Mixed signals

I remember this cloud well:

It seemed a clear sign the summer rains were about to begin.

Calm before the fire
April 29th 2011

Instead it brought lightning and put the swamp ablaze.

It was the year of our drought of record and the Jarhead Fire.

Moral of story: Never trust a cloud!

Just to double check

How deep is the drought?

Judging from this marl chip, seasonally dry at least.

A drought-dried marl chip

A better metric would be to walk into the dome.

Ideally in April it’s peat would still be dry.

But why waste the time when I can see the answer right at my feet.

Drought exposed limestone
of the Tamiami Canal

Judging from the canal, the water table has dropped …

To the point that most of the domes have gone dry.

I walked to the dome anyhow.

Tortoise pulls ahead

If the Hare is rainfall,

And the Tortoise is evapotranspiration …

The Tortoise has pulled ahead
in south Florida’s annual water
cycle race

Make it official:

The Tortoise has pulled ahead.

Absent the a good frontal shower or three (i.e. the Hare waking up) we are on track for a pretty good spring drought until the summer rains (or do I mean Hare?) return.

Mixed signals

Finding some dry marl chips out there …

At the same time I’m seeing the build up of afternoon clouds.

Looks dry here,
but I drove through
an epic deluge on
my ride home

A transition is underway in the swamp.

Green out marks “shift” in swamp

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.

Citrus crop signals fall’s end

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!

Engineered fall

The dry season is here … finally!

How do I know?

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,

But rather how the wet season never got started.