John Grymes | 5/27/2005 2:10:02 AM
Persistent drier-than-normal weather this spring has resulted in the onset of near-drought conditions over much of Louisiana, reports LSU AgCenter climatologist Jay Grymes.
"Medium and longer-range outlooks do not indicate a high likelihood for a swing toward a ‘wetter’ climate pattern ahead," Grymes says.
National Weather Service/Climate Prediction Center projections for Louisiana for June, July and August indicate summer temperatures are likely to be near-normal to above-normal, and summer rainfall is expected to be near-normal to below-normal.
At this time of year, the potential evapotranspiration (PET) rates run on the order of 1.5 inch per week, with those rates expected to climb by mid-summer.
PET reflects the potential (P) rates of natural evaporation (E) and plant transpiration (T) that can be expected if there is sufficient moisture in the environment to meet day-to-day moisture demands. If the ratio of precipitation-plus-soilwater content compared to PET is high, the water "needs" of the environment are met. A low ratio indicates the possibility of moisture stress for vegetation. Prolonged low ratios are signals of possible failure without rain or irrigation relief.
"Assessing PET and moisture availability can serve as a good index of the relative state of health for crops in the field," Gyrmes explains.
Rainfall differences across the state tend to be greatest in summer (barring the influence of tropical systems), with southern Louisiana averaging roughly twice the amount of rain falling across the northern parishes.
"Therefore, even if rainfall over the upcoming weeks were to run near seasonal norms, this would not be sufficient to quickly offset the soil-moisture deficits that have accumulated during the spring, especially across the state's central and northern parishes," Grymes says.
From mid-April to mid-May, rainfall was less than half the norm for almost the entire state, with numerous parishes reporting less than 25 percent of normal rainfall. Roughly half of the state recorded less than 50 percent of normal rainfall from mid-March to mid-May.
Dry weather during March, April and early May led to serious soil-moisture shortages for much of Louisiana, with only the southeastern quarter of the state being spared.
"With outlooks calling for near-normal to drier-than-normal weather over the upcoming weeks, prospects are not especially good for rapid improvements in soil-water conditions without irrigation," Grymes says.
For information on related topics, visit the AgCenter Web site at www.lsuagcenter.com/. For local information and educational programs, contact an extension agent in your parish LSU AgCenter office.