DROUGHT: Products Used for Drought Monitoring

Map of Weekly Precipitation Anomalies across the United States for May 5, 2013 to May 11, 2013

The U.S. Drought Monitor (USDM) has emerged as a powerful and respected tool for characterizing drought in the United States. The USDM is well established as an authoritative instrument for drought assessment because of its timeliness with weekly releases, its multi-agency effort, and its professional development combining indices, indicators, and objective blends of data and impacts. Taken together, data and information from many different products contribute to the development of the USDM report each week. NCDC’s data and products are just one part of an intricate web of tools used to monitor and understand drought conditions and to put them in historical perspective.

NCDC provides and maintains a variety of weekly and monthly products used in drought assessment. NCDC’s weekly temperature anomaly (change from long-term average) map, average temperature for the week map, weekly precipitation anomaly map, precipitation for the week map, and weekly Palmer Drought Index all aid in determining where drought is occurring and how severe it is. Monthly products are also available including precipitation and temperature rankings. Graphs of these rankings are available on a month-by-month or year-to-date basis for individual U.S. states, regions, or for the contiguous United States—and historically back to 1895.

The scientists studying drought also have a variety of monthly Palmer drought indices available from NCDC at their disposal. The Palmer Z Index measures short-term drought on a monthly scale. The Palmer Drought Severity Index attempts to measure the duration and intensity of drought. The Palmer Hydrological Drought Index, a long-term drought index, was developed to quantify hydrological effects of drought. NCDC also provides a Standardized Precipitation Index for use in drought monitoring, which is different from the Palmer drought indices. It is a probability index that considers only precipitation, while Palmer's indices are water balance indices that consider water supply, demand, and loss.

Many products for drought monitoring are also available from other partners through the National Integrated Drought Information System, who aid in creating the USDM, including those listed on the Drought Monitoring Tools website. In addition to these tools, NCDC provides a monthly drought report as part of the monthly climate reports, which describe conditions across the country, as well as a variety of other temperature, precipitation, and drought data and products.

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 drought from a paleoclimate perspective or check out the how drought impacts to the economy, environment, and society are monitored.