Weatherz School: Drought

How do you know you’re in a drought? Can you tell based on a starved lawn, or a local stream that’s running low? Or maybe you know you’re in a drought because a map with blobs of brown says you are.

Drought is a normal part of the climate. It’s impacts aren’t felt as quickly as those from a tornado or a hurricane, but losses from a drought can be just as substantial. Drought can affect everything from wildfire risk to energy production.

A drought that hasn’t yet lasted for 6 months is considered short-term. This is when we see impacts on agriculture and grasslands, and the level of drought can change rapidly.

A drought lasting longer than 6 months is long-term. This has deeper impacts on the water system and ecosystem. The longer it lasts, the more rain you need for the drought category to change.

It’s important to keep track of the drought conditions. That’s why the U.S. Drought Monitor was created in 1999. It’s a team effort between the National Drought Mitigation Center (NDMC), the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Department of Agriculture (USDA).

These meteorologists and climatologists don’t just pay attention to how much it rained. They do look at precipitation, but also at streamflow, reservoir levels, temperature and evaporative demand, soil moisture and vegetation health. The Drought Monitor is a blend of all of these observations along with insight from a network of more than 450 experts.

The map is made by people, not computers. That’s why it takes two days for them to put each report together. Maps issued on Thursdays reflect data from 7 am CST for the previous Tuesday.

The map uses six classifications: normal conditions, abnormally dry (D0), showing areas that may be going into or are coming out of drought, and four levels of drought: moderate (D1), severe (D2), extreme (D3) and exceptional (D4).

So if you’ve wondered why care so much about those blobs of brown, that’s what the U.S. Drought Monitor is and why it matters.