1000 year floods? Let’s get real

courtesy climate.gov

Five years ago today, we were suffering the stunning realization that Hurricane Harvey had dumped 30-50″ of rain on southeast Texas--in fact, an area of flooding happened that would cover the entire state of New Jersey. Nine Trillion gallons of water fell from that storm and while I called it “Biblical” proportions, we know that storm easily made the list of 1,000 year floods. In fact, consulting group MetStat declared Harvey to be a one in 500,000 years flood event. That’s right, the odds of a Harvey are twice in one million years, according to their research. And you were here for it. But given the odds of you even being you, alive and existing as the person you are, are one in 400 Trillion, this starts to make some sense, doesn’t it?

But let’s look a little closer at just what a 1000 year flood event means:

1000 year flood event

Oh great, so we’re going to have even more of them. But consider the Mississippi floods last Wednesday, the Dallas floods last Sunday night and these other thousand year floods that occurred in just the last month. That’s right, the past 30 days:

That's a lot of thousand year events for one summer

The cover shot photo is of Ellicott City, Maryland which flooded last June again--after having a thousand year flood in 2016 and another one in 2018.

And the definition of any flood is not about how much rain falls, but how much rain falls compared to normal and how much flooding happens to a particular place--Houston can handle five inches of rain, whereas Las Vegas’ annual rainfall is just under that much. If you look, there are ten inch rains often over the oceans where no one is affected. Likewise, we don’t have “two inch” floods, but the desert does! So it’s all relative.

Back to this thousand year flood thing that is happening all the time. In the 1960s, the government came up with flood insurance and had to figure out who needed it and, therefore, who would be paying for it. Extrapolating backward in time they came up with flood plains of 100 and 500 years even though we hardly have good data for even those first hundred. Sure, if you live by a river then your flood chances increase, but my parents lived on a big hill and in the right rain storm the gutters couldn’t handle the overflow and so the water flooded their basement. And hurricane horizontal-driven rain can easily flood a high rise through those balcony doors. Going UP is no guarantee you won’t flood.

So trying to determine who will flood and how often seems to be a pointless exercise. We can all flood under the right circumstances. Many of the original federal flood czars knew this and have been saying from the beginning that floods don’t happen to a person, they happen to a community and everyone is affected. Therefore, everyone should share the financial burden and responsibility. So if you see big changes in your flood insurance policy over the next years, costs either increasing or decreasing, that is why--we all have to pay a fair share to help flood victims regardless of whether we ever are one or not.

On that note, my thoughts are with those who truly suffered the worst wrath of Harvey back on this day five years ago. Do something relaxing and nice for yourself this weekend. You deserve it.


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About the Author:

KPRC 2's chief meteorologist with four decades of experience forecasting Houston's weather.