Overview of the U.S. Drought Monitor
The U.S. Drought Monitor is a weekly snapshot of drought conditions across the United States. The purpose of the map is to show people where drought is occurring, its spatial extent and severity, and the time scale of the associated impacts.
In the drought world we say that drought is defined by those that it impacts. For example, those in the agricultural sector will have a different view of what drought is than those who deal in water supply. The USDM captures multiple types of drought on a single map. These include:
Meteorological drought: Meteorological drought is determined by the lack of precipitation and how conditions such as temperature and winds affect the amount of moisture. It is expressed in relation to the average conditions for a region. Meteorological drought is region specific since precipitation is highly variable from region to region. For example, a location in Florida may receive more rainfall during a drought than a location in New Mexico receives during an entire year.
Agricultural drought: This type of drought links the characteristics of meteorological drought to agriculture or landscapes. Agricultural drought focuses on precipitation shortages, evaporative demand, and soil moisture deficits. This type of drought is also dependent upon plant type, stage of growth, and soil properties.
Hydrological drought: Hydrological drought is associated with the effects of rain and snow shortfalls on streamflow, reservoir and lake levels, and groundwater. Because it takes longer for precipitation deficiencies to show up in other components of the hydrological system, this type of drought can be out of phase with the other types of drought.
Ecological drought: This type of drought results from prolonged and widespread deficit in naturally available water supplies that create multiple stresses across ecosystems
Socio‐economic drought: Socio‐economic drought includes the impact of drought on the economy related to supply and demand. While people typically think of agricultural products, drought can also affect hydroelectric energy generation, ethanol production, and numerous other items. In addition, drought impacts tourism, public health, infrastructure, and many other components of society.
It’s also important to note what the U.S. Drought Monitor isn’t. The U.S. Drought Monitor is also not based solely on precipitation. The map analysis includes numerous indicators, drought impacts, and reports from over 400 expert observers around the country.
It is not a computer model. Each week, a real person analyzes numerous types of drought related data and draws the lines on the map based off the pervious week’s map.
The Drought Monitor is also not a forecast of future conditions. It is based on available data for current conditions.
Finally, the U.S. Drought Monitor is not a declaration of drought; declarations are made by federal, state, and local agencies which may, or may not, use the U.S. Drought Monitor to inform its decisions.