What does the Map Show? | National Drought Mitigation Center
National Drought Mitigation Center

What does the Map Show?

Drought Intensity Scale

The map has a great deal of information summarized on a single page. We’ll break down the map and look at the different features.

First, let’s take a closer look at the colors on the map. The categories include D0, abnormally dry conditions and 4 categories of drought intensity. D0 is not considered drought. Instead, it can be thought of as a drought watch or “heads up” to areas that may be entering drought or to indicate a location that is recovering from drought but not yet back to normal as impacts can linger. The drought categories range from D1 to D4, with D4 being the most severe. The white areas on the map are experiencing near‐normal to wet conditions.

Timescales of Impacts

Since “drought” means that there is a moisture deficit bad enough to have social, environmental or economic effects, we generally include a depiction of what the primary physical effects, called drought impacts, are.

The letter S on the map represents areas that are experiencing the types of impacts that we see with drought that has been present for 6 months or less. Examples of short‐term impacts include impacts to the environment, agriculture, and grasslands and include things such as slow crop growth and dry vegetation.

The letter L on the map represents areas that are experiencing the impacts that typically occur with long‐term drought or droughts which have a duration of 6 months or more. Examples of long‐term impacts may include low streamflow and groundwater, receding reservoir and lake levels, reductions in wetlands, and changes to wildlife habitats.

Notice that on this map some locations in the U.S. contain both an S and an L. This depiction typically represent areas that are experiencing or haven’t recovered from long‐term drought and are also experiencing short‐term impacts due to seasonal shortages in precipitation.

Finally, the drought map also uses heavy, black lines to delineate impact types between “connected” drought areas. For example, all impacts within the black lines are related to long‐term drought whereas the impacts outside of the heavy, black line are related to short‐term seasonal dryness and/or long‐term drought conditions.

Summary and Disclaimer

Each week, the author of the U.S. Drought Monitor provides a written summary and regional breakdown explaining the changes in the drought depiction on that week’s map.

The U.S. Drought Monitor contains a statement communicating that it focuses on broad‐scale conditions. Local conditions can, and do, vary. It just is not possible to represent local conditions on a national scale map. For information on local details and impacts, individuals should consult with their state climatologist or other local officials. Although it is based on many types of data, including observations from local experts across the country, we don’t recommend using it to infer specifics about local conditions. It can certainly be used to identify areas likely being impacted by drought, including areas experiencing water shortages. However, decision‐makers in many circumstances have successfully taken measures to reduce vulnerability to drought. Large urban water systems generally have diverse water supplies and can keep the water flowing in both dry and wet years. The U.S. Drought Monitor is in no way intended to replace assessments or guidance from local water systems or governing bodies as to whether or not residents should conserve water.

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