Have Florida's daily rain patterns been thrown off by development and climate change?
Florida's known for daily afternoon rains.
Folklore says you can set your watch to the predictable showers and thunderstorms that help fuel our wet season.
But some researchers and ecologists fear daily afternoon showers may no longer be consistent: The drainage of the landscape over the past century combined with climate change has altered the 24-hour summer cycle.
"I think we are getting more days with no rain, then more intense rainfall events when we do get rain," said Win Everham, a professor and researcher at Florida Gulf Coast University. "Summer rains seem more like the dry season cold fronts."
Everham says South Florida's drainage network — a vast series of canals and ditches built to drain the Everglades for farming and development — works too well and moves water off the landscape before it has a chance to recharge wetlands and aquifers.
He's not alone in thinking the daily patterns have changed.
"That's my perception from living here for a long time," said Calusa Waterkeeper John Cassani. "Scientists like to go on data and we’re working on it, but there is some data out there that shows in parts of Florida rainfall patterns are changing."
Changing rainfall patterns could be problematic for native species, especially amphibians and other critters whose lives are tied to historic rain patterns.
"The surface water systems and wetlands are what us ecologists are really concerned about and certainly groundwater plays into that," Cassani said. "A pig frog needs over 200 days of a hydrated wetland to complete its lifecycle."
Research has shown that Southwest Florida has lost tens of thousands of acres of wetlands in the past few decades.
Those wetlands are habitat for amphibians and other critters.
If the rain pattern were to change, it could create the perfect scenario for invasive plants and animals, both of which have plagued the state in developed areas.
"My feeling — and I'd like to confirm that with a hard look at the data — is we no longer have the relatively consistent afternoon shower associated with summer," Everham said. "I think the annual totals may still be averaging the same, though there may be more variation around that mean, and there may be shifts in seasonality."
Jim Beever, a retired biologist and climate change and planning expert, said climate change is the main cause of any changes in daily rains.
"The pattern of increased drought and longer dry season with shorter more intense wet seasons with the same amount of rain compressed into storms with higher rates of precipitation is a result of large-scale climate change in Southwest Florida," Beever said. "I think climate change is a major and more important part of it.
"The removal of forests, swamps, and marshes does reduce evapotranspiration and the generation of clouds. And if you keep track of the daily and longtime weather like I have since the 1970s, you will see how precipitation over forests and swamps is always the most dependable."
Some hydrologists believe the change in daily rains could be due more to development than an over-drained landscape.
"(Renowned Everglades conservationist) Art Marshall feared a collapse of the summer rain machine if the Everglades weren't saved, and if I'm not mistaken used that as a thrust of his conservation mission to the public up to a point, until it was either later debunked, or never proved to a point that it caused it's complete demise," said Big Cypress National Preserve hydrologist Robert V. Sobczak. "There have been papers if I'm not mistaken showing slight changes to the regional rainfall pattern due to urbanization. The presence of the Gulf and Atlantic buffers that effect to some point, as it supplies steady moisture and humidity."
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If there has been a change in the daily delivery of water, it doesn't seem to be a big topic among farmers.
Gene McAvoy, with the University of Florida's agriculture extension in LaBelle, said he feels like day-to-day weather has probably changed since he moved to the area in 1989.
"I'd really have to look at some data, but I have no doubt the weather is changing," McAvoy said. "In summer you tend to get these afternoon storms but we see them in the morning and then we got a storm last night."
Shawn Clem studies rain as part of her job as research director of Audubon Florida's Western Everglades Research Center
She said overall rain totals haven't changed in recent decades, but that the theory of changing daily patterns may hold weight.
"The total over time hasn’t changed and our data set goes back to the 1960s," Clem said. "We’ve lost so many ranches — and open spaces have gone from agriculture to development — but we haven't been able to see it on that level. There may be a change, but there’s so much variability in our data."
Cassani said much of the state has experienced tremendous growth over the past 20 years and that climate change is only making the situation more dire.
"It’s a combination of over-development and over-draining of the landscape that disrupts the natural hydrologic cycles," Cassani said. "It brings a suite of stressors that climate change is just magnifying. Not only do we have altered hydroperiods but what we have is increasing trends for warming, and so that systemically has an effect on how plants and animals reproduce, how they migrate and their life history."
Clem said the idea that daily rainfall patterns have changed makes sense to her, although she hasn't analyzed the data to look at rainfall times each day over a period of time.
"I would expect to see it," Clem said of the data needed to confirm Everham's theory, Clem said. "It’s a really important ecological question. Maybe we’re getting the same rain but it's spotty and spatially on the landscape and it seems like early in the year it is spottier."
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