Dec 17, 2013

Move over water cycle

Florida's summer water cycle focus is rain,

But come winter (and especially spring) drought rears its head.

Current KBDI levels
Click to enlarge

The figure above shows drought levels across Florida for (from left to right) today, a month ago, a year ago, and the long-term median for today.

Interestingly, Florida doesn't have a single drought index.

The animated map above shows Florida's median annual atmospheric drought cycle, as based on the Keetch Byram Drought Index (KBDI), over the past ten years. So often I had found myself turning to the Florida Forest Service's county-by-county daily KBDI map to get a handle on current drought conditions across the state, but the problem was the it only showed current conditions, thus I was always left scratching my head:

How do current conditions compare the statistical past?

Animated map showing Florida's
state-wide KBDI drought cycle

So what does the map say?

Most evident is that drought does not descend equally across all parts of the peninsula, nor at the same time, but there are also interesting wrinkles, too. Over the typical annual cycle, for instance, drought severity peaks the highest (but for a relatively short-lived time, i.e. late spring) in the Big Bend area. Compare that to south Florida where atmospheric drought occurs over a more protracted period, i.e. late fall, winter and most of spring, but at a lower amplitude. The wrinkle for south Florida is that the KBDI is an imperfect index for tracking drought because it doesn't account for the lingering presence of summer water in its vast wetland mosaic, (i.e. poor drainage allows the Everglades and Big Cypress Swamp to stay hydric long after the summer rains end).

Not that the water cycle vanishes during the winter.

Actually, Florida's water and drought cycles work together hand in hand.

No comments: