U.S. Drought Monitor
A weekly drought monitor is produced jointly by the National Oceanic and Atmospheric Administration, the U.S. Department of Agriculture, and the National Drought Mitigation Center at the University of Nebraska-Lincoln. The map uses measurements of climatic, hydrologic and soil conditions, and reported impacts at locations around the United States.
U.S. Seasonal Drought Outlook
The National Weather Service (NOAA) produces a monthly U.S. Seasonal Drought Outlook that uses extended weather forecasts to predict whether an existing drought is likely to persist, remain but improve, or subside. It also projects locations where drought development is likely.
Hydrological Drought Monitor
The U.S. Geological Survey monitors hydrological drought conditions through WaterWatch and GroundwaterWatch. WaterWatch monitors streamflow levels in real time and compares them to their historical averages at specific locations, and groundwater watch does the same for ground water levels.
Surface and groundwater levels can change quickly from local weather events, even with a small amount of rainfall. Resultantly, they can be misleading. WaterWatch produces a daily drought map that compares 7-day average streamflow to historical streamflow averages on the same date across Maine. Note this map defines hydrological drought.
Drought is ultimately caused by precipitation deficits, which are all relative to the typical amount of rain/snowfall in a region. The High Plains Regional Climate Center (HPRCC) produces climate maps with support of the National Oceanic and Atmospheric Administration (NOAA) and the National Centers for Environmental Information (NCEI) that display how recent precipitation amounts compare to long term averages across the United States. The time scale of recent precipitation levels can range from 30 days to two years.
Agricultural affects from drought are noticed after signs of meteorological and hydrological drought are observed. The Palmer Drought Severity Index (PDSI) is one of the oldest tools used to measure drought and was developed primarily for agricultural purposes. The PDSI uses temperature and precipitation data to estimate relative dryness. Monthly PDSI values capture long term trends and not data on time scales of less than 12 months.