Apr 26, 2012

Does Florida only have three seasons?

I overheard somebody say "we didn’t have a winter this year" …

As if to imply we only had three seasons.

The above chart shows reports "south Florida wide" weekly rainfall.  The dotted line shows the long-term running 7-day average and the solid line shows the long-term running 7-day median.  Florida's three seasons are shown across the top of the chart.  Can you see how we are nearing the end of the "low rainfall and high ET season" and moving toward the "high rainfall and high ET season?"  Notice, too, how last weekend's rain was our rainiest event of the dry season.

I interjected, affirming that “I couldn’t agree more.”

“We have our (1) high rainfall and high ET season (June to October), (2) low rainfall and low ET season (November to February) and (3) low rainfall and high ET season (March to May).


“Actually, in south Florida there are only two?” the person corrected,

“There’s the summer wet season and the winter dry season.”

The above chart shows the relation of south Florida's two meteorologic seasons, i.e. wet and dry, with the landscape hydrology of the swamp.  The typical duration of flooding in major swamp habitats is also shown.

“Meteorologically yes,” I confirmed,

But in terms of landscape hydrology there are actually four, as follows:

  1. Soaking in season The early part of May is usually the crunchiest time of the year to walk through the swamp: water is absent except in its deepest pools, but by month’s end the wet season will have started, followed by June – the rainiest month of the year; yet only rarely do waters peak this early, thus making it a “soaking in” season during most years.

  2. Sheetflow season. The onset of summer, lasting into early Fall, coincides with an extensive but ephemeral sheet of shallow and flowing in the swamp. It’s flowing aspect is achieved when waters rise to the base of the hydric (i.e., a depth of 20 inches in the pond apple swamps) pinelands and higher. The depth, spatial extent and flow rate of sheetflow typically peak between late August and early October.

  3. Hydrologic Interregnum. Starting with the demise of sheetflow in mid fall and lasting through winter is the hydrologic interregnum. This is an approximate 5 month period in which water is still present on the ground, but no longer flowing and slowly receding from the landscape. In this way it defines the lag between the end of the meteorologic wet season and subsequent terrestrial drying, which is habitat dependent. March makes its end with drying the tall cypress, leaving water only in isolated pond apple forest, marshes, and refugia pools.

  4. Spring drought. Mid March and most of May mark the driest part of the dry season. The final third of the meteorologic dry season is punctuated by increased evapotranspiration, often accelerating the decline of water table and desiccating the surface, increasing susceptibility to wildfires.
Not your typical "four season,"
But four nonetheless.
As usual, this was a conversation that would need to be continued:

In the meanwhile we agreed it could be anywhere between two and four!"

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