Spring Drought

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Intro - Sunshine or Rain State?

The subtle and interconnected nature of flood and drought

By Robert V. Sobczak

Drought in the swamp?

It almost sounds like a contradiction in terms.

audio introduction

But come every winter the water table (almost) reliably drops to the point, at some point in the spring, much of the swamp is bone dry.

Actually, the term "swamp" is a bit of a misnomer.

A better way to describe the habitats of the Big Cypress is as a mosaic.

Cypress strands, domes and dwarf prairies probably come to mind first. But almost half of the Big Cypress is comprised of the slightly higher-ground of marl prairies, pinelands and (a little higher up still) hammocks. And even deeper than the cypress are the pond apple and pop ash forests, marshes, sloughs and deepest of all - the alligator pools.

Not just a homogenous swamp, these habitats are mixed together in a distinctive pattern that is reflective of tiny topographic hills and valleys and the dual drivers of fire and flood.

Wildfire can occur any time in the swamp, at any season.

Recent Drought Charts

But it isn't until the winter dry season, and in particularly deep spring dry downs, when wildfire can spread quickly and widely across the landscape.

U.S. Drought Monitor

Day 1

Current Statewide Drought Map

Day 1

National Drought Map

Recent Blog Posts

dry season

Average rains
But still a drought

So far this winter dry season …

Except for December, we’ve had normal monthly rains.

Monthly rain in Big Cypress National Preserve

Compare that to last year where despite a wet November and December (of 2020), every month from January through May (except April) fell below the normal range. You’d think that would mean we’re much wetter today as a result, yet we’re not. Although we are not super dry either. The water table is hanging shallowly under land’s surface and the deeper holes are still wet. Take home points, there are two: (1) During the winter in south Florida, normal monthly rains still equates to a spring dry down and (2) no matter much rain the swamp gets the rest of the year, subpar rain in April and May causes the water table to nosedive into a deep spring drydown.

water cycle

Late March Update
Spring drought season begins

Not that there’s a major test tomorrow …

But the cheatsheets have been updated.

March is peak tourist season in the swamp and also the start of the spring drought season, as seen at H.P Williams Wayside Park near Turner River

That means if a colleague asks you a question about where the water is at, you can quickly refer to these sheets and present yourself as an expert, or hone the expertise you already have. So, what’s the latest? The big story is this: South Florida is at the front door of its two-month spring drought period. The Big Cypress is especially prone to drought because, unlike the Everglades that has a higher proportion of low-lying sloughs, the water table tends to drop deeper and longer below the cypress tree roots. Here’s a comparison of drought levels in the Everglades and Big Cypress.

Rainfall: Did you know that Water Year 2022 is entering it’s final month? In south Florida, the water year runs from May 1st to April 30th. With a month to go, South Florida wide rainfall has nudged up into the “normal range” of 43 to 51 inches per year. South Florida is predictably drier than central Florida, and especially the panhandle which is sopping wet.

Kissimmee-Okeechobee-Everglades: Okay, this is where it starts getting complicated. Why? Pumps, gates, regulation schedules. Do I need to say anymore? Fortunately, the cheatsheets are here to help you navigate it. In a nutshell, the Kissimmee got some rain, as indicated by releases from the headwaters near Lake Toho. Further down in Lake Okeechobee, water levels are tracking at the long-time (i.e. 25-year) year normal for late March. Water releases through the S-79 have been steady at around 2,000 cfs, which is in the preferred estuarine window as defined by Bob Chamberlain. Further down in the Everglades, water levels are highest in Everglades National Park, and also above average in Water Conservation Areas 1 and 2, but below normal for this year in Water Conservation Area 3A.

In sum, people always ask me: “Bob, is there a single index well we can monitor to tell use everything we need to know?” Answer: Unfortunately not. The good news is there are the cheatsheets.

dry season

Is dry season rain a paradox?
Winter rains are the exception, not the rule

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Question: Why do natives spend so much time standing in the shade?

Believe it or not,

It rains during the winter in south Florida.

South Florida skies are reliably sunny in winter and spring

Even more quizzical, some of those individual rainfall events can be quite large, gulley washers even. The big difference with dry season rains is that they simply don’t add up over a monthly scale. One two inch rain event (however impressive) plus 29 zeros add up to a whopping two inches of rain. Compare that to the typically 7-9 inch totals of the core summer wet season months of June, July, August and September.

The water table reliably and steadily drops during the dry season, starting in November and lasting into May, as a result of the lack of steady daily rains. The caveat is when a big frontal storms pass through. Unlike summer storms that tend to be more local in nature, a winter cold front can dump water across the entire southern peninsula.

Another factor is the cooler temperatures. Winter storms don’t lose as much of their water to evapotranspiration back into the sky. The result is that every drop of winter rain counts as two, and also has a longer “staying power” on the landscape.

That changes in the latter half of the dry season somewhere around the vernal equinox when daylight hours start to grow, the cypress trees green out and air temperatures start to rise. Without rains in March, April and May, the swamp nosedives into a deep drought.

Cycles of flood and drought

How deep and how long will the spring drought last?

Usually not too far into May and rarely into June. It only takes a few weeks (sometimes less) for the summer rains to lift south Florida out of drought.

In summary: Yes, dry seasons are wet, and that’s not paradoxical. Just don’t count on them too much.

dry season