Or Shine

Rain or Shine Report for 12/26

TORTOISE vs. HARE UPDATE

The week before New Year is regarded by many working professionals as one of the easiest weeks of the year — and thus, as a result, it tends to make for peaceful days in the office — with relatively few distractions — or alternatively, a great time to take some time off to recharge the batteries with family and friends.

In the world of hydrology, however, we are confronted with stoney realism that the water cycle never sleeps, thus necessitating another installment of the weekly Rain or Shine Report.

Not surprisingly, this week was another week of no rain. That makes this year’s dry season almost 2 months long in the tooth. But that leaves us still with another 4 months to go.

I just got off the phone with a meteorologist over in West Palm Beach. He commented that “yes, another week of no (or little) rain” but added the additional wrinkle — and insightful observation — that while we often think of evaporation as being the constant performer during the winter — and that each passing week with no rain is another mark in the victory column for the slow-moving Tortoise gaining ground on the fast-moving (but winter hibernating) Hare — as from the fable of the Hare and Tortoise) — in actuality, the Tortoise isn’t as constant a performer as we give him credit for.

While more steady than the Hare for sure, a closer look at the fine-tune knobs of the water cycle reveal that the Tortoise actually slows down to a slow-motion crawl during the coolest part of the winter.

But be on a lookout for the Tortoise to pick up his pace with a spring-time sprint to the finish line at the end of the dry season. The Tortoise starts “kicking it in” sometime around March. By April and May the Tortoise is practically in a full gallop, that is, a full gallop by Tortoise standards.

YEARLY RAINFALL TOTALS

Late December is when we all start to think about the past year. That makes it a perfect time to take a look at our yearly rainfall totals.

The broad-brush main story line of the 2007 rainfall year was that plenty of rain fell along the east coast — do you remember Miami-Dade’s 13 inch and 10 inch rain totals in June and October — while the Lake, Kissimmee, and Southwest Coast largely missed out on those events.

But let’s also look at it with a finer brush.

Miami-Dade led the way in 2007 with 63 inches of rain. Lake Okeechobee was the caboose in 2007 with only 32 inches of rain. Where did the other basins fall? Southwest Coast (from Naples to Ft Myers) received 41 inches, Big Cypress National Preserve 48 inches, Kissimmee Valley 39 inches, Loxahatchee 46 inches, and East Palm Beach 55 inches.

Miami-Dade has actually averaged around 56 inches of annual rainfall over the past 10 years. Interestingly, this was the first year that Miami-Dade’s annual rainfall total topped 60 inches since 1999.

Compare that to Lake Okeechobee. It’s averaged around 44 inches of annual rain over the past 10 years, but has only received around 31 inches of rain in each of the past consecutive 2 years. In 2005, 53 inches of rain fell on the Lake. That was nothing compared to 63 inches that fell on the Lake during the El-Nino influenced 1983 year.

Compare that to the Kissimmee Valley. It’s averaged around 50 inches of annual rain over the past 10 years. That makes this year’s 39 inch and last year’s 33 inch totals well off the mark. In 2005, 57 inches of rain fell on the Kissimmee Valley.

Compare that the Southwest Coast. It’s averaged around 58 inches of annual rain over the past 10 years. This year’s 40 inches is off that mark by 18 inches, and was lower than the 44 inches of rain recorded during the 2000 drought. Big rainfall years of note for the Southwest Coast were 2005 (68 inches), 1995 (83 inches), and 1983 (73 inches).

Compare that to Big Cypress National Preserve. Its averaged around 57 inches of rain over the past 10 years. This year’s 47 inches was a similar to 43 inches that fell during our last drought year in 2000.

IN SUMMARY,

South Florida is a land of abundant, but distinctly seasonal, rains — and with very little surface storage. That leaves only limited space to store the summer rains — when they do fall — for a rainy day (or in this case dry day) when water becomes scarce in the spring. And as we saw this year, the summer rains can hit or miss geographically as well, either amplifying or soothing the water supply situation. Its that meteorologic mix that keeps south Florida on the delicate teeter-totter between drought and flood on an annual basis, and just a low or high season away from an extreme on either end.

Map shows monthly rain for major basins

relative to average for past several months.

Color-coded bars show actually monthly rainfall. Hollow line-drawn bars show averge monthly rainfall.

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