Increased coverage of impervious surfaces is an important measure of urban sprawl, and understanding spatiotemporal dynamics of impervious surfaces is vital for regional and local development. Combining vegetation-impervious-surfaces oil model and linear spectral unmixing model, this paper used the Landsat TM and OLI remote sensing data from 2009 to 2019 to study the temporal and spatial variation characteristics of the impervious surfaces of Zhengzhou, and discussed the main driving factors leading to urban expansion. We found that impervious surface growth in the main urban area of Zhengzhou City was obvious, and the area of impervious surfaces increased from 337.52 km2 in 2009 to 464.93 km2 in 2019, with an average expansion speed of 12.69 km2 /year. The impervious surfaces pattern of the research area changed significantly, and the expansion of impervious surface showed a flaky development in all directions. From 2009 to 2014, Zhengzhou’s expansion was mainly concentrated in Hi-Tech Industrial Development Zone, Zhongyuan District, as well as Economic and Technological Development Zone. Most of the expansion between 2014 and 2019 was concentrated in Zhengdong New District and Huiji District. Physical geography, urban population, GDP and national policies were the main drivers affecting the expansion of impervious surfaces.
Zhengzhou City suffered the strongest rainstorm in history in July 2021, floods and other secondary disasters have greatly endangered the property and safety of local residents in Henan Province, China. In this paper, the flood risk of Henan Province was analyzed from the three perspectives of hazard, exposure and vulnerability, and seven factors of rainfall, elevation, slope, distribution density of river network, population, GDP and arable land occupation ratio were selected to create a flood disaster risk evaluation index system. Remotely sensed data and GIS were used to analyze and map the influencing factors, and then the comprehensive risk results of flood disasters in Henan Province were obtained based on analytic hierarchy process (AHP) method. Results show that the higher-risk area and high-risk area mainly locate in cities of Xinyang, Luohe, Zhumadian, Zhoukou and Xuchang, as well as the north of Zhengzhou, accounting for 43% of the total area of Henan Province. High risk area is mainly caused by high hazard of the flat terrain and abundant rainfall. The lower-risk area is mainly distributed in Sanmenxia, Jiyuan and Anyang, and the western part of Luoyang, that locate in high-elevation areas, and the vulnerability index of GDP is low in these areas. The rest of the areas are medium-risk areas. This research provides the background information for disaster prevention and mitigation management in Henan Province.
The largest inhabited island, Zhoushan Island, is the center of economy, culture, shipping, and fishing in the Zhoushan
Archipelago New Area. Its coastal wetland and tidal flats offer significant ecological services including floodwater
storage, wildlife habitat, and buffers against tidal surges. Yet, large-scale land reclamation and new land development
may dramatically change ecosystem services. In this research, we assess changes in ecosystem service values in
Zhoushan Island during 1990-2000-2011. Three LANDSAT TM and/or ETM data sets were used to determine the
spatial pattern of land use, and previously published value coefficients were used to calculate the ecosystem service
values delivered by each land category. The results show that total value of ecosystem services in Zhoushan Island
declined by 11% from 2920.07 billion Yuan to 2609.77 billion Yuan per year between 1990 and 2011. This decrease is
largely attributable to the 51% loss of tidal flats. The combined ecosystem service values of woodland, paddy land and
tidal flats were over 90% of the total values. The result indicates that future land-use policy should pay attention to the
conservation of these ecosystems over uncontrolled reclamation and coastal industrial development, and that further
coastal reclamation should be on rigorous environmental impact analyses.
Increased impervious surfaces pose significant threats to the hydrologic cycle of the Xiangjiang River basin as a consequence of urbanization. Quantifying the percentage of imperviousness within the Xiangjiang River basin is important to pollution control and watershed management. Per-pixel and sub-pixel methods have been widely used for analyzing impervious surface changes, but these methods are considered as complicated, computationally intensive, and sometimes subjective, especially when applied to a large geographic area. In this paper, normalized difference built-up index (NDBI), normalized difference impervious surface index (NDISI), normalized difference vegetation index (NDVI) and enhanced built-up and bareness index (EBBI) were respectively used to estimate impervious surfaces in Chang-ZhuTan region (CZT) of the Xiangjiang River basin, and a comparative analyses was conducted. Then the optimum spectral index was chosen to map the percentage of impervious surfaces for the study area. The results show that the spectral index of NDBI has the optimum estimation of large-scale impervious surfaces, and the percentage of imperviousness in CZT was 13.87%. The water quality in CZT was characterized as “protected”, indicating that water quality protection in the plain areas of CZT is imperative.
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