Greater Everglades

Once a single interconnected system, the modern-day Everglades is a managed system of basins separated by levees and canals and connected by pumps, gates and the ongoing restoration and water management works. | Greater Everglades | Kissimmee | Okeechobee | Caloosahatchee | River of Grass | Big Cypress Swamp | Rainfall | Quick forecast | Drought outlook | Cheatsheets | Return to main blog

Intro - A Sum of Many Parts

One water cycle, many pieces, and lots of moving parts

By Robert V. Sobczak

Introduction

In Central Florida, rain collects in springs and lakes that flow into the Kissimmee River. The water then flows south into Lake Okeechobee to join water already stored. Lake Okeechobee is shaped like a very large, shallow bowl. Historically, when large amounts of water were collected in the lake, water would overflow its southern edge and flow into the Everglades. Today, water flow out of the lake is via canals that pass through the Everglades Agricultural Area. The water then arrives and flows through the Everglades before eventually reaching Florida Bay and the Gulf of Mexico. 

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The Everglades has a unique hydrologic, or water cycle. Throughout most of the continental United States, water levels generally rise and fall in tune with the four seasons. There, water levels typically peak during the spring as snow melts and front-driven storms move through, and ebb in the fall at the end of the hot summer. In contrast, the water cycle of subtropical south Florida and the Everglades is fueled by only two seasons—wet and dry—leading to a reversal of the typical seasonal high and low water levels. Water levels in the Everglades peak in the fall at the end of the wet season, and ebb in the spring when large expanses of wetlands dry out, at the end of the dry season. 

wet season

Summer Wet Season

The wet season typically begins in mid to late May and is characterized by hot and humid weather, daily buildup of spectacular cloud formations and resultant heavy thunderstorms that are often localized and short in duration. Other larger systems—including early season storms enhanced by lingering springtime instability in the upper atmosphere, mid-latitude cyclones and tropical storms—periodically spike the Everglades with regionally expansive rains.

In response to these meteorological inputs, the Everglades becomes flooded with an ankle to waist-deep, slow-moving pool of water throughout summer and fall, leaving only the high-ground tree islands and hardwood hammocks above water. The term sheet flow is used to describe this shallow and spatially expansive wetland plain that, unlike a lake or bog, flows like a stream, only much more slowly, almost imperceptible to the human eye. Spanning from horizon to horizon, this sheet of water flows south through a maze of tree-island-dotted ridges and sinuous low-lying sloughs, giving rise to the name River of Grass coined by Marjory Stoneman Douglas in 1947. 

dry season

Winter Dry Season

As the weather turns milder in October, the regular buildup of afternoon thundershowers and tropical storms ends, ushering in the dry season in mid to late November. As the dry season ensues, water levels continue to drop without much additional rainfall and more land emerges. Water first recedes from the highest elevation pinelands and other tree islands. Drainage of the marl prairies follows next, leading to an eventual retreat of water into the lowest-lying sloughs and marshes. The rate of recession may be slowed or even temporarily reversed by sporadic winter rains that are typically brought on by the descent of cold continental air masses from the north. Lower winter evaporation rates also hinder the rate of recession, though it rapidly picks up again in spring as daylight hours and air temperatures increase evaporation. South Florida is generally considered a wet area by merit of its abundant average annual rainfall, a total of 52.7 inches in the SFMWD region, with a 70/30 percent wet/dry season split.  Despite the often flooded wetland views, drought and wildfire play vital roles in maintaining the region’s unique assemblage of flora and fauna. The ecological health of the Everglades is intimately tied to seasonal and interannual fluctuations of the water cycle.

Recent Blog Posts

Water Year 2017
Dry October makes for long dry season

Water Year 2017 (May 1, 2016 to April 30, 2017)

Water Year 2017 featured a ”normal” wet season and “below average” dry season ― 40 inches of rain fell across south Florida during the six-month (May through October) summer wet season with 7 inches falling in the six month (November through April) dry season that followed, for an annual total of 47 inches. 

Accordingly, wetlands and waterways of the Everglades filled up through the summer wet season and reliably receded during the winter dry season months.  The biggest boost of rain came in August (an in particular in Water Conservation Areas 1 and 2 were 12 inches were recorded for the month) resulting in slough water depths to crest at a 2 foot depth through much of the Everglades by early October, more or less coinciding with vast wetland’s normal annual peak ― but one that, too, was also short lived. 

Continuing a decade-long trend of anomalously low tropical storm activity, October (a month which historically accounts for a quarter of Florida’s hurricane-strength storms) had little rain to offer, thus ushering in an early start to a winter recession of water, and one that would last particularly long.  Of note and continuing a two decade trend, the spring dry down was especially pronounced in the Big Cypress Swamp as evidenced by Corkscrew Swamp’s central marsh drying out and the outbreak of a large wildfire in Big Cypress National Preserve.