sustainability Article Analysis and Prediction of Changes in Coastline Morphology in the Bohai Sea, China, Using Remote Sensing Ying Fu 1, Qiaozhen Guo 1,*, Xiaoxu Wu 2, Hui Fang 2 and Yingyang Pan 1 1 School of Geology and Geomatics, Tianjin Chengjian University, Jinjing Road, Tianjin 300384, China; [email protected] (Y.F.); [email protected] (Y.P.) 2 College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China; [email protected] (X.W.); [email protected] (H.F.) * Correspondence: [email protected]; Tel.: +86-22-2377-3133 Academic Editor: Vincenzo Torretta Received: 1 April 2017; Accepted: 22 May 2017; Published: 29 May 2017 Abstract: Coastline change reflects the dynamics of natural processes and human activity, and influences the ecology and environment of the coastal strip. This study researched the change in coastline and sea area of the Bohai Sea, China, over a 30-year period using Landsat TM and OLI remote sensing data. The total change in coastline length, sea area, and the centroid of the sea surface were quantified. Variations in the coastline morphology were measured using four shape indexes: fractal dimension, compact ratio, circularity, and square degree. Equations describing fit of the shape index, coastline length, and marine area were built. Then the marine area 10 years later was predicted using the model that had the highest prediction accuracy. The results showed that the highest prediction accuracy for the coastline length was obtained using a compound function. When a cubic function was used to predict the compact ratio, then the highest prediction accuracy was obtained using this compact ratio and a quadratic function to predict sea area. This study can provide theoretical support for the coastal development planning and ecological environment protection around the Bohai Sea. Keywords: coastline change; shape index; fitting; prediction 1. Introduction Coastline is physical interface of land and ocean. Changes in coastline occur for two main reasons: natural processes and human factors. Cities and populations in coastal areas have increased rapidly due to abundant natural resources, leading to numerous development projects. Coastal development has brought prosperity to society but also has led to coastal hazards such as erosion by the sea, sea water intrusion, coral bleaching, and coastline change [1]. Coastline change in turn affects coastal ecological environment and economic development and wellbeing of communities. Coastline change reflects modification of the natural environment and influence of human activities in coastal areas, so research on the spatial and temporal patterns of coastline change is of great significance. Wavelet analysis was extremely useful as a tool for analyzing coastal data and for data-driven modelling. However, there are still limits in scales, space, and time to its use [2,3]. Remote sensing has characteristics of broad scale, rapid, and real-time collection, which can capture environmental dynamics in many situations. Using remote sensing to analyze coastline changes can provide dynamic, scientific, timely, and valid information for relevant decision-making departments, and can assist with not only development and use of the coast as well as tidal flats but also with disaster evaluation of the ocean. At present, remote sensing is the main method of monitoring coastline changes [4,5]. Sustainability 2017, 9, 900; doi:10.3390/su9060900 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 900 2 of 14 Al-Hatrushi monitored the coastline change of the Al Hawasnah tidal inlet on the Al Batinah coast of the Sultanate of Oman using remote sensing and GIS [6]. Deepika et al. estimated and forecasted the rate of coastline change using remote sensing [7], while Zhang et al. evaluated coastline changes due to human intervention in the Zhoushan Islands of China [8]. Landsat TM and OLI remote sensing data are often used in the study of coastlines because it is easily obtained and has a long temporal coverage. For example, Bouchahma and Yan used eight Landsat TM images to develop an approach to measure, analyze, and model the coastline, then predict and manage the changes in the coastal environment [9]. Kankara et al. estimated long and short term coastline changes along Andhra Pradesh coast using TM remote sensing images [10]. Cui et al. studied the coastal landform, coastline, and erosion of geomorphic silt in Laizhou Bay over the past 30 years using TM and OLI data [11]. Wu et al. used multi-year TM and OLI images to analyze temporal and spatial variation and driving forces of coastline change in Yueqing Bay [12]. The Bohai Sea plays an important role in China, including in the fields of energy production, environment protection, and economic development. Most studies to date have examined parts of the Bohai Sea coast, but few have carried out a comprehensive analysis of the whole Bohai Sea. For example, Li et al. studied the temporal and spatial variation of the coastline and coastal zone of the Bohai Bay in five key research areas [13]. Zhang et al. studied the evolution of coastline and tidal flats of the western and southern parts of the Bohai Bay from 1975 to 2010 and identified factors that affected these changes [14]. Sun et al. studied the location, length, and structure of the Bohai Bay coastline from 2000 to 2010, carried out a quantitative inversion of the space-time change process of the coastline, and analyzed its causes [15]. Zhang et al. extracted and monitored coastline change in the Qinhuangdao City [16]. Wang et al. researched the process of morphological changes in coastline and near-shore marine areas on two sides of the Port of Huanghua [17]. Broadly, the instantaneous water line is the direct boundary between ocean and land, thus it can be considered to be the shoreline. At present, the shoreline is generally replaced by water edge of the imaging time when monitoring the change of coastline using remote sensing [18]. The coastline extraction methods are generally divided into automatic extraction, semi-automatic extraction, and visual interpretation. Image noise and resolution factor will influence the continuity and correctness of coastline when using automatic and semi-automatic extraction methods, as such, the extraction results need to be modified by artificial auxiliary [19]. Unified interpretation signs shall be established according to different coastline types and a comparatively accurate result can be obtained using a visual interpretation method. This method is suitable for research of large-scale shoreline change, for example, Miao et al. used the visual interpretation method to extract coastline in the Tumen River estuary and adjacent areas and monitor its change of nearly 30 years [20]. Zhang used the visual interpretation method to obtain such information as location, length, and type of Zhuhai coastline and did detailed analysis and research on the change of coastline between 2004 and 2014 [21]. Liao et al. extracted coastline information of Zhejiang province using the visual interpretation method and analyzed the spatial and temporal variation characteristics [22]. This paper aims to study the basic situation, change rule, and trend of the Bohai Sea coastline. It can meet the research requirements to regard the instantaneous water edge as the coastline. The coastline was divided into artificial coast, bedrock coast, sandy coast, and muddy coast according to remote sensing image information and the actual situation. The coastline was extracted using the visual interpretation method based on establishing various interpretation signs of different types of coastlines. The length of the coastline, sea area and the change of the centroid of the Bohai Sea were obtained for four years (1985, 1995, 2005, and 2015). The changes in the coastlines of three adjacent coastal provinces, one city, and 46 counties over the 30-year period were analyzed. The changes in coastline morphology were studied using four shape indexes: fractal dimension, compact ratio, circularity, and square degree. The best fitting models for each shape index in relation to coastline length, and between each shape index and the year were built by comparing the coefficients of determination. The fitting models for compact ratio, circularity, and square degree in relation to Sustainability 2017, 9, 900 3 of 14 coastline length were hardly mentioned in the previous studies. Finally, the scheme used to forecast changes in the coastline and sea area in the next 10-year period was built, and an evaluation of the Sustainability 2017, 9, 900 3 of 14 forecasted results was carried out. changes in the coastline and sea area in the next 10-year period was built, and an evaluation of the 2. Studyforecasted Area andresults Data was carried out. The Bohai Sea is located at 37◦270–41◦00N, 117◦350–121◦100E[23] (Figure1). The eastern end of 2. Study Area and Data the Bohai Sea and Yellow Sea are linked by the Bohai straits. The Bohai Sea has a variety of marine species, andThe is Bohai used Sea to provideis located five at 37°27 economic′–41°0 resources:′N, 117°35′–121°10 fishing,′E ports,[23] (Figure oil, tourism, 1). The andeastern sea end salt. of It has experiencedthe Bohai pollution Sea and Yellow from theSea are land linked and by oil the spills. BohaiIn straits. recent The years, Bohai withSea has rapid a variety economic of marine growth, species, and is used to provide five economic resources: fishing, ports, oil, tourism, and sea salt. It the Circum-Bohai Sea Economic Zone has become one of the most important areas for economic has experienced pollution from the land and oil spills. In recent years, with rapid economic growth, developmentthe Circum-Bohai in China Sea after Economic the Pearl Zone River hasdelta become and one the of Yangtze the most River important delta areas [24].