Using the almanac data from your website, in 2007 we received 83% of our average rainfall. In 2006, we received 125% of average. Going back another three years, we are still over the average. Looking at the Lake Level data, only Falls Lake is way below normal. Seems to me like Raleigh is simply using (or selling) too much water. Can you please comment on this? I don't understand why 83% of normal rainfall is an "exceptional" drought. Even before recent rains, we had received more than 75% of average. Thanks!!
Posted January 9, 2008
MIKE MOSS SAYS: Chris, There is certainly a component of growth and water use involved in the exceptional drought situation. However, this is a more widespread issue than just Raleigh drinking water and does have a basis in a very dry meteorological pattern across NC during much of 2007, compounded by extremely hot temperatures through the latter half of the summer that exacerbated the lack of rainfall by enhancing evaporation rates (and water usage rates as well).
One important point to note is that on a couple of occasions in the late Spring, mid Summer and later October, the Raleigh-Durham airport happened to receive rainfall from some limited-coverage systems that, all taken together, left the airport with a notably lower deficit for the year than many surrounding areas. The contours are a little low-resolution, but the attached maps showing estimated rainfall anomalies and percent of normal rainfall for our state help to illustrate this. While a small contour over western Wake County shows a deficit in the 6-8 inch category, look over toward western Durham, Orange, western Granville, and southern Person counties, for example, and you see large areas with 15-20 inch deficits for the year, with percentages more like 40-60%, much of which fell very early and very late in the year. To go along with this info, note that Falls Lake is fed by a rather small (770 square mile) watershed covering northern Durham, extreme northwestern Wake, northern Orange, southeastern Person and southwestern Granville counties, and there are two reservoirs in Durham county that intercept some of that runoff.
Meanwhile, Jordan lake draws some water from Guilford and southern Rockinhan counties in the Triad, where defecits were not quite as extreme, especially during the latter part of the year, and Kerr Lake is fed by some of the less dry area just north of there and up into southwest Virginia.
These are not the only indicators to consider, either. The groups that assess drought severity also looks at groundwater and streamflow levels, both of which have been down significanly as the drought has progressed (including surficial well failures in part of the state) and at soil moisture and crop moisture indices, along with the performance of crops themselves, which suffered very significant losses across much of the state during the summer and fall.
As an example, you might peruse the soil moisture ranking maps from the past year at
There, you can click on each month of 2007 to see a percentile ranking of soil moisture for the U.S. - for North Carolina, we started the year with rather moist soils due to heavy rains in late 2006. By summer and fall, though, soil moisture values for significant portions of the state fell into the brown "1 percent" category, meaning the soil was drier than 99% of readings taken during the comparison period for the percentiles, which covered the years 1932-2000. The next contour down indicates soils drier than 95% of years, and so on. In addition to these measures, a time series of an index for medium-term drought, called the Palmer Hydrological Drought Index, fell to the lowest value it has reached for a statewide average of North Carolina climate divisions since calculation of this measurement began in 1895.
That's a quick overview, and the AP also ran a story with a pretty good summary of the situation in a December article published in USA Today. You can see that story at