Wednesday, November 15, 2006

Forecasting Agricultural Drought in the Southeast USA.

Keith Ingram1, James Jones2, Soonho Kim1, Preston Leftwich3, and John Christy4. (1) IFAS, Dept. Agricultural and Biology, PO Box 110570, Gainesville, FL 32611-0570, (2) USDA-ARS, PO Box 110570, Gainesville, FL 32611-0570, (3) Center for Ocean Atmosphere Prediction Studies, Florida State Univ, 2035 E. Paul Dirac Dr, Tallahassee, FL 32310, (4) Alabama Office of State Climatologist, Univ of Alabama, Earth System Science Center, Huntsville, AL 35899

            Although annual rainfall generally exceeds annual evapotranspiration (ET), seasonal drought is common in the Southeast USA, particularly in during April-May and during August-September.  Sandy soils with relatively shallow rooting depths provide a meager buffer against rainless periods longer than 10 days.  While climatologists have monitored these droughts for the past several years, efforts to forecast drought in the Southeast USA are relatively recent.  The purpose of this research was to develop methods to forecast drought probabilities for Alabama, Florida, and Georgia, based on El Niño Southern Oscillation (ENSO) phase.  Because the historical climate database has both many gaps and stations with insufficient duration of monitoring to develop good probability distributions for the different ENSO phases, we used 250 years of daily data developed by bootstrapping methods for all cooperative climate stations in the three-state region.  We computed the Lawn and Garden Moisture Index (LGMI), which is a weighted 21-day sum of precipitation adjusted for an idealized seasonal ET demand.  An LGMI value of -1.5 or less is considered a drought severe enough to cause significant yield loss.  Results are presented as maps of the probability that LGMI will be less than -1.5 during three 10-day periods for each month of a given ENSO phase.