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Tortoise and Hare of the Swamp
And why they both deserve participation trophies

South Florida’s water cycle …

Resembles the fable of the Tortoise and the Hare.

Rainfall is fast and evaporation is slow, but over a year they usually balance out.

Think of rainfall is the Hare.

Summer rains are drenching and drainage of the swamp’s flat landscape poor. That causes water to rise rapidly and stay there through the summer and into early fall. But come mid October the wet season ends.

That’s when the Hare falls asleep and the dry season begins.

The Hare sprints ahead from late May into early fall

Enter the slow and steady Tortoise:

Evapotranspiration is slow and steady worker – some would say inexorable. As dry season weeks turn into months and the Tortoise marches on, by some point in the winter and definitely by spring pretty much all the water in the swamp is gone. Or in other words, drought …

And yes, wildfires, too.

Come spring the Tortoise catches up

But not so fast.

All it takes is one big rainstorm for the Hare to wake up, hurdle the Tortoise and sprint ahead out of sight, but not for long. Unlike the real fable of the Tortoise and the Hare, south Florida’s annual race called the water cycle has no beginning or end. Or in more scientific terms: The swamp is a flood and fire adapted ecosystem. Every square inch of flora and fauna depend on a goldilocks dosage and return interval of flood and fire to maintain the health of the swamp mosaic.

And the winner is …

Moral of the story:

The Tortoise and Hare are both winners. Participation trophies for both!

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Tidbit: The south Florida rainy season lasts from mid May to mid October, or about 5 months.

Water Years 2021/2022 in Review
A brief comparison of the past two years

1. Water Year 2021 (May 1, 2020 to April 30, 2021)

Water Year 2021 classified as above average in terms or rainfall, recording 46 and 14 inches of wet and dry season rainfall, respectively, for a total of 60 inches.  The summer wet season started early with a June-like rain total in May (8 inches) and ended late with above average rains in October and a surprise storm in November.  Of note, the early start was not enough, or rather in time, to prevent a destructive incineration of an archipelago of hardwood hammocks in the southeast Corner of Big Cypress National Preserve called the Moon Fish Wildfire.  Within a week of the fire ending the May rains swept through.  Near normal rainfall persisted for core four months of the summer wet season (June through September) and were supplemented by a “wet season” like October.  But the real exclamation point came in November in the form of Tropical Storm Eta, filling the Everglades and Big Cypress Swamp to levels last seen in September 2017 from Hurricane Irma, only shifted forward two months to a time when water levels are usually well past their October peak. 

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The late season highwater stand set the stage for or prolonged and steady winter recession that proved to be a boon to wading bird communities in terms of foraging and nesting.  Despite expectations of a wet dry season from the bumper crop of summer and late fall rain, the Big Cypress Swamp dropped into deep drought by April’s end.  Although no similar wildfires occurred, Water Year 2021 proved an important restoration point:  No matter how wet the wet season or the beginning of the dry season, without timely April and May rains the Big Cypress Swamp is especially prone to dropping into deep, unnatural drought due to perimeter and interior canals that stifle the spread of sheet flow and hasten its spring demise. 

2. Water Year 2022 (May 1, 2021 to April 30, 2022)

Despite the previous year’s bountiful rains, Water Year 2022 took started slow thank to subpar rains in May – extending drought conditions into June and even July in some area.  However, the four core seasons of the summer wet season (June through September) and October all charted in with average rainfall.  For a second year in a row, November provided an unexpected boost with twice its normal rainfall amount. Again, despite the surplus of water at the dry season’s start, the Big Cypress Swamp was poised to drop into deep spring drought, imperiling the habits that so vitally depend on natural fire breaks staying wet, when a string of continental fronts at the middle and end of April and start of May boosted the water table just when it needed it most.  South Florida received over 10 inches less annual rainfall and 4 inches less dry season rain than the prior year, but it is as much an issue of timing as it is the total amount. Water Year 2021 classified as low normal in terms or rainfall, recording 36 and 12 inches of wet and dry season rainfall, respectively, for an annual total of 48 inches. 

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Did You Know: Up north on the continent, the water year starts October 1st and ends September 30th in most areas.

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Dual Calendar?
Julian vs Water Year

A year older, a year wetter

Normal people turn the calendar to a new year on January 1st. Not hydrologists — not even close. And rightly so. January falls in the middle of south Florida’s winter dry season. Starting the year anew in January splits the dry season in half — a big no-no if you’re trying to tabulate dry season rainfall and full year water amounts. The solution? Enter the water year. Up north on the continent the water year starts on October 1st (long story). The short story is that south Florida’s water starts anew May 1st each year on May 1st. Don’t expect a big parade or a big summer storms to magically start on cue on the first of the month. And to be certain, the first few weeks of May are usually dry. But make no mistake: It’s also the month that the humidity hammer drops and summer rain clouds start to emerge, even if it’s sporadic at first and usually doesn’t start in earnest towards the latter Memorial Day half.

The upside, and why hydrologists like me are adamant on this point: Starting the water year on May 1st allows us to split the year into two equal 6-month wet and dry seasons.

Dry season wrap up?
And why it's not over yet

The dry season isn’t over …

But it’s entering its final weeks.

Rainfall over the past 7, 30 and 90 days across south Florida

When does the rainy season start?

Afternoon showers can start sputtering in April and early May, but it isn’t until later in May and early June that the water table typically rebounds.

Whatever the case, the verdict is in:

The 6-month dry season was was wetter than average across the entire southern peninsula with the exception of the Upper Kissimmee and with the lower east coast leading the way. District-wide, south Florida averages around 13 inches of rain compared to the 15 inches recorded this year.

Basin by basin comparison rainfall since the start of the dry season (blue) and the start of the calendar year (red). The hollow black bar shows the dry season average.

But May is a pivotal rain month.

Typically drought extends and deepens in its early half before the afternoon showers kick in or we get a big regional storm.

One more week, and Water Year 2022 is here!

As usual, it’s a wait and see.

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