Wetland Draining May Have Hurt Crops
Some crop-damaging freezes in south Florida might have been milder or avoided completely if wetlands in those areas hadn't been drained years ago for farming, a new study suggests.
The work emphasizes that land use is one of "a multitude of ways humans are affecting the climate system," said Roger Pielke Sr. of Colorado State University, one of the study authors.
He and colleague Curtis Marshall report the results in Thursday's issue of the journal Nature, along with Louis Steyaert of the U.S. Geological Survey.
They focused on an unexpected 1997 freeze in southern Florida areas that used to be wetlands. The freeze cost vegetable and sugarcane growers some $300 million.
Starting with weather conditions recorded from before the freeze, they asked a computer to simulate what would have happened if the areas had remained wetlands.
Then they asked what would happen assuming the land-use conditions were the same as those present in 1993. They chose 1993 conditions as the latest available estimate of what the land was like in 1997.
The study contrasted the outcomes under the two simulations. It indicated that if the wetlands had remained untouched, temperatures in most of the areas would have stayed in the mid-30s to upper 30s, avoiding a freeze. In other wetlands areas, the freeze would have happened, but it would have been milder and briefer than the outcome calculated with the land switched over to agriculture.
The duration of a freeze can be just as important as temperature for determining crop damage, Marshall said.
The researchers got similar results when studying crop-damaging freezes in south Florida that occurred in 1983 and 1989.
Wetlands can ward off freezes in two ways, the researchers said. First, the standing water moisturizes the atmosphere, which can then better trap heat that radiates away from the ground at night. Secondly, wetlands provide warmth because water can retain heat better than drained lands, and release heat when wetlands start to freeze, Pielke said.
Jim O'Brien, the Florida state climatologist, said the study's conclusions were no surprise. "To me, it's just common sense," he said.
O'Brien also said that while wetlands can ward off freezes that happen when the land gives up heat, they're ineffective when cold air masses roll in from somewhere else.
The researchers agreed, but Marshall said the vast majority of freezes south of Lake Okeechobee are due to the heat-radiation effect.
Created on ... November 05, 2003