After the recent rain from Hanna, what is the status of the drought and underlying water tables in the Raleigh area?
Posted September 9, 2008 10:27 a.m. EDT
MIKE MOSS SAYS: Carol, As you're aware, Hanna and the substantial rains (see the first image, from the Raleigh NWS Office) that fell in association with the remnants of Fay have resulted in significant additions to already full or nearly full surface water reservoirs and large short-term upticks in stream flows across the area. They also have had some measurable impacts on groundwater levels (at least in surficial groundwater) so it will be interesting to see how the drought designations fare over the next two weeks. There will be an update coming up on Thursday based on assessments by the NC Drought Management Advisory Council and the U.S. Drought Monitor group, which will look at groundwater responses along with soil moisture, surface water supplies and the flow rates (and especially persistence thereof) of creeks, streams and rivers across the region.
Just to throw out a couple of numbers, though, rainfall at RDU is now about 9.3 inches above normal for the past 90 days and 6.6 inches above normal over the past 365 days, and Falls and Jordan Lakes rose as high as 5 and 6 feet above normal in the day or two after Hanna. In addition, a real-time groundwater well at Chapel Hill that has shown persistently low water levels even after some of the Spring and Summer rains across the region has started to respond more favorably, with the level climbing quickly over the past week or two (second attached image). You'll see on the graph that the water level there is still well below the median for this time of year, but it has at least climbed into the green "normal" range of variability after having been in the red (lowest 10 percent of historical values) for a good long time. One thing to note is that the most recent few week of data is "provisional" and we'll want to see that there isn't anything wrong about the recent readings, which do appear to be rising awfully fast during September even in the wake of such notable rains. Hopefully these will prove to be valid readings.
Stay tuned, as I'm sure we'll be featuring the new drought maps on the air at times Thursday evenings and Friday mornings this week and next, and of course you can find them on our web site under the 2007-08 Drought link from our main weather page as well.