High impact freezes have been rare events scattered unevenly through the century: Dec '62, Dec '83, Jan '85 and Dec '89. If one adds near impact freezes on Dec '34, Jan '40, Jan '77, Jan '81, and Jan '82 to the list and spreads them evenly over the century there are fewer than one per decade. But they are clustered in time. There was a clump in the 1890's, and certainly there was a cluster in the 1980's. These clumps of freezes show up clearly in graphs of citrus yield versus time. Following each of these clumps of freezes, the center of the industry moved southward. The Florida State Horticultural Society helped initiate the Federal-State Frost Warning Service in 1935, which had a long and productive history until its end in 1996. Growers used cultural practices, site selection, wood, and later oil fueled fires, wind machines, and various irrigation practices to protect their trees from cold damage. A few experimented with grove covers, wind breaks, combinations (e.g., heated irrigation), but the tendency was to ignore the remote possibility. Networking thermometer readings, the advent of electronic communications, automated weather stations, and thermal maps from satellite images have helped growers pick sites least likely to be as cold as other sites during freezes. Even though freezes have common characteristics, they are also unique in other ways. The hope that most events would be radiative in nature (clear, calm, and dry) was dashed, but undertree sprinklers added protection even in advective freezes. There can be little hope Global Warming will decrease the number or the severity of Florida Freezes. Quite the contrary, for some predict that both the frequency and the severity will increase as Global Warming becomes more apparent. The experience of the past century suggests growers will continue to tell themselves that freezes are extremely unusual, especially in South Florida. The responsibility for turning on the irrigation system is likely to be delegated more and more often. The key seems to be in knowing when the rare event could have a distinct possibility of happening. FAWN, and perhaps DISC, show promise in this regard.


cold protection; frost warning; weather; climate; rare events; information systems

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283