, because it's a little hilly, are generally very channelized.

So the flood plains aren't as broad and wide because it doesn't it can stay within the channel, whereas in east Austin it's very flat.

So flood points tend to be very broad, very wide in that area.

[Reporter] Broad flat land can also be attractive places to build homes like those in the former lower Onion Creek community.

Despite the potential risks after deadly floods struck the community in 2013 and again in 2015, the city of Austin bought out the remaining homes.

That space is now the Onion Creek Metropolitan Park.

[Ana] When you have the lower Onion Creek community that was built in a floodplain, that should have never happened.

So that's why we should have regulations.

[Reporter] But regulations on things like impervious cover and where homes could be built haven't always kept pace with Austin's construction booms.

[Zoun] You can look at certain area and can tell that this was built after regulation versus this was built before regulation.

[Reporter] Reem Zoun is the director of the Flood Planning Division of the Texas Water Development Board, and she says it's not that developers were ignoring rules, it's just that the rules didn't exist yet.

[Zoun] And we saw a significant difference between like pre-drainage criteria, manual post drainage criteria manual.

There is no criteria.

So people did not need to adhere to anything.

[Reporter] Some of the earliest floodplain maps were created after Congress passed the National Flood Insurance Program in 1968.

To qualify for the program, local governments had to craft their own land use and flood mitigation rules.

Austin regulations went into effect in 1983, but many of the homes in southeast Austin, including Aguirre's, were built in the seventies.

Today, Shunk says there are lots of regulations regarding flooding and development.

[Shunk] Development can't cause adverse flooding in other properties, and they have to prove that before they can get a permit to build their development.

So that's one thing the city does, is to ensure that all of this development that is happening isn't going to cause more flooding on somebody else.

[Reporter] But creek overflow is just one of the flooding hazards.

The second one may become the bigger and costlier problem.

[Ana] Austin has two issues.

We've got creek flooding.

We expect that.

But then there's also localized flooding.

The localized flooding is when the city doesn't have the sufficient infrastructure to address the runoff.

[Shunk] That's one thing we're really concerned about is this these very small, very intense rainfall storms that are very quick that may flood in a very small area, but not flood the entire creek area.

[Reporter] And Texas receives more rainfall than experts originally thought.

A new study of rainfall data called Atlas 14 showed that what we used to consider a 500 year flood plain is now a 100 year flood plain.

Zoun says the state's current drainage infrastructure isn't large enough to handle Texas storms.

[Zoun] So they're kind of that twofold implication on it.

Your floodplain got larger because water needs more space to flow and then our infrastructure needs to be a little larger to handle this like a storm event.

They identified over 600 projects and the price tag of that is approximately $48 billion, 48 billion with a B, and this does not include all of the need in the state.

[Reporter] And some residents are concerned that larger storm events will now be the new normal because of climate change.

[Ana] We know we're getting much more rain and it's much more intense when it does happen.

And also part of it is manmade.

[Reporter] Many scientists see more rain in our future.

In a recent report, the state climatologist predicted urban flooding events could increase by 10 to 15% compared to the years 2000 to 2018.

Right.

Shunk and his team are currently working on updating the city's floodplain maps.

They expect them to be complete by 2025.

And Zoun's group is preparing a state flood plan to present to the legislature next year.

[Ana] So the blue is where you've got the fully developed 100 year flood plain.

[Reporter] In the meantime, Aguirre is encouraging her neighbors to get flood insurance and continues to push developers and city officials to be mindful of new construction projects.

[Ana] It's important to take care of the pieces that you cannot see.

That's what's underground, and that's the foundation.

It's kind of like building a home.

If you don't have a solid foundation, then what's above it is going to be compromised.