Lake Okeechobee is the jewel in the middle of Florida, with an approximate area of 730 square miles. Among natural (not man-made) lakes, it is the 9th biggest by area in the United States; the 4th biggest entirely within the United States; the 3rd biggest in the Continental United States; and the 2nd biggest wholly within a single state, next to the Great Salt Lake. That makes The Big O, as it is called locally, the largest freshwater lake in the lower 48 that is wholly contained within a single state's borders. But the lake is at historically low levels, as south Florida suffers through an unprecedented drought.
Some lakes, even relatively small ones like the Finger Lakes of New York, are so deep that it would be virtually unthinkable for them to disappear. Not so with the big O. With an average depth of around 10 feet, the volume of water in the lake, about a trillion gallons, could entirely evaporate in a prolonged dry spell.
Climatology of the Lake Okeechobee Area
We are now entering the time of year when the lake traditionally loses the most water. Rainfall is usually sparse until about the first week of June. The transition from dry to rainy is stark and sudden. Average rainfall near the lake averages about 2 inches in April to over 8 inches in June. Furthermore the sun has now risen high in the normally cloudless sky, and evaporation rates are high. A couple of weeks difference in the onset of widespread precipitation can make a big difference in Lake Okeechobee's level.
Man Made Changes to the System
The agriculture areas adjacent to Lake Okeechobee are dependent on the lake for irrigation. These agricultural interests are substantially at odds with the natural availability of water in south Florida. Rainfall is typically erratic from season to season, day to day, and even minute to minute. In the natural environment, nature has taken this into account. The Everglades is an ingenious system that deals with unpredictable rainfall.
Historically, rainfall has accumulated from inland Florida through the Kissimmee River and Lake Okeechobee into the Everglades. This filtering system slowed the flow of water to a trickle which lasted year-round and made the Everglades a 'river of grass.' There were times of less or more water, but not the wild swings that followed man's engineering of the system.
Beginning with the channelization of the Kissimmee River, engineers have changed the Everglades from a slow-flowing river to a pulsating area of water abundance and drought. After channelization, water flowed directly down the Kissimmee and the lake was inundated at times of peak rainfall. Releases from the lake, now dammed on all sides, cause water to be lost from the system through the St. Lucie canal to the ocean.
The Lake Could Dry Up Entirely
Before man's intervention in the system, the lake level was stable---higher in summer and fall, lower in winter and spring. Once the flow of water became controlled by dykes and levies, there were 2 effects: more water stands open and subject to evaporation; and water released through the canals to the sea is lost from the system. It's not surprising to find that the lake is lowering. After all, a historically stable situation where all rainfall was preserved within the system has been replaced by one in which, from time to time, water is released and lost.
Whether Lake Okeechobee will at some point dry up entirely depends on a number of factors. First there is the unpredictability of the climate, including some changes that are man-made; it is uncertain what, if any, effect global warming will have on precipitation in Florida.
Second, the engineering of the lake is slowly being changed, but the need for agricultural water remains. How the engineering is done will affect the lake level.
It seems possible that at some point there will be a drought serious enough to dry up the lake, probably not this year or next, but maybe within a decade. Unusually high levels of precipitation will at some point also likely fill the lake to capacity. Certainly some water will be retained most of the time, but the future of the lake is more in the hands of engineers than Mother Nature.
Source
- South Florida Water Management District (www.sfwmd.com), projects by region: Lake Okeechobee, Kissimmee River
- census.gov, table 358, Largest Lakes in the United States
Jon Plotkin - The author was a math major at Cornell and has a master's degree in meteorology from MIT.
