Monitoring And Evaluation Of Island Ecological Environment Based On Remote Sensing:a Case Study Of The Zhoushan Islands

Islands as sea treasures, not only rich in natural resources, but also function as natural barriers to coastal cities. Affected by sea-level rise and high intensity of human development activities, island ecological environment health is facing serious challenges. To provide background information for future study on coastal protection and management, long term remote sensing images and geographic information system technologies were used to monitor and evaluate the situation of ecological environment in the Zhoushan Islands. In this paper, the research works as below were done:(1) Monitoring and analysis of impervious surface dynamics in the Zhoushan Islands. Increasing impervious surfaces in the Zhoushan Islands due to new development and increased population have an ecological impact on the runoff and water quality. Based on time-series classification and the complement of vegetation fraction in urban regions, Landsat Thematic Mapper (TM) and other high-resolution satellite images were applied to monitor the dynamics of impervious surface area (ISA) in the Zhoushan Islands during1986-2011. Landsat-derived ISA results were validated by the high-resolution Worldview-2and aerial photographs. The validation shows that mean relative errors of these ISA maps are less than15%. The results reveal that the ISA in the Zhoushan Islands increased from19.2km2in1986to86.5km2in2011, and the period from2006to2011had the fastest expansion rate of5.59km2per year. The major land conversions to high densities of ISA were from the tidal zone and arable lands. The expansions of ISA were unevenly distributed and most of them were located along the periphery of these islands. Time-series maps revealed that ISA expansions happened continuously over the last25years. Our analysis indicated that the policy and the topography were the dominant factors controlling the spatial patterns of ISA and its expansions in the Zhoushan Islands. With continuous urbanization process, the rapid ISA expansions may not be stopped in the near future.(2) Evaluation of coastline changes under human intervention along the Zhoushan coast. Continued sea-level rise and coastal development have led to considerable concerns on coastline changes along inhabited islands. Analysis of long-term coastline changes of islands is however limited due to unavailable data and the cost of field work. In this study, high-resolution images taken from1970-2011at an interval of about10years and topographic maps were collected to determine coastline changes and their drivers in the Zhoushan Islands, China. Results show that nearly all inhabited islands appeared to have noteworthy seaward expansion during the past four decades. Coastline change rates varied among islands, and the annual change rate of Zhoushan Island (the main island) reached12.83±0.17m/yr during the same period. Since2003, the study area has been dominated by artificial coast. The proportion of harbor/port and urban/industrial coast has significantly increased, while rocky coasts and shelter-farm coasts have shrunk greatly. Preliminary analysis of drivers for these coastline changes across the Zhoushan Islands highlights the roles of human policies during different periods as well as location, which were the dominant factors controlling the great spatial and temporal complexity of coastline changes of the major islands. Sediment supply from the Yangtze River decreased after the completion of the Three Gorges Dam in2003; however, the Zhoushan coast rapidly accreted seaward during the last decade and the artificial siltation, coastal engineering, and harbor dredging materials could be responsible for the observed coastline changes. Pressured by rapid development of the port industry, the Zhoushan coast may face unprecedented challenges in coastal use in the near future. This research provides the basic background information for future studies on coastal protection and management.(3) Resilience assessment of the island in facing typhoon disasters. The sustainable development in the ocean and coastal areas has been an issue for island regions. Most of the vulnerability researches have been conducted based on pressures, damages that involved in the regions, while the researches of the ability to withstand the recovery process in facing marine disasters (i.e., typhoons, storm surges) are less reported. Therefore, in order to evaluate the vulnerability of the Zhoushan Islands in facing typhoon disasters, this paper aims to create an island resilience index compositing natural and socio-economic variables. The results revealed that the total resilience of the Zhoushan Islands showed down trend over the past30years, and the natural resilience index has a slight decrease while the socio-economic resilience index has a rapid decrease. Comparing the changes of socio-economic resilience during periods of1990-2000and2000-2011, it shows that the period2000-2011reduced by less than the period1990-2000. This indicates that under the influences of human activities, the Zhoushan Islands showed increased vulnerability, but the positive responses in terms of freshwater, transportation and disaster prevention facilities reduce the decrease of resilience during the past decade. Spatially, Zhoushan Island and Jintang Island are in lower vulnerability, and islands Fuchi, Xixiezhi and Xiaogan are in higher vulnerability, and other surrounding islands are in moderate vulnerability. Totally, the island resilience is mainly affected by indicators of island area, vegetation, population density and land use, and percentage of impervious surface areas as well as transportation (i.e. harbor/port, trans-oceanic bridges).