Assessment of ecological disturbance in the mangrove forest of Sundarbans caused by cyclones using MODIS time-series data (2001–2011)

Abstract

The mangrove ecosystem of Sundarbans region plays an important ecological and socioeconomical role in both India and Bangladesh. The satellite-based approach has been adopted for assessing the ecological disturbance caused by major cyclones. Moderate Resolution Imaging Spectroradiometer (MODIS) time-series (2001–2011) Enhanced Vegetation Index (EVI) and Land Surface Temperature (LST) products were used to compute the MODIS Global Disturbance Index (MGDI). The pre- and post-cyclonic changes in the EVI as well as LST were analyzed to study the impact of cyclones on the vegetation and surface temperature, respectively. In the present study, time-series MGDI was transformed to the percentage change in MGDI using temporal mean for each pixel, and its response toward cyclonic events was studied. The pre- and post-cyclonic Landsat data were analyzed to identify the affected areas discernible on the image and a threshold was decided to mark the “disturbed pixels.” The threshold for the instantaneous disturbance caused by cyclones was found to be more than 11 % of the temporal mean MGDI. The selected threshold was applied on the time-series MGDI images to delineate the disturbed pixels, and percent-disturbed area of each Island was computed. The classified disturbed area maps were able to characterize the impact of cyclones and effectively represent the distribution of the spatial intensity of the ecological disturbance in Sundarbans region.