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Is development to blame for lack of rain?

A neighborhood activist wants policymakers and scientists to research his theory.


St. Petersburg Times, published March 8, 2001

ST. PETERSBURG -- It's not official and scientists are skeptical.

But a neighborhood activist wonders whether heavy development has reduced rainfall in the Tampa Bay area -- and thus contributed to the current water shortage.

Using computer spreadsheets and rainfall data going back to 1921, Steve Plice has produced graphs showing average rainfall since 1950 in St. Petersburg, Tampa, Tarpon Springs and Bradenton.

Meteorologists use year-by-year averages for 30 years to arrive at an area's overall average rainfall. For example, St. Petersburg's average as reported in 1950 was computed by measuring the yearly average rainfall starting in 1921; the 1951 average would have used data starting in 1922, and so on.

Plice found that average annual rainfall has decreased in St. Petersburg and Tampa, while Bradenton's precipitation has remained constant and Tarpon Springs' has increased. The average is falling most rapidly in Tampa, according to Plice's charts, with St. Petersburg second.

Plice's theory: Intense development causes the decrease, and as wetlands are paved, storm sewers channel rainwater into the bay rather than letting it seep into the water table. The resulting environmental changes cause less rain to fall, Plice believes.

"I can't prove it, but all the data I am able to gather make a strong suggestion," said Plice, the president of the Jungle Terrace Civic Association.

Two scientists contacted by the Times offered different opinions on Plice's hypothesis.

State climatologist James O'Brien said he doubts it is valid, but Charlie Paxton, a U.S. Weather Service meteorologist, suggested the theory could be an open question.

"I wouldn't rule anything out," said Paxton, noting that atmospheric dynamics are complex.

He also said more data are needed to answer the question.

"Just looking at a couple of sites doesn't really paint a complete picture. It would be kind of neat to look at rainfall from all the available sites to see if it's a trend that's occurring everywhere," Paxton said.

"There has been a noticeable decrease (in rainfall) since the '50s."

O'Brien argued that developed areas actually should generate more rainfall.

Cities such as St. Petersburg are "heat islands," O'Brien said. "They have all this concrete. Outside (the cities), you have trees and forests. Most cities would be warmer than out on the farm, so this provides convection that would tend to enhance rainfall."

Plice said he has heard about that theory, too. "But then from the historical data that's available, Tampa Airport is the driest place in the Tampa Bay area," he said. "You would think that with the airport and all its runways, it would be the wettest."

O'Brien, meanwhile, also pointed to fewer tropical storms as a reason for diminishing rain.

Plice, who has a master's in business administration from the Wharton School, also contends that rainwater running off pavement into drain pipes keeps the water table from replenishing.

Tree roots then have a harder time reaching groundwater and thus transmit less evaporated water into the atmosphere, which also contributes to rainfall, Plice speculates.

Paxton, though, said geography like Florida's means the Gulf of Mexico and the Atlantic Ocean are huge contributors of evaporated water, "much more than you get from vegetation."

Last month, Plice gave his findings to the board of the Council of Neighborhood Associations. And he would like policymakers and scientists to consider and further research his theory.

"For us as a city, we should look at our own development practices," Plice said. "We give variances to people very, very easily to allow them to cover more of their green space than the building code allows."

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