Mar 25, 2014

Why the "previous" wet season still matters

Here's a look at dry season rain totals, from 1970 to present.

Is anyone else surprised to see this year (so far) is tracking low-normal?

The above bar chart shows a historical comparison of dry season rain totals in Big Cypress Nat'l Preserve from 1970 to present.  Dry season is a little difficult to quantify in south Florida.  Typically it begins the day the previous wet season ends (which can be mid October) and ends sometime in mid May when the new wet season starts.  For comparison purposes, the dry season in the above chart is defined for the six-month period from November through April.  This year's bar (on the far right) can potentially still grow -- we have another six weeks to go before April is through.  A normal dry season ranges between 7 and 14 inches of rain, with an average of 11.5 inches.  Our wettest dry season in recent past was the El NiƱo spring year of 1998 with 25 inches, our driest spring of 2009 when only 3 inches fell.

The reason I say that is that water levels are tracking slightly above normal for this time of year.  At first glance that would seem surprising, but don't forget (1) we still have another 6 weeks of dry season left (i.e. to make this year's bar fully comparable with year's past) and (2) how high the water table in March is as much a reflection of the rain that fell the previous wet season (i.e. June through October) as the previous three winter months (i.e. December through February).

Not that dry season rain doesn't matter.


But it does matter less when the summer before was so wet.

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