The green out of the cypress is a big swamp’s milestone:
The second half of the winter dry season has now begun.
The above bar chart reports the annual duration (in months) that the floor of the pond apple forest has gone dry in Big Cypress National Preserve, from 1992 to present. The years 2005, 2007, 2009 and 2011 also coincided with major wildfires.
The cooler temperatures of the first half (Nov-Feb) put evaporation on hold.
Look for it to heat up now that the second half (Mar-May) has begun.
That means water levels will start dropping faster and — more and more — surface water will be harder and harder to find. The place you find it last is in the center of the cypress domes and strands where the pond apple trees call home.
The surest sign that deep drought has hit the swamp?
Late March 2011
Answer: That’s when the pond apple roots become exposed. Last year it happened just for just two weeks. Two years before that (see photo above) over four months.
I‘ve been struggling for the past few weeks trying to refine my understanding of Florida fall. (By normal continental standards, there are many who say it doesn’t exist.) Just as I was getting some clarity …
I walk into the grocery store and see this:
Florida Navels are the first orange crop to ripen, thus marking the start of winter
Florida Navel Oranges mixed in among the continental apples.
That’s as sure a sign there is that winter has begun!
Some look to the skies for the absence of clouds. Others go by the feel of cooler (or less warm) temperatures. Still others look for the signs of dry ground.
While each has its merits, they are subjective and uncertain to a degree:
The tropics stay open until November’s end,
Sloughs and strands remain under water (even if the pines have gone dry),
And cloudless skies can still torch with summer-style heat.
My hunt for the “case-closed-gate-shut” sign led me to the S12A.
It quite literally shuts (stopping the water) on November 1st of each year.
The S12A is the westernmost of the four famed water control structures that deliver inflows into the northern boundary of Everglades Nat’l Park.
(They are revamping another closer to Miami – by means of a one mile bridge – which will incrementally increase flows into the main channel of Shark River Slough over the coming years.)
As for now, the other three S12 structures are still open,
But they too will close as the dry season progresses in the months ahead.
It’s been a relatively small inflow year for the Park –
Around 350,000 acre feet of water has discharged through the four S12 structures this year to date. The annual average discharge over the past 10 years has been 650,000 acre feet. The big flow year of record was 2,300,000 acre feet in 1995. The most recent big flow year was 1,200,000 in 2005.
As a result, water depths in Shark River Slough fell about 8 inches below the normal early fall peak. Current stage is also about 8 inches below early November of last year, almost 2 feet below the late October peak of the record 1995 year, and a half foot higher than the drought summer of 2007.
The summer drought of 2007 was an interesting year.
The S12s delivered a measly 30,000 acre feet of water into the Park – which, in comparison, is less than the annual flow volume down the diminutive Turner River here in Big Cypress Nat’l Preserve. As a result, the glades stayed contained in the ridge and slough lowlands of the park all year.
That year, the question wasn’t so much when the dry season began,