After the scale of Harvey, do we need a new or better way to measure floods? AP Photo/David J. Phillip
Rescue boats fill Tidwell Rd. as they help flood victims evacuate as floodwaters from Tropical Storm Harvey rise Monday, Aug. 28, 2017, in Houston. (AP Photo/David J. Phillip)

Time and time again during the news coverage of Harvey, newscasters and experts discussed the concept of ‘100-year’ and ‘500-year’ and even ‘1,000-year’ flood events.

But, in the unprecedented aftermath of the storm, do these metrics mean anything any more?

For starters, the ‘100-year’ flood appears to be a vastly misunderstood concept; it does not mean, as the name would suggest, a flood only happens once in a hundred years.

The number actually refers to the chances of a flood of such magnitude occurring, meaning a 100-year flood is one with less than a one percent chance of happening in any given year.

Screen shot of

RELATED: Ellen DeGeneres Helps Boost Harvey Relief Donations to 8.5 Million

According to news website, the 100-year measurement isn’t just confusing – it skews people’s understanding of the statistical measurements behind flood prediction.

For context, Harvey is now being described as a 1,000-year flood event, meaning there was a one in 1,000 chance of it happening in any given year.

The 100-year measurement originated in 1973, when the 100-year floodplain was first evaluated by the government and regulations were enacted for the homes built inside its boundaries.

To come up with floodplain measurements, scientists today examine data about normal water flow, water depth and a host of other variables to determine when and where water will rise to dangerous levels.

But, even after these points are plotted on a map, they aren’t exact.

In Houston, for example, 30-40 percent of flood insurance claims are filed for property outside of the floodplain.

RELATED: Stars Aligned on GMA to Raise Money for Harvey Relief


Currently, scientists are faced with the problems of incomplete data compounded by an incomplete understanding of the effects of climate, and manmade, change on flood areas.

With some reported 30,000 households in the Houston area in need of help, if you are in need or would like to give back, read more here.

Stories You Might Like