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.