Affiliation:
1. School of Earth Sciences, Zhejiang University, Hangzhou 310058, China
2. Hainan Institute, Zhejiang University, Sanya 572000, China
3. Institute for Ocean Engineering, Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
Abstract
As one of the most important ecosystems, the water body is losing water during the rapid development of the city. To understand the impacts on water body change during the rapid urbanization period, this study combines data from the OpenStreetMap platform with Landsat 5/Thematic Mapper images to effectively and accurately identify small urban water bodies. The findings indicate that the trained U-net convolutional neural network (U-Net) water body extraction model and loss function combining Focal Loss and Dice Loss adopted in this study demonstrate high precision in identifying water bodies within the main urban area of Hangzhou, with an accuracy rate of 94.3%. Trends of decrease in water areas with a continuous increase in landscape fragmentation, particularly for the plain river network, were observed from 1985 to 2010, indicating a weaker connection between water bodies resulting from rapid urbanization. Large patches of water bodies, such as natural lakes and big rivers, located at divisions at the edge of the city are susceptible to disappearing during the rapid outward expansion. However, due to the limitations and strict control of development, water bodies, referring to as wetland, slender canals, and plain river networks, in the traditional center division of the city, are preserved well. Combined with the random forest classification method and the U-Net water body extraction model, land use changes from 1985 to 2010 are calculated. Reclamation along the Qiantang River accounts for the largest conversion area between water bodies and cultivated land, constituting more than 90% of the total land use change area, followed by the conversion of water bodies into construction land, particularly in the northeast of Xixi Wetland. Notably, the conversion of various land use types within Xixi Wetland into construction land plays a significant role in the rise of the carbon footprint.
Funder
Hainan Province Science and Technology Special Fund of the Hain Provincial Department of Science and Technology
National Natural Science Foundation of China
Zhejiang Provincial Natural Science Foundation of China
Reference47 articles.
1. Urban surface water body detection with suppressed built-up noise based on water indices from Sentinel-2 MSI imagery;Yang;Remote Sens. Environ.,2018
2. Analysis of scale effect and change characteristics of ecological landscape pattern in urban waters;Wang;Arab. J. Geosci.,2021
3. Morphological characteristics of urban water bodies: Mechanisms of change and implications for ecosystem function;Steele;Ecol. Appl.,2014
4. Chen, L., Zhou, B., Man, W., and Liu, M. (2021). Landsat-Based Monitoring of the Heat Effects of Urbanization Directions and Types in Hangzhou City from 2000 to 2020. Remote Sens., 13.
5. Field measurements of the spectral response of natural waters;Bartolucci;Photogramm. Eng. Remote Sens.,1977