Automated High-Resolution Time Series Mapping of Mangrove Forests Damaged by Hurricane Irma in Southwest Florida

Matthew J. McCarthy,Marissa Figueroa,Brita Jessen,Jessica McIntosh,Tylar Murray,Frank E. Muller-Karger,Michael J. Barry,Jill Schmid

doi:10.3390/rs12111740

Abstract

In September of 2017, Hurricane Irma made landfall within the Rookery Bay National Estuarine Research Reserve of southwest Florida (USA) as a category 3 storm with winds in excess of 200 km h−1. We mapped the extent of the hurricane’s impact on coastal land cover with a seasonal time series of satellite imagery. Very high-resolution (i.e., <5 m pixel) satellite imagery has proven effective to map wetland ecosystems, but challenges in data acquisition and storage, algorithm training, and image processing have prevented large-scale and time-series mapping of these data. We describe our approach to address these issues to evaluate Rookery Bay ecosystem damage and recovery using 91 WorldView-2 satellite images collected between 2010 and 2018 mapped using automated techniques and validated with a field campaign. Land cover was classified seasonally at 2 m resolution (i.e., healthy mangrove, degraded mangrove, upland, soil, and water) with an overall accuracy of 82%. Digital change detection methods show that hurricane-related degradation was 17% of mangrove forest (~5 km2). Approximately 35% (1.7 km2) of this loss recovered one year after Hurricane Irma. The approach completed the mapping approximately 200 times faster than existing methods, illustrating the ease with which regional high-resolution mapping may be accomplished efficiently.

Highlights

Up to 71% of global wetlands have been lost to anthropogenic development during the 20th century, and are expected to continue to decline at a rate of 1%–3% annually [1,2]
We describe the results of a project to map and monitor mangrove forest change from 2010 to 2018 using 91 high-resolution WorldView-2 satellite images
We evaluate changes as a result of chronic stress owing to sea-level rise or hydrologic alteration, as well as those resulting from Hurricane Irma, a category 3 storm that made landfall within the study area in September of 2017

Summary

Introduction

Up to 71% of global wetlands have been lost to anthropogenic development (e.g., construction, wetland drainage, hydrologic alterations) during the 20th century, and are expected to continue to decline at a rate of 1%–3% annually [1,2]. Recent research suggests that better understanding and monitoring of wetland extent is needed to fill vital knowledge gaps in understanding global greenhouse gas emissions [8,9] Filling these gaps and enhancing management capabilities to manage coastal wetland habitats require accurate and up-to date information on wetland area; habitat composition; biomass and carbon stock; and impacts of stresses such as development, sea level, and temperature changes associated with climate change and severe storms [10,11]. This requires rapid repeat monitoring of coastal habitats at very high spatial resolutions to facilitate local detection of change before it expands beyond the capacity of existing conservation and restoration methods

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