Research On Spatial And Temporal Characteristics Of Island Coastline Along The Maritime Silk Road

Coastline is an important geographical element of the boundary between sea and land,and has important ecological function and resource value,which is the front position of developing Marine economy.The geographic and morphological characteristics and evolution rules of the coastline are unique.Its length,location,form and dynamic changes are the results of the combined effects of macro-scale climate change and land-sea interactions,regional-scale estuaries and coastal environmental processes,and multi-scale human activities.It not only reflects the environmental characteristics and evolution trend of the coastal zone,but also reflects the complex and dynamic gambling relations between the economic and social development of the coastal zone,the changes of ecological environment and policy orientation.Therefore,coastline distribution and dynamic change monitoring research constitutes the basis of coastal regional environmental monitoring,resource development and management,and ecosystem protection.Strengthening coastline dynamic monitoring and research will not only help promote the scientific cognition on coastal zone environment and ecological process.It is able to support scientific and reasonable land-sea overall decision and promote the sustainable management,development and protection of coastal resources,environment and ecosystems.Island coastlines are undergoing drastic changes,erosion or expansion,under the background of the global climate change and high-intensity human intervention.Especially,the island has increasingly become a hot topic of concern by the government,scholars and media,against the context of accelerating sea level rise(SLR).And there are more and more arguments about the long-term situation of the form and position of the island coastline.However,there are few researches on the characteristics and laws of island coastline evolution at large spatial and temporal scales.Therefore,the incomplete understanding of the characteristics of island coastline change and the lack of high-quality data are a deficiency of current researches.On the other hand,China put forward the strategic conception of the 21st Century Maritime Silk Road in 2013.The islands along the route have an important strategic position.Mastering the evolution process of the islands and coastlines is of great significance to the strategic development of the 21st Century Maritime Silk Road and the sustainable development and management of islands along the route.The main contents of this study include:(1)Establishing a classification system for islands and coastlines in the Maritime Silk Road area;(2)Built a database of data sources of coastline extraction,including Landsat TM/ETM+/OLI,global LUCC data,Google Earth images,world atlases,etc.;(3)Established detailed coastline interpretation standards and technical procedures;(4)Built island coastline data set including basic information of island and coastline though manual visual interpretation;(5)Based on mathematical statistics,geospatial analysis,correlation analysis and other theories and methods,analyzed the spatial and temporal dynamic changes of islands and coastlines from multiple angles and scales quantitatively,including island distribution,island area,island location,island shape,coastline length and structure,coastline spatial position,and changes of land-sea pattern of islands.(6)Through multi-source data,combining with hot spots,the influencing factors of coastline change were discussed and analyzed in detail from the perspectives of natural and human activities,and the specific driving factors of coastline change were elaborated in hot spots.Based on the above work,a relatively complete island coastline research system has been established,drawing the following main conclusions:(1)This study extracted 12,737,13,542,and 13,633 islands in 1990,2000,and2015,respectively.Small islands(<10 km~2),bedrock islands,and coral islands were widely distributed.The island coastline lengths are respectively 196,600 km,198,900km and 199,900 km,showing an overall increasing trend,while the natural coastline lengths and artificial coastline lengths shows a decreasing and increasing trend respectively.The artificial rate of coastline and the degree of development and utilization of coastline both are at a low level.(2)In the past 25 years,the coastline of islands in this study area is mainly in a stable state,and the proportion of unchanged coastline is as high as 88%.The length of the coastline with changes in spatial location is about 24,200 km,accounting for12.31%,of which 7.61%is in the state of receding land and 4.70%belong to the state of seaward advancement.The erosion area caused by coastline retreat is about 2488km~2 and the new area caused by the coastline expansion is about 2023 km~2.(3)There are obvious temporal and spatial differences in island form and coastline changes,which are reflected in different spatial scales.For example,on large spatial scale,the coastline changes of Southeast Asian archipelagoes are obviously stronger than those in South-Western Asia and the Mediterranean.On regional scale,the Indonesian archipelago of coastline change is superior to the Philippine islands.On island scale,the coastline of Java,Batam,Indonesia,Singapore and so on,islands with large population,high economic level,and low terrain,change more prominent in coastline.On local scale,island changes of the river deltas,gulf and the straits are more significant as well.In terms of time series,the intensity and range of coastline changes from 2000 to 2015 were greater than those from 1990 to2000 as a whole.(4)The coastline changes have spatial correlation property.In natural state,the coastline erosion and expansion are always accompanied,which is considered in dynamic equilibrium state within a certain space and time scale.It is relate to the sediment migration mode,coastal ecosystem self-feedback and regulation mechanism in the natural state.(5)The main factors affecting the coastline changes of the island include human and natural factors.The former are such as population growth,urbanization,aquaculture,deforestation,commercial sand mining,construction of port,dam,airport,and military base,etc.,and natural factors are such as coastal material composition and topography,self-regulation of coastal ecosystems(mangroves,salt marshes,and coral reefs),wave systems,sea level rise,storm surges,tsunamis and other extreme events etc.(6)In summary,there are two main ways to influence coastline changes.One is that change the spatial location and use type of the coastline directly,such as reclamation and seawater intrusion,and another is that change the coastline position though influence the supply and transportation of sediments.Natural environmental factors are still the main factors affecting the islands and coastlines along the Maritime Silk Road,and the impact of human activities is relatively severe but the influencing space is relatively limited.In addition,sea level rise has not caused extensive erosion of the island coastline in this study area,and is still only one of the factors aggravating coastline erosion,rather than the dominant factor.