Abstract
The South China Sea is currently in a state of intense geopolitical conflict, with six countries claiming sovereignty over some or all of the area. Recently, several countries have carried out island building projects in the Spratly Islands, converting portions of coral reefs into artificial islands. Aerial photography and high resolution satellites can capture snapshots of this construction, but such data are lacking in temporal resolution and spatial scope. In contrast, lower resolution satellite sensors with regular repeat sampling allow for more rigorous assessment and monitoring of changes to the reefs and surrounding areas. Using Landsat-8 data at ≥15-m resolution, we estimated that over 15 km2 of submerged coral reef area was converted to artificial islands between June 2013 and December 2015, mostly by China. MODIS data at ≥250-m resolution were used to locate previously underreported island building activities, as well as to assess resulting in-water turbidity plumes. The combined spatial extent of observed turbidity plumes for island building activities at Mischief, Subi, and Fiery Cross Reefs was over 4,300 km2, although nearly 40% of this area was only affected once. Together, these activities represent widespread damage to coral ecosystems through physical burial as well as indirect turbidity effects.
Highlights
The Spratly Islands are a large archipelago of coral reefs and islands in the South China Sea (SCS, Fig. 1)
The slope of Moderate Resolution Imaging Spectroradiometer (MODIS)/A Rayleigh-corrected reflectance (Rrc)(859) at each pixel was used to identify the pixels which had likely changed from water to land targets, with higher slope values indicating artificial island creation
Note that Spratly Island lies outside the bounds of the MODIS/A data used in this analysis
Summary
The Spratly Islands are a large archipelago of coral reefs and islands in the South China Sea (SCS, Fig. 1). As a consequence of the geopolitical tensions, there is sustained interest in detecting and monitoring changes in the region Among such changes, several countries (especially China and Vietnam) have recently embarked on island building activities in the region, converting all or part of several submerged coral reefs into artificial islands (Fig. 1). Compared to aerial photography and commercial satellite data, the high temporal resolution and wide swath of MODIS/A and OLI increase the ability to detect and monitor island building activities and resulting environmental changes. The overall goal of this work was to use OLI and MODIS/A data to identify and assess changes in the Spratly Islands region of the South China Sea, with specific objectives to (1) identify reef locations converted to artificial islands and document their size, and (2) quantify effects of island building activities on water turbidity
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