The information provided in this three-part series will be published in the future as an EDIS publication. Co-authors are: Yvette Goodiel, Paul Fisher, Robert C. Hochmuth, Ying Zhang, and Christa D. Court.

Severe weather (e.g., severe storms, tornadoes, and tropical cyclones) in Florida can damage greenhouse structures and the foods and ornamental plants being grown within them. Producers must balance the costs of structural and system upgrades against the costs of storm-related damages. Many of the considerations faced by greenhouse growers apply to other types of protected agriculture production. In this three-part series, we provide guidance to help growers plan for future storms, so they can navigate risks, mitigate impacts, recover more quickly, and build operational resiliency. In Part 1, we discuss some of the reasons growers may choose to produce within protective structures, trends in the acreage of protected agriculture, economic contributions, and storm-related losses. Here in Part 2, we describe the specific impacts that protected agriculture producers face from severe weather events in Florida. Finally, Part 3 provides guidance for growers to manage risk, mitigate impacts, and build resiliency against severe storms.

Weather-Related Impacts

Severe weather, including wind and rain, can impact greenhouse operations, compromising greenhouse structures, causing damage or loss of crops and inputs, impeding recovery efforts, and disrupting power supply.

Wind

Damaged greenhouse shown with torn plastic covering, bent metal framing, and exposed raised beds beneath. — Figure 1. Winds exert tremendous forces on greenhouse structures in Florida, especially during tropical storms, hurricanes, and tornadoes. Winds can destroy greenhouse plastic and bend the metal framing, as shown here. Growers must decide when and if to remove greenhouse coverings in advance of storms, to reduce wind loading forces acting on the frame. Credit: Y. Goodiel, UF/IFAS

The effects of wind forces acting on greenhouses are influenced by multiple factors, including wind speed, building orientation, exposed surfaces, and open areas. When wind passes over a greenhouse, it typically creates positive pressure on the windward side and negative pressure on the leeward side. This pressure difference can lead to structural issues such as collapse, warping, overturning, or uplifting effects (Figure 1). Wind speed is often converted into velocity pressure (measured in pounds per square foot, or psf), which varies as the square of the wind velocity. Depending on the shape and size of the greenhouse structure, wind can impact different surfaces. By calculating the area of each surface, the total force it must withstand can be determined. When a door or vent is left open on the windward side during high winds, the wind can pass through the opening, creating a pressure difference between the inside and the outside of the greenhouse. This can lead to a buildup of positive pressure inside the greenhouse, and as a result, the external wind can exert a stronger suction or uplift force on the structure. For example, an 80-mph wind can produce a pressure of 16 psf. For a greenhouse with a 12′ x 100′ sidewall, the total load is 19,200 pounds (Bartok, 2023). In another scenario, an 80-mph wind blowing perpendicular to the side of a 28′ x 100′ greenhouse could create a lifting force of 220 psf of length or 22,000 pounds overall. (Bartok, 2023).

Wind design loads for greenhouses in the U.S. depend on location, height, shape, and other factors. In most parts of the U.S., the basic wind speed for design purposes is 90 mph. In Florida, according to the American Society of Civil Engineers (ASCE-7), ultimate design wind speeds for risk category I buildings range from 105 to 170 mph at 33 feet above the ground in open terrain, based on a 50-year recurrence probability. Coastal areas and southern Florida are subject to higher wind speeds.

Extreme Precipitation

Vegetable production greenhouses with plastic coverings damaged by wind and ground surfaces covered in standing water after Hurricane Irma. — Figure 2. Extreme precipitation associated with Florida’s storms can flood sensitive crops and equipment within greenhouses and impede recovery efforts. Credit: Y. Goodiel, UF/IFAS

Hurricanes and tropical storms are often accompanied by heavy rains or extreme precipitation, which can result in flooding (Figure 2). Extreme precipitation and flooding can also occur during severe weather events that are not associated with a tropical cyclone. Rainfall, if impeded from draining, can weigh down plastic coverings, potentially damaging both covering and framework. Flooding can damage crops and inputs stored within the structures and impede recovery activities. For example, a 1-inch rainfall equates to 27,154 gallons of water per acre of roof area. Design rainfall should be based on the 100-year hourly rainfall rate or other approved local weather data. Typically, a 4-inch-per-hour rate is commonly used in Florida. Rates of rainfall for various cities in Florida can be found in the Florida Building Code (2023).

Power loss

Power loss can significantly disrupt greenhouse operations, especially irrigation and climate control systems.

Crop/input damage or loss

In addition to the structural damage hurricanes can bring, the heavy winds and rains can also damage crops and production materials within greenhouse structures, resulting in increased labor and material costs. Damages can be compounded by the sensitive nature of many greenhouse crops, which have been carefully cultivated in a controlled environment (Yu and Campbell 2024). Crops can remain vulnerable to storm-related damage for several months to a year after the actual storm event (Yu and Campbell 2024). Crops grown beneath greenhouse structures can be damaged when coverings are removed in preparation for the storm or when winds tear the coverings. Damage can include physical crop injury due to wind (e.g., torn leaves, pots overturned, broken branches), crop water loss due to lack of irrigation (e.g. overturned pots, broken or leaning irrigation, power loss), wind-related desiccation, excessive rainfall, leaching/runoff of crop nutrients, loss of pre-emergent herbicide from affected crops, sun damage, diseases and pests (Yu and Campbell 2024, Paul 2013). Fertilizer, pesticides, planting media, and other supplies may be damaged or contaminated by winds and rains, making these inputs unusable (Yu and Campbell 2024). After the storm, the costs of recovery may be compounded by the losses of valuable crops and inputs.

In conclusion, storm-related risks associated with greenhouse production include wind and rainfall damage to structures, crops, and equipment; loss of power supporting irrigation, ventilation, and other crop supports; and both immediate and delayed crop injury and loss. With potential risks in mind, growers and policymakers can take steps to minimize impacts and build future resiliency.

References

Bartok, J.W., Jr. 2023. “Prepare your greenhouse for weather events.” University of Connecticut Extension News and Publications. Pub #EXT038. Link no longer available.

International Code Council. 2023. Florida Building Code, Plumbing, 8^th edition. https://codes.iccsafe.org/s/FLPC2023P1/chapter-11-storm-drainage/FLPC2023P1-Ch11-Sec1106.1

Paul, Skip. 2013. “Preparing your greenhouses for a hurricane.” Umass Extension Vegetable Program. Last modified January. https://ag.umass.edu/vegetable/fact-sheets/preparing-your-greenhouses-for-hurricane.

Yu, P. and Campbell, J. 2024. “Hurricane and storm damage to greenhouse and greenhouse crops.” Temporary publication, University of Georgia Extension. Last modified October 23. https://extension.uga.edu/publications/detail.html?number=TP120.