Analysis Of Spatio-temporal Characteristics Of Mainland Coastline Changes In China In Nearly 70 Years

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 1940 s, 1960 s, 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 adominant 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 1960 s, 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 1960 s, 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 1990 s, it shifted to the coast of Tianjin and Hebei and thearea 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.