SHANGHAI SHORELINE EVOLUTION INTERPRETED FROM HISTORICAL ATLAS AND REMOTE SENSING IMAGERY OVER THE PAST 2,200 YEARS

Abstract. Shanghai, the axis of economic development in China and holding the most prosperous metropolis in the world, is located at Yangtze Estuary which is susceptible to shoreline changes affected by different factors, such as sediment supply and sea level changes, making it very important to study the shoreline changes over long time period. This paper presents the Shanghai shoreline evolution process from BC 221 up to 2015, by employing both the cartographic data (historical atlas) and the remote sensing images. A series of image processing techniques were applied to seamlessly register the historical atlas and satellite images to the same orthophoto base map, followed by the semi-automatic extraction of shoreline from images. Results show that since BC 221, the Shanghai shoreline has been witnessing distinct progradation, and the rate of shoreline advance varied in different areas. The average shoreline change in southern Yangtze Estuary was about 2,573 km² (accretion) between BC 221 and 1948 with a 40 km progradation, while the shoreline in northern Hangzhou Bay kept relatively steady after 1671. Overall, 3,119 km² of Shanghai area was added between BC 221 and 1948 with an average rate of 75 km²/50yr, and the addition went to 4,372 km² in 2015. In this paper, the possible drives of the shoreline evolution was discussed. This study is important for understanding the coastal dynamics in Shanghai over a long time period for the management and development of coastal environments.