Published: 2007-09-19 10:23:46
Updated: 2007-09-19 10:23:46
Posted September 19, 2007
By Joe Freeman
MIKE MOSS SAYS: Joe, a couple of things play into the apparent disconnect you've noticed. One of those is the fact that values for "rain needed to end the drought" or lesser values of "rain needed to ameliorate drought conditions" are calcuated for multi-county climate divisions (there are eight in North Carolina) rather than station by station, and are based on hydrological drought indices that take into account rainfall deficits, groundwater levels, streamflows, reservoir levels and so on. This year, there have been a few rainfall episodes that left RDU with a relatively smaller rainfall deficit than many surrounding areas, including those just upstream in portions of the Neuse and Haw/Cape Fear river basins.
In addition, if the newspaper article cited a need for 24 inches of rainfall to end the drought, it should have included a time period requirement for that amount of rainfall to properly put it in perspective. For example, calculated values for ending the drought within a two-month time frame indicate a requirement for at least 15-18 inches, while ending the drought over a six-month period would require at least 24 inches of rain (and seems likely to be the assumption quoted in the article you saw). If you'd like to explore some of these figures yourself, the National Climatic Data Center maintains a useful web site with nationawide drought termination values at http://www.ncdc.noaa.gov/oa/climate/research/drought/current.html.
I can't really speak for media beyond myself in terms of your comments on how the rainfall episode would be interpreted, but I don't really see it as being an either/or issue. I tried to make the point in my weathercasts that the rain on Friday was both a significant, helpful event AND that it was a small dent in the drought that would require follow-up periods of rainfall to make continued improvement.