A US Drought Monitor

One of the best examples of a new drought monitoring tool is the U.S. Drought Monitor (http://drought.unl.edu/dm). The National Drought Mitigation Center (NDMC), U.S. Department of Agriculture (USDA), and National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC) and National Climatic Data Center (NCDC) author the weekly Drought Monitor (DM) map, which was first released in 1999. The DM is not a forecast; rather, it was designed as a comprehensive drought assessment that reflects the existing drought situation across the country. Because multiple physical conditions may be present at once and no preferred scale exists for assessing drought, the DM also incorporates and heavily weights human expertise and judgment in the assessment of associated impacts.

The DM defines four categories of drought severity based on increasing intensity (D1-D4), with a fifth category (D0) indicating an abnormally dry area (possible emerging drought conditions or an area that is recovering from drought but may still be seeing lingering impacts). The drought categories represented by this scale are moderate (D1), severe (D2), extreme (D3), and exceptional (D4).

Several characteristics of the DM product make it unique and successful. One of its strengths is that the five categories are based on a percentile approach, where D0 is approximately equal to the 30th percentile; D1, the 20th; D2, the 10th; D3, the 5th; and D4, the 2nd (Svoboda et al., 2002a).

A second key strength of the DM product is that it is based on multiple indicators. One indicator is not adequate to represent the complex characteristics of drought across a region. Therefore, it is important that a product like the DM use a variety of quantitative and qualitative indicators. The key indicators used in creating the weekly DM map include streamflow, measures of recent precipitation, drought indices, remotely sensed products, and modeled soil moisture. Many other ancillary indicators are also used, depending on the region and the season. For example, in the western United States, indicators such as snow water content, reservoir information, and water supply indices are important for evaluating the current and future availability of water. These indicators inherently incorporate the effects of hydrological lag and relationships across space and time between climate and the surface or groundwater system.

The Drought Monitor also incorporates information from approximately 150 scientists and local experts around the country. The DM seeks corroborative impact information to provide added confidence in the initial assessments gained from purely quantitative information describing the physical environment. This kind of "ground truth" is important and increases broad-based credibility of the product with users.

The Drought Monitor has performed another equally important role by focusing discussions of drought issues and, in particular, the need for additional information and products. In this regard, the DM has been an unqualified success. Building on the U.S. experience, drought experts in Canada, Mexico, and the United States developed the experimental North American Drought Monitor (NADM) product in 2002 and produce monthly reports (http://www.ncdc.noaa.gov/oa/climate/mon-itoring/drought/nadm/). The NADM represents an important step in a cooperative, multinational effort to improve monitoring and assessment of climate extremes throughout the continent (Lawrimore et al., 2002). Other nations and regions have expressed interest in a product like the DM.

Products resulting from the DM process include the CPC weekly short- and long-term products, which "blend" multiple quantitative indicators used in making the DM. The two blends attempt to identify drought severity differences resulting from shorter and longer timescales. These products, known as the Objective Blends of Drought Indicators (OBDI), are available at the CPC website (http://www.cpc.ncep.noaa.gov/products/ predictions/experimental/edb/droughtblend-access-page.html).

Continue reading here: Climate Delivery Systems

Was this article helpful?

0 0