Published: 2009-11-23 10:25:54
Updated: 2009-11-23 10:25:54
Posted November 23, 2009
By Mike Moss
At least the designation of such for parts of our state by the national Drought Monitor. In last week's post reviewing the heavy precipitation associated with Ida's remains and a follow-on nor'easter low, I wondered how the committee that assesses nationwide drought impacts would adjust conditions across our region.
You'll recall that much of North Carolina received on the order of 3-6 inches of rain from the combination of Ida's remnants and the nor'easter low along the coast over roughly 10-13 November. The people (both nationally and within the state of NC) who make the call as to how drought or dry weather is categorized took those rainfall totals into account together with information on soil moisture, long and short-term precipitation anomalies, streamflow data, lake level responses, groundwater reports and more, and entirely removed a severe drought area from south-central NC and a moderate drought area from much of central NC, and also reduced the area designated abnormally dry and removed agricultural impacts from the abnormally dry area, which did remain in place from just east of the Triangle area down across the Sandhills and southwest coastal plain (yellow shading in the first attached image).
While streamflow across the region spiked following the heavy rains and has tapered to levels a little above those preceding the storm, and local lake levels remain about 1-2 feet above normal (down about 1-3 feet from post-storm peaks - see the second image for a look at Falls Lake), and shallow soil moisture certainly remains elevated, they also had to consider longer-term precipitation trends and water table levels when choosing how to update the hydrologic state. For example, a running precipitation anomaly for one year at RDU shows about a 5.5 inch deficit even after those heavy rains. Likewise, a map of rainfall anomalies for NC covering the past 6 month period (third image above) indicates a sizable area, corresponding roughly to the remaining "abnormally dry" drought monitor contour, with deficits of 2-5 inches over that span, and also includes smaller areas in Johnston, Cumberland and Moore counties, for instance, where the 6-month deficits still exceed 8 inches. Finally, groundwater monitoring wells remain around a foot and a half below long-term median levels with most wells in the area showing readings in the lower 20-40 percentile range. With even modest rain in the coming weeks and months, the drought monitor committee may well be able to remove the "abnormally dry" area (maybe sooner rather than later). Something to watch for, as it would be nice to see our state once again free of any shading on that drought monitor map...