What qualifies a flood to be labeled 100-year versus 1000-year events?

AUSTIN (KXAN) - Central Texas faced historic, catastrophic flooding this month, with some meteorologists calling these floods 1000-year rainfall events. What qualifies a flood to be labeled 100-year or 1000-year events?

Flood Terminology

This type of terminology is based on statistical probability. For example, a 100-year rainfall event doesn't mean the next big storm will be in 3025. A 100-year rainfall event means there is a 1% chance on any given year the total will be equal or higher in the given area.

There are different criteria to qualify as a 100-year or 1000-year rainfall event, such as statistical probability, rainfall amounts, duration of impact, and the environment.

Texas Events

This July, flash flooding claimed more than 100 lives, 37 of whom were children.

How to help local Texas communities impacted by flooding

In recent years, Hurricane Harvey created an estimated over $100 billion in damages, with several feet of rainfall measured.

The map below plots some recent 100 and 1000-year rainfall events that impacted the Lone Star State.