Drought may be a term you have heard quite often, but the definition of a drought is rather complex. While most things are measured by the presence of something, like rainfall, snow or winds, drought is measuring the absence of something - water.

The National Weather Service defines drought as, “A deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizable area.”

But what can make measuring drought conditions challenging is that what might be a drought for one area, might be perfectly normal conditions for another. It widely varies from region to region - therefore, drought is very difficult to predict and monitor. In fact, according to drought.gov, in the early 1980s scientists found more than 150 different published definitions of drought - yikes!

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One of the most notable droughts in recent years was the California drought that lasted three years from 2020 through 2022. A series of atmospheric rivers began moving through in 2022 that eventually brought an end to drought conditions.

The U.S. drought monitor has four levels of drought - moderate, severe, extreme, exceptional. They release their findings every Thursday as an update on what the country is facing in terms of drought conditions.

While some droughts slowly creep up over time, there’s something called a “flash drought” that occurs when lack of rainfall, high temperatures and sunshine combine to result in a quick-developing drought.

This segment originally appeared in today's edition of the Morning Brief newsletter. Sign up here to get weekday updates from The Weather Channel and our meteorologists.

J​ennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.