全球气候变暖、海平面上升与日益强烈的人类活动的综合作用，导致全球海岸带区域的生态系统、环境、景观格局等发生剧烈变化，这些变化反过来又直接或间接影响着人类社会的生产与生活质量，因此受到越来越多学者、管理者与决策者的关注。海岸线的位置、走向、形态、利用方式等的时空演变不仅是海岸带景观变化的直观表现，也是区域生态环境保护、经济发展与政策导向等因素相互博弈的外在体现。因此，对于海岸线时空变化的研究，有助于海岸带环境过程及其变化机理的了解，是有效保护岸线资源、科学治理与管理海岸带环境与生态、海岸带经济与社会可持续发展的前提与基础。
 

       本研究基于遥感影像与地形图资料提取1940s、1960s、1990年、2000年、2010年与2014年六个时相的中国大陆岸线数据，在根据利用方式进行分类的基础上开展一系列研究。2010－2013年，作者所在课题组开展了覆盖整个中国大陆海岸带的野外考察，共采集GPS控制点578个，基于这些控制点对六个时相的岸线数据进行精度评估与质量控制。针对近70年来大陆岸线的时空变化特征，作者首先从海岸类型的空间分布、岸线利用方式结构、岸线分形特征、海岸带陆海格局等角度出发，揭示近70年来中国大陆岸线变化的基本特征；然后利用基于剖面计算的端点速率、线性回归速率与加权线性回归速率分析近70年来大陆岸线位置的变化趋势、不稳定性等特征；另外，参照土地利用程度综合指数与土地类型多样性指数的概念与计算方法，构建岸线利用程度综合指数与岸线类型多样性指数，多尺度分析大陆岸线开发利用程度的时空变化特征与区域岸线类型的多样性；最后聚焦9个典型区域，获取大陆岸线变化特征中具有代表性或较为特殊的区域细节。全文主要结论如下：

      1）近70年来，中国大陆自然岸线比例持续下降，至2014年已不足33%；人类活动成为岸线变化的主要影响因素，其空间规模、影响区域呈扩大化发展，强度持续增加，类型趋于多样化、人工化、均衡化与经济利益化；特别是2010年以来，人类活动的强度尤为剧烈。

      2）在1940s至2014年近70年的长时间尺度里，空间子单元除海州湾岸段以处于后退趋势的岸线为主外，其余均以处于扩张趋势的岸线为主，扩张活动主要分布于大规模连续的淤泥质海岸；近年来中国大陆海岸的后退趋势虽然因人类活动的影响而显著减弱，但各单元仍有规模可辨识的处于后退趋势的岸段，后退形式主要表现为砂砾质海岸的侵蚀后退过程。

      3）岸线利用方式的结构、岸线类型多样性、岸线分形以及海陆空间格局变化均表现出显著的空间差异性；受地形地貌影响，在杭州湾以北海岸，人口及经济活动沿海岸成面状分布，而在以南海岸则主要集中分布于大型河口三角洲地区，因此，岸线整体的位移速度、不稳定性、开发利用强度均呈现为北高南低的南北差异性格局。

      4）岸线的变化特征具有显著的时间阶段性与空间差异性：1990年以前，不稳定岸线的规模较大但扩张幅度与速度普遍不高，之后，岸线扩张幅度与速度持续增加，2010－2014年，岸线扩张幅度与速度最为显著；1990年以前，杭州湾以北岸线开发利用程度差异较显著，以南海岸差异则并不明显，而1990年以后，北方差异显著减小，南方差异则呈扩大趋势；南方重点海岸带开发区域的开发热度主要发生于1990年以前，特别是1960s－1990年间，1990年后，开发热度始终不如北方地区。

      5）1960s之前，海岸带变化的影响因素以自然过程或自然因素为主，海岸变化以自然状态淤长或侵蚀过程为主，较大规模的岸线扩张主要表现为河口岸线的自然淤长，但1960s以后，特别是1990年以后，人力作用逐渐增加并逐渐超过自然力的作用成为影响岸线变化的主导因素，海岸变化的形式则变成以养殖、港口码头、围填土地等人类活动的扩张为主。

      6）2010年以前，中国大陆海岸带开发活动的沿岸延展规模、垂直海岸的移动速率与幅度存在地区差异，即各地的开发热潮具有时间差异性；但2010－2014年间普遍具有以下特点：处于动态变化中的岸线虽然所占比例较小，但向海移动的速度与幅度为各地近70年来之最，也就是说，2010年后，全国各区域普遍进入其新的开发热潮期。

      7）20世纪40年代，全国大陆岸线的开发热点分布于长江三角洲地区，1960s以来，渤海湾及珠江三角洲地区​的岸线开发热度先后超越长江三角洲，尤其是2000年以来，渤海湾的开发热潮辐射并带动整个环渤海地区，至2014年，环渤海沿岸的开发利用程度与长江三角洲、珠江三角洲一起形成三足鼎立的格局。

       本文揭示的大陆岸线变化信息以及识别的变化热点区域，能够为海岸功能划分、开发利用规划、经济社会资源的优化配置、海岸带环境与生态系统的防治与修复提供决策和信息支持，提高决策者与管理者对岸线变化可能带来的灾害风险的重视，促进和支撑中国海岸带综合管理的实践，从而为中国海岸带的科学规划与可持续发展奠定基础。

The dramatic changes of ecological system, environment, landscape patterns in coastal area that caused by the combined effect of global warming, sea level rise, and human activities with growing intense are, directly or indirectly, affecting production and life qualities of human society, which have drawn increasing concerns from scholars, administrators and decision makers around the world. The spatio-temporal evolution of coastline position, trend, shape, utilization type, etc. not only presents changes of coastal landscape patterns, but also reflects games amongst the protection of ecological environment, economic development, and policy orientation, etc. Therefore, conducting research on spatio-temporal changes of coastline contributes to understanding coastal environmental processes and their change mechanisms, besides, it is the precondition and foundation to protect coastline resources effectively, to improve and administrate coastal environment and ecological system scientifically, and to develop economy and society in coastal area sustainably. 

 

Based on remote sensing imageries and topographic maps, six coastline positions of mainland China at 1940s, 1960s, 1990, 2000, 2010, and 2014 were extracted, subsequently, a series of studies were conducted after shorelines were categorized according to their utilization patterns. From 2010 to 2013, our research group conducted 10 field surveys that covered the whole coastal area of mainland China, as a consequence, 578 ground control points were captured and then were used to evaluate accuracies and to control qualities of six coastline positions aforementioned. As for  spatio-temporal characteristics of coastline changes in the past 70 years, the basic characteristics were revealed from the most commonly used aspects of utilization structure, fractal dimension, and spatial pattern of land and sea, and spatial distribution of coast with different kinds of substrates, etc.; afterwards, End Point Rate(EPR), Linear Regression Rate(LRR), and Weighted Linear Regression Rate(WLRR) were calculated along transects to analyze change trends and unstabilities of coastline positions in mainland China in the nearly 70 years; additionally, index of coastline utilization degree and index of coastline type diversity were constructed by referring to the concepts and calculation methods of the same indices in the field of land cover/use research; finally, by focusing on nine typical coastal subcells, representative or peculiar regional details of mainland China were delineated. The principal conclusions are as follows:

 

1) in nearly 70 years, the percentage of natural coastline in Mainland China continuously declined to 33 percent by 2014. Human activities had become the major factor that affected coastline changes, moreover, the spatial scale on which they occurred and areas they affected were in trend to broaden, the degree had a continuous trend to increase, and the categories tended to be diverse, artificialized, balanced and more inclined to be driven by economic benefits; especially after 2010, they became even more intensive;

 

2) in the long-time scale of nearly 70 years, the great majority of the coast subcells, except the coast of Haizhou bay that had a overall dominant trend to retreat, had a dominant trend to advance which mainly located at large-scale and consecutive muddy coast; in the past few years, although the retreat trend was greatly inhibited by human activities, coastlines that tended to retreat at identifiable scale could be found around the country and dominantly in the form of sandy beach erosion;

 

3) changes in coastline utilization structure, coastline type diversity, fractal dimension and spatial pattern of land and sea showed significant characteristics of spatial discrepancy and aggregation; due to differences in terrain and landform, population and economic activities stretches continuously along the coast north of Hangzhou bay, while along the coast south of Hangzhou bay, they mainly concentrated in large-scale estuary deltas, consequently, movement velocity, instability and coastline utilization degree were greater at the northern coast, presenting prominent discrepancy between north and south;

 

4) coastline changes exhibited significant phasic characteristics: before 1990, the scale of instable coastline was large while both the extent and velocity of coastline movement were generally at low level, after 1990, the extent and velocity of coastline movement increased continuously, and during the period of 2010-2014, got to the most outstanding level; before 1990, regional disparity of coastline utilization degree at the coast north of Hangzhou bay was remarkable, while the regional disparity was indistinguishable at the coast south of Hangzhou bay, however, the regional disparity significantly decreased in the northern coast while it tended to enlarge in the southern part after 1990; developing boom of major development areas at the southern coast mainly occurred before 1990, especially during the period of 1960-1990, and yet it faded and the development got to be always less thriving than that at the northern coast after 1990. 

   

5) before 1960s, natural processes and natural factors had the dominant effect on coastal changes, therefore coast changes were mainly in the form of natural accretion or natural recession, and large-scale advance of coastline was mainly in the form of natural accretion near the river mouths, but after 1960s, especially after 1990, the influence of human forces gradually increased to a certain level beyond that of natural forces, having made human activities the dominated factors that affected coastline changes, as a result, expansions of human activities, like aquaculture, harbor and wharf construction and sea reclamation, had become the dominant forms in which coast changes.

 

6) before 2010, the along-shore scale, off-shore velocity and extent of coastline development vary with regions, that is to say, there existed time lags between developing booms in different regions; however, development in different regions showed the same characteristics after 2010: the proportion of dynamic coastlines was small, however their off-shore velocity and extent reached their peak values during the period of 1940s-2014, which means, new developing booms was generally widespread around the county after 2010.

 

7) hotspots of coastline development and utilization lied in the area of Yangtze River delta at first, but since 1990s, it shifted to the coast of Tianjin and Hebei and the area of Pearl River delta, and owing to the radiant effects, development of the whole circum Bohai Sea region was accelerated, and till 2014, the coastline utilization degrees at the circum Bohai Sea region, Yangtze River delta and Pearl River delta come into being the mode of tripartite confrontation.

 

The information and hotspots of coastline changes of mainland China that were revealed and identified in this research could provide dicision-making and information support in the process of functional zoning in coastal areas, utilization and development planning, optimizing allocation of socio-economic resources, preventing and repairing the degradation of coastal environment and ecological system, and they could also rise the dicision-makers’ and administrators’ awareness of the importance of taking seriously the potential hazard risk that coastline changes may cause, as well as promote and support the practices of coastal integrated management in China, consequentially, lay the foundation for scientific planning and sustainable progressing in coastal areas of mainland China.