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DROUGHT: The Importance of Drought Indicators

Image of Mississippi River on December 5, 2012

Mississippi River on December 5, 2012
Credit: U.S. Army Corps of Engineers, Team St. Louis

Drought can cause devastating impacts on the environment and on society, such as the near shutdown of Mississippi River barge traffic in 2012. These impacts make understanding and monitoring drought extremely important. Establishing the presence of drought is both a science and an art. Scientists look at both quantitative indices and at drought indicators to obtain a broad perspective of moisture deficiency over a region. They then combine this information with “on-the-ground” reports of drought impacts to fully characterize a given area’s drought condition.

A “drought indicator” is a way to look at one or more variables, such as precipitation, to describe available water in soil or hydrologic systems. It may be a record of a single measurement, such as rainfall at a particular rain gauge or it may be a complex index. Drought indicators enable scientists to describe drought in a consistent way across different times and places. However, these climate-based drought indicators do not reflect changes in how drought affects us. Increasing population density or intensive cultivation may worsen the effects of drought, making combining information important to view the full drought picture.

Indicators can come in many forms such as vegetation stress levels, agricultural productivity, incidents of wildfire, lake levels, precipitation amounts, snowpack, streamflow, and more. All of these can indicate the emergence, exacerbation, or improvement of drought conditions.

As the authority on drought in the United States, the U.S. Drought Monitor looks at information from all of these drought indicators in combination with a variety of other evidence when preparing its weekly report. Drought indicators are highly valuable in the creation of this report because they point to deficiencies and improvements, which serve to create the sentences that stitch the story together.

You can see the tools used by USDM at

This is part of a series of articles about monitoring and assessing drought conditions across the United States. Check back next week to learn more about how the degrees of drought reveal the whole picture or check out the weekly drill behind the U.S. Drought Monitor.