LCMAP Change Stories: Hurricanes in the Everglades

Science Center Objects

When Atlantic hurricanes make landfall in south Florida, the coastal marshes and mangrove forests of the Everglades often act as a buffer that protects residents from rising sea levels, high winds and storm surge.

Animation of Land Change in Florida Everglades, 2005

Animation of land change in Florida's Everglades in 2005, created using Landsat imagery and three USGS Land Change Monitoring, Assessment, and Projection (LCMAP) products.

In serving that protective function, however, the Everglades wetlands ecosystems can sustain severe damage. Hurricane-force winds can strip trees of leaves and limbs or fell them entirely. Churning storm surge and the sediment deposits left behind can suffocate tree roots and slow post-storm recovery.

The Everglades have borne the brunt of multiple significant hurricane events since the early 1990s, including Hurricane Andrew in 1992, Hurricanes Katrina and Wilma in 2005, and Hurricane Irma in 2017.

Data from the USGS Land Change Monitoring, Assessment, and Projection (LCMAP) initiative offer new insight on the extent of the disturbance caused by those events.

These graphics show land surface change in south Florida, estimated using the Continuous Change Detection and Classification (CCDC) algorithm and Landsat source data. They are notable not only for what they show, but for what they do not. These data estimate both the day of the year upon which impacts were initially detected in the Landsat record and the spatial area of those impacts. In these cases, change in the Everglades due to hurricane events do not alter the wetlands land cover categorization.

The CCDC approach can capture and quantify landscape disruptions caused by individual hurricane events on a broad scale – in some cases amounting to 10 percent of the Everglades National Park

The hurricane findings underscore a significant benefit to this approach: The ability to characterize and study ephemeral landscape change within a single calendar year, across more than three decades of the Landsat record.

1992 - Hurricane Andrew

Image showing land cover change products in south Florida for 1992

Hurricane Andrew formed over the Atlantic on Aug. 16, 1992 and made landfall in south Florida eight days later as a Category 5 storm, causing significant damage to vegetation in Everglades National Park. Perhaps the most dramatic effect of its passage through these wetlands was the major structural damage to trees, caused by strong winds.

Andrew passed directly over Biscayne and Everglades National Parks, knocking down or severely damaging mangroves across about 28,000 hectares of wetlands across Florida and Louisiana, according to a summary from the USGS.

The year 1992 was a busy hurricane year, and the LCMAP Change Day product captured significant landscape change on several days throughout the year, changes that generally fall close to the date of a non-hurricane event. Even so, the impact of Andrew was notable. The date with the greatest number of changed pixels was tagged to Sept. 2 – spectral changes most clearly attributable to Hurricane Andrew.

Adding up spectral changes the Landsat record for the 25 days following Andrew’s arrival in Florida amounts to an estimated 152 square kilometers of disruption. The assessment highlights the ability of LCMAP products to pinpoint change from specific events.

 

2005 - Hurricanes Katrina and Wilma

Image showing land cover change map products in south Florida for 2005

 

Image: Mangroves Killed by Hurricane Wilma in Everglades National Park

Shark Island, Everglades National Park, where numerous mangroves were killed by high winds and storm surge from Hurricane Wilma.

LCMAP products offer evidence of massive change in the Everglades in 2005 when several major hurricanes passed over, although years with multiple hurricanes creates additional complexity for change assessments.

Hurricane Katrina developed on Aug. 23 and made landfall two days later, striking the east side of the state as a category 1 storm between Broward and Miami-Dade counties, then losing force as it moved southwest across Florida. Katrina dropped 25.4 centimeters (10 inches) of rain on the Florida Keys, and tides in the Everglades reached 1 to 1.5 meters (3-5 feet) in some areas. The park saw shoreline erosion, floating and submerged debris, as well as a shifting of bottom sands.

Hurricane Wilma struck late in the hurricane season. After forming over the Caribbean and crossing over the tip of the Yucatan, Hurricane Wilma arrived in southwest Florida on Oct. 24. Storm surge swept into coastal areas as it moved northwest, and the Everglades were particularly hard hit. Initial wind speeds of 120 miles per hour were recorded near Naples, FL, causing significant damage to the power grid.

LCMAP products offer evidence of massive change in the Everglades in 2005, although a multiple hurricane year creates additional complexity for change assessments.

The Change Day product marks the first day of the year in which a spectral change in the Landsat record is detected as a change event, but Katrina and Wilma’s overlapping areas of impact make it difficult to separate the damage done by each individual storm. Viewed in the context of each storm’s path, the data offer spatial clues.

Inland change is marked as occurring on Aug. 28, shortly after Katrina. Much of the coastal area that saw impacts from both storms are marked as changing on either Nov. 1 or Nov. 8. Given those caveats, the Change Day product pins approximately 60 square kilometers of disturbance to the Everglades to Katrina and 364 square kilometers to Wilma.

The addition of a rapid change detection capability could mean a quicker and possibly more detailed analysis of breaks in the Landsat time series in years impacted by multiple events.

 

2017 - Hurricane Irma

Image showing land cover change products in south Florida for 2017

A thin band of dead mangroves are are all that remain on one side of a playa after Hurricane Irma hit Florida

Mangroves in Florida Bay, shown after Hurricane Irma.

The most recent hurricane to strike the Everglades formed off the coast of the Africa’s Cape Verde islands on Aug. 30, 2017.

Hurricane Irma was an especially strong and lengthy event, making landfall as a Category 4 storm in Monroe County, FL on Sept. 10 and moving north through Florida and Georgia.

The Florida Keys were the hardest hit area in state, battered by strong sustained winds of up to 180 kilometers per hour and approximately three meters of storm surge, accompanied by heavy precipitation and flooding. Gusts of more than 225 kilometers an hour did extensive damage to the forest canopy.

The Change Day product detected 378 square kilometers of disruption to Everglades National Park following Hurricane Irma, with the largest spike in spectral change on Sept. 17, 2017.

Using the CCDC approach, the USGS EROS is producing a 33 year history of land change information for the conterminous U.S.  

For more information on the LCMAP product suite, click here.

To download LMCAP sample data, visit this page.