Long-term Temperatures and Cold Event Return Intervals in the Dover/Plant City Water Use Caution Area

Periodic freezing temperatures in west-central Florida are a naturally occurring seasonal weather pattern that can cause substantial economic impacts to agriculture and residents. During prolonged freezes, agricultural growers risk losses of certain crops. To lower the likelihood of damage, surface water or groundwater can be used for cold protection of crops, although groundwater is preferred because of its relatively consistent lukewarm temperature and lower potential for pathogens. Cold protection for many crops in this region is typically initiated when temperatures fall at or below 34° F. In 2010, nine nights of freezing or near-freezing temperatures occurred over 11 consecutive days from January 3 to 13 in the Dover/Plant City area of eastern Hillsborough County, Florida. The event was record-breaking in many parts of central and southern Florida. At the beginning of 2010, permitted average annual water use in what is now the Dover/Plant City Water Use Caution Area was 157 million gallons per day (mgd). During the 2010 cold event, an estimated 891 mgd was extracted for cold protection in the DPWUCA. Groundwater modeling showed that drawdown in the Upper Floridan aquifer could have exceeded 80 feet at the cone of depression's center, while drawdown greater than 5 feet extended over an area of about 222 mi². Approximately 760 dry well complaints and 140 documented sinkholes occurred near the area of maximum drawdown. This technical memorandum attempts to place the 2010 event in context by analyzing long-term temperature data for the area and estimating a recurrence interval for an event of similar magnitude. Additionally, cold event durations (in hours) and starting groundwater level elevations are assessed.