Monthly rainfall for Big Cypress Nat’l Preserve. Can you see the lull?
Someone once described it to me as the lull that sets in between the last of the continent’s spring time fronts and before the tropical waves really kick in. Over the long term that’s resulted in consistently (slightly) less rain in July than the other four core wet season months (i.e. June, August and September).
When will the wet season get its groove back?
Answer: Probably with a tropical storm. August, September and October are south Florida’s peak storm months.
It’s called the water cycle, and more specifically — the wet and dry seasons. Unlike Up North on the continent where they have four traditional seasons, the swamp has two, meteorologically speaking at least. So, in the way of a quick review: Last wet season got off to a slow start. The water table didn’t bottom out until mid June in some places, usually a reliably rainy (if also soaking in and rising up) month. Compare that to this year’s rainy season which — thanks the Big Rain Day (BRD) this weekend — is off to a fast start. Or rather normal. The blue line (current condition) is tracking very closely with the long-term norm (white line). In summary: The swamp rises and falls. Currently it’s rising. And looking back, has there every been a 9 month span that the water table tracked so closely to the long-term normal — I wonder? If so, it isn’t a trend I expect to last.
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!
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.
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 2022took 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.
Don’t get me wrong: The four seasons are great. And let’s also not forget, officially they are celestially defined by the position of the earth’s tilt as it rotates around the sun even. That being said, we tend to think of them meteorologically the most, or in other words, in terms of the weather.
That’s where the seasons and the calendar year for that matter fail us in Florida. For one, the meteorological seasons are skewed quite significantly from the normal continental norms. Summer-like weather lasts for six months, not three. And when fall weather will arrive is anyone’s guess. As for winter the season, it’s more accurately defined by a spattering of days. And spring? I’m not really sure other than the air is drier but it can get quite hot.
Using January as the start of the year in Florida is also a complete fail. (Talk about getting the New Year off on the wrong start!) Why? January is smack dab in the middle of Florida’s dry season. How can we start a new year when the season still has another 4-5 months on the books? That’s where the water year comes in handy. It starts in May when the water table bottoms out and the wet season is about to begin.
So the big solution calls for a two-pronged approach: We replace the water cycle with the seasons and aligning our new annual clock with May, not January, as the start of the new year. And here’s the twist: we don’t have to drop the seasons and calendar year completely. We keep them in the mix, too. It’s not about replacing the old regime completely, it’s about custom crafting it to fit into Florida’s unique meteorologic mold.
The water year, wet season and dry season help us simplify the seasonal math.