Vegetation activity monitoring as an indicator of eco-hydrological impacts of extreme events in the southeastern USA

Abstract

A vegetation disturbance persistence metric based on Moderate-Resolution Imaging Spectroradiometer North American Carbon Program vegetation indices (8-day composite at 500 m spatial resolution) was developed with the objective of assessing the eco-hydrological impact of extreme events generally, and hurricanes and tropical cyclones in particular, in the southeastern USA. The metric is based on the relationship between vegetation stress and the persistence of standardized enhanced vegetation index anomalies. The data show that in the first water year (October–September) after hurricane landfall, pronounced decreases in chlorophyll activity are found predominantly at very low elevations – including coastal marshes, wetlands, and the floodplains aligned with drainage networks of major river systems along the storm track. Inland impacts are mainly located in agricultural areas and woody wetlands in the floodplains, and in forested headwater basins in the mountains. Overall, the data analysis indicates that the major impacts of these storms are on agricultural and natural land-margin ecosystems predominantly via flooding associated with the storm surge along the coast, and flood propagation through the river networks inland. The timescale of impacts in coastal areas is up to two years, consistent with persistent impacts of salt intrusion in shallow coastal aquifers, erosion of root zone soils, and depletion of nutrients due to flooding. By contrast, ecological drought disturbance patterns exhibit larger spatial persistence but significantly shorter timescales (3–4 months).

Acknowledgements

This research was supported in part by a NASA Earth and Space Science Fellowship with the first author and by NOAA SARP-WATER grant NA08OAR4310701. The authors thank the anonymous reviewers for their constructive comments and suggestions. The authors are grateful to Dr Jeffrey T. Morisette for guidance on the MODIS NACP phenologically corrected products. They also acknowledge Dr Denis Jacobs for the information provided on the impacts of hurricanes Ivan and Katrina on forested areas in southeastern USA.