Drought Monitor classification for streamflow gaging stations
U.S. Drought Monitor classification applied to median of “daily” percentiles for 7-day average flow during the previous 7, 14, 30, 60, and 90 days at selected USGS streamflow gaging stations.
7 days |
14 days |
30 days |
60 days |
90 days

Explanation
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Unregulated |
Regulated |
| No - No Drought (>30 percentile) |
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| D0 - Abnormally Dry (21 to 30 percentile) |
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| D1 - Moderate Drought (11 to 20 percentile) |
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| D2 - Severe Drought (6 to 10 percentile) |
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| D3 - Extreme Drought (3 to 5 percentile) |
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| D4 - Exceptional Drought (0 to 2 percentile) |
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| n/d - Not determined |
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Map is assembled as follows:
- At each site, compute the “daily running” 7-day average flows and corresponding percentile based on historical 7-day flows for the given calendar date. See USGS WaterWatch pages for this particular statistic for each calendar day.
- Then for previous “x” days (where x = 7, 14, 30, 60, or 90), rank the computed daily percentiles and determine the median percentile for the indicated previous period.
- Relate the median percentile (corresponding percentile range shown in map explanation) to the U.S. Drought Monitor classification scheme for streamflow.
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