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Southeastern United States Hurricanes: Shining a Light on Their Positive Side
Knight, D.B. and Davis, R.E. 2007. Climatology of tropical cyclone rainfall in the southeastern United States. Physical Geography 28: 126-147.

Noting that "most of the media and scientific attention to hurricanes emphasizes the conditions at landfall, when most damage occurs," the authors write that "the climatological contribution of tropical cyclone-induced rainfall is often overlooked." Consequently, they focused on this bright side of the feared phenomenon, investigating the role of hurricane-induced precipitation in meeting the water needs of southeastern U.S. farmers.

What was done
Using meteorological data from 84 surface observations stations stretching from Texas through Pennsylvania (also including Alabama, Arkansas, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, New Jersey, North Carolina, Oklahoma, South Carolina, Tennessee, Virginia, Washington DC, and West Virginia), Knight and Davis calculated the amount of hurricane-induced rainfall at each location for each year's hurricane season (June through November) for the period 1980-2004, after which they evaluated the significance of their results for the agricultural enterprises of the affected states.

What was learned
The two researchers report that the hurricane-induced component of average hurricane-season rainfall ranges from less than 2% in parts of Texas to more than 15% in the coastal Carolinas. In addition, they say it "comprises a substantial percentage of the annual June-November precipitation in the coastal plain and Piedmont regions of Virginia, North Carolina, South Carolina, and Georgia," and that "Florida and parts of the Gulf Coast also receive more than 10% of their annual hurricane-season precipitation from tropical cyclones." With respect to the significance of this phenomenon for agricultural crops grown within these areas, Knight and Davis say that "soil moisture deficits are often highest when many plants are experiencing their final growth just prior to harvest," and that if all tropical cyclone-induced precipitation is removed, this deficit increases by as much as 65% in parts of the studied region, noting that "in the majority of the prime agricultural region of the Southeast, deficits would increase by approximately 20%-30% if the area did not receive rainfall from tropical cyclones."

What it means
Knight and Davis conclude that "rainfall from hurricanes is clearly important to the soil water balance," and that "the frequency and intensity of soil moisture deficits would significantly increase in many locations if not for rainfall from tropical cyclones," noting that "this obviously would have significant consequences for agriculture and would increase reliance on irrigation." Hence, they state that "despite the obvious dangers associated with tropical cyclones, both the ecosystem and the success of the agricultural enterprise in the southeastern United States in a sense depend upon them."

Reviewed 16 January 2008