Abstract
The evolution of estuarine islands is potentially controlled by sediment discharge, tidal currents, sea level rise, and intensive human activities. An understanding of the spatial and temporal changes of estuarine islands is needed for environmental change monitoring and assessment in estuarine and coastal areas. Such information can also help us better understand how estuarine islands respond to sea level rise in the context of global warming. The temporal changes of two estuarine islands in Shanghai near the Yangtze River Estuary were obtained using Landsat TM (Thematic Mapper) and ETM+ (Enhanced Thematic Mapper) images from 1987 to 2016 on an annual scale. First, a composite image was generated by using the multi-temporal Landsat images for each year. Then, a modified normalized difference water index (MNDWI) was applied to the annual estuarine island maps using a threshold segmentation method. Finally, we obtained the temporal changes of the estuarine islands in Shanghai during the period 1987–2016. The results suggest that (1) Landsat TM/ETM+ images can be used for estuarine island mapping and change detection; (2) the two estuarine islands have expanded significantly during the past three decades; (3) human activities are the main driving factor that caused the expansion of the estuarine islands; and (4) the sea level can also partly explain the change in the estuarine islands. This study demonstrates that Landsat data are useful for determining the annual variations in the land area of two estuarine islands in Shanghai during the past 30 years. In the future, other factors and their contributions to estuarine island changes should be further investigated.
Highlights
The evolution of estuarine islands can be shaped by sediment discharge, sea level rise, and tidal currents [1,2]
Landsat Thematic Mapper (TM)/ETM+ images can be used for estuarine island mapping and change detection; (2) the two estuarine islands have expanded significantly during the past three decades; (3) human activities are the main driving factor that caused the expansion of the estuarine islands; and (4) the sea level can partly explain the change in the estuarine islands
The annual-scale temporal changes of two estuarine islands, which are located in Shanghai near the Yangtze River Estuary, were obtained from Landsat (TM and ETM+) data for the period of 1987–2016 based on Google Earth Engine and MATLAB
Summary
The evolution of estuarine islands can be shaped by sediment discharge, sea level rise, and tidal currents [1,2]. Intensive human activities near coastal areas can greatly change the morphologies of estuarine islands by the process of land reclamation [3,4,5]. Such coastal projects are common in coastal zones, in coastal China, which has experienced rapid economic development since. Changxing Island and Hengsha Island are the second and third largest islands in Shanghai, which serves port, coastal industry, high-end service, and tourism functions. Because of intensive human activities around the two islands [12], timely and accurate information on the temporal changes of estuarine islands is
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