Agricultural Drought Indices - US Department of Agriculture
Agricultural Drought Indices - US Department of Agriculture
Agricultural Drought Indices - US Department of Agriculture
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The North American <strong>Drought</strong> Monitor: Three years after the <strong>US</strong>DM was launched, the North<br />
American <strong>Drought</strong> Monitor (Lawrimore et al. 2002) (Figure 5) debuted in 2002 as an “experimental”<br />
monthly product that is forged out <strong>of</strong> a partnership between several entities in Canada, Mexico,<br />
and the United States. Since that time, the experimental label has been shed. As with the U.S.<br />
<strong>Drought</strong> Monitor, the NADM blends science and art. There is no one “correct” way to measure<br />
drought. <strong>Drought</strong> indices are used to detect and measure droughts, but different indices measure<br />
drought in different ways, and no single index works under all circumstances (Heim 2002). The<br />
ranking percentile principal is the same, but the inputs vary slightly depending on which<br />
parameters are readily available to the respective agencies involved in each country. As the<br />
process stands now, each country follows the same basic methodology, utilizing their own<br />
indicators to depict drought conditions within their borders. The monthly author (which rotates<br />
between the three countries) is then responsible for working out the merging <strong>of</strong> the GIS shape files<br />
and reconciling any disputes along the borders. Impact and data information are exchanged in<br />
working out any differences in an iterative fashion until all issues are resolved. More information<br />
and details on the NADM can be found at http://www.ncdc.noaa.gov/temp-andprecip/drought/nadm/index.html.<br />
Figure 5. North American <strong>Drought</strong> Monitor for January 2011. (http://www.ncdc.noaa.gov/temp-andprecip/drought/nadm/nadm-maps.php)<br />
The Objective Blends<br />
Over time, the <strong>US</strong>DM authors have been asked at various pr<strong>of</strong>essional meetings and forums why<br />
we do not create two separate <strong>US</strong>DMs for the short- and long-term periods and why we do not<br />
have a Flood Monitor. The questions have been relatively simple to answer: decision makers want<br />
one map with one number to interpret and the media want one product to display and disseminate,<br />
whether it be for droughts or floods. As a means <strong>of</strong> addressing the need for two maps and for<br />
those wanting to dig deeper into the science, a short-term (agricultural) (Figure 6) and a long-term<br />
(hydrological) (Figure 7) OBDI were initially tested experimentally over a 12-18 month period and<br />
are now used in giving an automated, computer-generated snapshot each week by climate division.<br />
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