Long-term Continuous Monitoring Of Island Urbanization And Its Ecological Consequences

Islands are undergoing rapid industrialization and urbanization with ever-increasing coastal developments.Due to the limited sizes and resources,and isolation from mainland,islands are more sensitive to anthropogenic disturbance compared with continental areas.Therefore,it is of great significance to monitor the island urbanization pattern and its ecological consequences for supporting future policy making for sustainable development.Previous studies were generally conducted at relatively coarse temporal intervals(e.g.5 or 10 years),which hardly captured detailed island environmental dynamics.This study coupled pattern and process as an intergrated framework,and developed efficient,accurate and long-term continuous monitoring methods in the Google Earth Engine platform to map the annual coastal dynamics and urban sprawl pattern in the Zhoushan Archipelago during 1986-2017 using all the available Landsat images(?2000 scenes).Furthermore,this study quantified the changes of net primary productivity(NPP)and habitat quality as the indicators of the ecological consequences of urbanization.(1)Developed a new method to monitoring the coastal dynamics which could accurately capture the conversion types and change time of the coastal cover types.The method used the temporal segmentatation and tidal height analysis to detecte the annual spatial pattern of land,tidal flat,and water during 1986?2017.Results indicate that the proposed method could well identify turning years with an overall accuracy of 91% and map coastal cover types with overall accuracies within 89?94% in 1986 and 87?92% in 2017.Significant coastline expansions and declines in tidal flats were found in the study area.The areas of tidal flats decreased by 6 km2 during 1986-2017,while the land area increased by 153 km2.The land reclamation was accelerated after 2003,and the land reclamation area during 2003-2017 was about 10 times that during1986-2003.(2)Proposed an efficient framework by intergrating the random forest classifier and change detection method to map the annual island urban patterns.Results showed that the proposed method could well identify urbanized years with an overall accuracy of 86% and map land use/land covers with overall accuracies of 94% in 1986,94% in 2001,and 93% in 2017.The urban area expanded from 97 km2 in 1986 to 456 km2 in 2017,increasing nearly 4 times with the average annual growth rate of 5%.The newly urbanized areas were converted from agricultural lands(161.3 km2),waters(141.1 km2),forests(42.0 km2)and tidal flats(13.7 km2).The urbanization progress had two periods according to its growth rates:(1)slow growth period(1986-2004): the annual urban increment was below 10 km2 with a total growth of 63 km2,and(2)rapid growth period(2004-2017): the annual urban increment was between 10 and 35 km2 with a total growth of 295 km2.(3)The Carnegie-Ames-Stanford Approach(CASA)model was adopted to estimate the annual NPP and the Integrated Valuation of Ecosystem Services and Tradeoffs(In VEST)model was employed to estimate and map the annual habitat quality.Results showed that the annual NPP decreased from 106 Gg C in 1986 to 50 Gg in 2017 in the newly urbanized areas,specifically,the 91 % of the decrease was caused by urban sprawl while the remaining 9 % was caused by climate change.The estimated habitat quality showed that the area with high habitat quality decreased from 926 km2 in 1986 to 757 km2 in 2017,with a decrease of 18%;and the area of moderate habitat quality decreased from 462 km2 to 304 km2,with a decrease of 34%.The annual NPP and habitat quality dynamics showed similar change paces to urban sprawl which was first slow and then accelerated.(4)Different island development types showed three different change characteristics:(1)siginificant change types,including the comprehensive development islands,harbor and logistics islands,coastal industry islands and coastal tourism islands.Specifically,their reclamation area accounted for 54%,20%,14% and 8% of the total amount in the study area respectively;their new urban area accounted for 64%,15%,11% and 8% respectively;their decrease of NPP accounted for 63%,18%,8% and 9% respectively;their decrease of high habitat quality area accounted for 56%,21%,10% and 9%,respectively;and their decrease of moderate habitat quality area accounted for 71%,9%,4% and 13%,respectively.(2)slight change types,including marine science and education islands,and scientific fishery islands,where the coastal dynamics,urban growth,and ecosystem services changes only accounted for about 2% of total change amount in the study area.(3)stable types,including clean energy islands and ecological conversation islands,where the ecological environments were well protected.This study provides an empirical analysis of the long-term continuous island urbanization and its ecological consequences under the background of rapid urbanization,which are of great uses for the urban planning,sustainable development and ecological protection of the islands.In addition,the proposed framework based on the Google Earth Engine platform and Landsat time series images is transferable to other coastal areas to support the monitoring of the global ecological environment.