Abstract: China has experienced several booms in sea reclamation since the mid-20th century. The reclamation in Bohai Rim expanded dramatically in a scale much larger than in other coastal zones in China, especially since 2 000. Therefore, based on topographic maps, nautical charts, and multi-temporal remote sensing imageries, the two-dimensional centroid, three-dimensional centroid, shoreline, low tide line, depth contour, bay area, and water volume of Bohai Sea since the 1940s were extracted and analyzed to reveal the tendencies, characters, and driving factors of long-term shape changes of Bohai Sea. The results indicate that, during the past 70 years, the area of Bohai Sea decreased continuously and that shoreline, low tide line, and 5 m isobaths shifted toward the sea in most coastal areas. Consequently, the two-dimensional centroid of Bohai Sea moved northeastward significantly, while the perimeter increased remarkably and the geometric shape became complicated. During the past 50 years, overall, the volume of Bohai Sea declined and the three-dimensional centroid dived significantly. The development of estuary delta and sea reclamation were the fundamental driving forces of long-term shape changes of Bohai Sea. However, the human forces have gradually exceeded the natural forces.

Key words: Bohai Sea, shoreline, depth contours, DEM (digital elevation model), centroid, shape character