Tropical Cyclone Impact and Forest Resilience in the Southwestern Pacific

Baptiste Delaporte,Marc Despinoy,Christophe Menkes,Morgan Mangeas,Thomas Ibanez

doi:10.3390/rs14051245

Abstract

Tropical cyclones (TCs) can have profound effects on the dynamics of forest vegetation that need to be better understood. Here, we analysed changes in forest vegetation induced by TCs using the normalized difference vegetation index (NDVI). We used an accurate historical database of TC tracks and intensities, together with the Willoughby cyclone model to reconstruct the 2D surface wind speed structure of TCs and analyse how TCs affect forest vegetation. We used segmented linear models to identify significant breakpoints in the relationship between the reconstructed maximum sustained wind speed (Wmax) and the observed changes in NDVI. We tested the hypothesis that the rate of change in damage caused by TCs to forest and recovery time would increase according to Wmax thresholds as defined in the widely used Saffir–Simpson hurricane wind scale (SSHWS). We showed that the most significant breakpoint was located at 50 m/s. This breakpoint corresponds to the transition between categories 2 and 3 TCs in the SSHWS. Below this breakpoint, damages caused to forest vegetation and the time needed to recover from these damages were negligable. We found a second breakpoint, with a sharp increase in damages for winds >75 m/s. This suggested that extremely intense tropical cyclones, which might be more frequent in the future, can cause extreme damages to forest vegetation. Nevertheless, we found high variation in the observed damages and time needed to recover for a given Wmax. Further studies are needed to integrate other factors that might affect the exposure and resistance to TCs as well as forests’ capacity to recover from these disturbances.

Highlights

Tropical cyclones (TCs), referred to as hurricanes in the North Atlantic and Northeast Pacific and typhoons in the Northwest Pacific, generate high speed winds and heavy rainfalls over large areas
We found that damages caused to forest vegetation by TCs based on normalized difference vegetation index (NDVI) changes were negligible for winds
Reduction in NDVI increased linearly with increasing wind speed which likely resulted from increasing major damages to vegetation, including branch breaking, tree uprooting, and bole snapping

Summary

Introduction

Tropical cyclones (TCs), referred to as hurricanes in the North Atlantic and Northeast Pacific and typhoons in the Northwest Pacific, generate high speed winds and heavy rainfalls over large areas. Immediate impacts of TCs on forests can be devastating with damages ranging from defoliation to extensive trunk snapping or tree uprooting. Most studies focused on the local- or landscape–scale damages caused by a single TC (e.g., [1–9]). Analyses of the impacts of multiple TCs on larger regional or global scales are needed to better understand how forests respond to these large–scale disturbances in the context of changing TCs intensity [10]. Available and accurate remote–sensed vegetation index time series and TC trajectories and characteristics databases allow to analyse the impacts of TCs on forests and their recovery at large spatio–temporal scales (e.g., [11–13]).

Methods

Results

Discussion

Conclusion