Author Contributions
Conceptualization, X.Z., J.L. and R.L.; Methodology, M.W.; Software, M.W.; Validation, R.B.; Formal analysis, M.W., X.Z and L.B.; Investigation, X.Z.; Resources, X.Z. and C.S.; Data curation, M.W. and R.B.; Writing—original draft, M.W.; Writing—review & editing, R.B. and X.Z.; Visualization, L.B.; Supervision, X.Z.; Project administration, X.Z.; Funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.
Figure 1.
(a) Location of Hangzhou City (indicated by a red dot ●) on a digital elevation map including Anhui, Jiangsu, and Zhejiang Provinces and Shanghai City within the Yangtze River Delta; the map comes from the US National Aeronautics and Space Administration’s Shuttle Radar Topography Mission and has a 90 m resolution. (b) For administrative divisions of Hangzhou in 2021, data is sourced from the National Geographic Information Resources Directory Service.
Figure 1.
(a) Location of Hangzhou City (indicated by a red dot ●) on a digital elevation map including Anhui, Jiangsu, and Zhejiang Provinces and Shanghai City within the Yangtze River Delta; the map comes from the US National Aeronautics and Space Administration’s Shuttle Radar Topography Mission and has a 90 m resolution. (b) For administrative divisions of Hangzhou in 2021, data is sourced from the National Geographic Information Resources Directory Service.
Figure 2.
The technical roadmap of this study. Note: MNDWI, modified normalized difference water index; AWEI, automated water body extraction index (AWEI); SVM, support vector machine; and OSM, OpenStreetMap software.
Figure 2.
The technical roadmap of this study. Note: MNDWI, modified normalized difference water index; AWEI, automated water body extraction index (AWEI); SVM, support vector machine; and OSM, OpenStreetMap software.
Figure 3.
Labelling data of the water body for Hangzhou City that aligns with the satellite images: (a) original Landsat 5/Thematic Mapper image of Hangzhou City in 2010; (b) labeling data of the water body processed by ArcGIS.
Figure 3.
Labelling data of the water body for Hangzhou City that aligns with the satellite images: (a) original Landsat 5/Thematic Mapper image of Hangzhou City in 2010; (b) labeling data of the water body processed by ArcGIS.
Figure 4.
Training process of water body extraction algorithm based on the U-Net model. Note: OSM, OpenStreetMap platform.
Figure 4.
Training process of water body extraction algorithm based on the U-Net model. Note: OSM, OpenStreetMap platform.
Figure 5.
Comparison of water body extraction results by different methods: (a) the original Land-sat5/Thematic Mapper image acquired in 2010; (b) modified normalized difference water index; (c) automated water body extraction index; (d) SVM; and (e) U-Net.
Figure 5.
Comparison of water body extraction results by different methods: (a) the original Land-sat5/Thematic Mapper image acquired in 2010; (b) modified normalized difference water index; (c) automated water body extraction index; (d) SVM; and (e) U-Net.
Figure 6.
Water body extraction results of the U-Net model every 2 years from 1986 to 2010 are shown in (a–m), respectively.
Figure 6.
Water body extraction results of the U-Net model every 2 years from 1986 to 2010 are shown in (a–m), respectively.
Figure 7.
Biennial changes of water area from 1986 to 2010 in the main urban area of Hangzhou, Zhejiang, China.
Figure 7.
Biennial changes of water area from 1986 to 2010 in the main urban area of Hangzhou, Zhejiang, China.
Figure 8.
Water body extraction from Xixi Wetland every 2 years from 1990 to 2000 is shown in (a–f), respectively.
Figure 8.
Water body extraction from Xixi Wetland every 2 years from 1990 to 2000 is shown in (a–f), respectively.
Figure 9.
Reduction of water area of Xixi Wetland every 2 years from 1990 to 2000.
Figure 9.
Reduction of water area of Xixi Wetland every 2 years from 1990 to 2000.
Figure 10.
Tailored Landsat5/Thematic Mapper image where the Qiantang River meanders through Zhejiang Province. The red square represents part of the main urban area of Hangzhou, where the Qiantang River flows. The blue shading represents the section of the Qiantang River with dramatic change.
Figure 10.
Tailored Landsat5/Thematic Mapper image where the Qiantang River meanders through Zhejiang Province. The red square represents part of the main urban area of Hangzhou, where the Qiantang River flows. The blue shading represents the section of the Qiantang River with dramatic change.
Figure 11.
Significant variation in the water area in the eastern side of the Qiantang River in the main urban area of Hangzhou in (a) 1986–1988, (b) 1992–1996, (c) 2004–2008, and (d) Graph of the biennial changes in the water area of the Qiantang River in the main urban area of Hangzhou City from 1986 to 2010.
Figure 11.
Significant variation in the water area in the eastern side of the Qiantang River in the main urban area of Hangzhou in (a) 1986–1988, (b) 1992–1996, (c) 2004–2008, and (d) Graph of the biennial changes in the water area of the Qiantang River in the main urban area of Hangzhou City from 1986 to 2010.
Figure 12.
Graph of the biennial changes in the number of water body patches and landscape fragmentation from 1986 to 2010.
Figure 12.
Graph of the biennial changes in the number of water body patches and landscape fragmentation from 1986 to 2010.
Figure 13.
The variation of both the water area and fragmentation with different sizes.
Figure 13.
The variation of both the water area and fragmentation with different sizes.
Figure 14.
The variation of both the water area and fragmentation in different divisions.
Figure 14.
The variation of both the water area and fragmentation in different divisions.
Figure 15.
Land use classification results every 5 years from 1985 to 2020 are shown in (a–f), respectively.
Figure 15.
Land use classification results every 5 years from 1985 to 2020 are shown in (a–f), respectively.
Figure 16.
Biennial changes in (a) landscape fragmentation and (b) carbon footprint from 1985 to 2010.
Figure 16.
Biennial changes in (a) landscape fragmentation and (b) carbon footprint from 1985 to 2010.
Table 2.
Criteria for water body and non-water land classification results.
Table 2.
Criteria for water body and non-water land classification results.
| True Value | Water | Non-Water |
Predicted Value | |
Water body | True positive | False positive |
Non-water body | False negative | True negative |
Table 3.
Water body extraction accuracy evaluation of different methods.
Table 3.
Water body extraction accuracy evaluation of different methods.
Method | Accuracy | Precision | Recall | F1 Score | mIoU | Training Times |
---|
MNDWI | 0.862 | 0.853 | 0.849 | 0.857 | 0.842 | 2 min |
AWEI | 0.901 | 0.893 | 0.884 | 0.871 | 0.870 | 5 min |
SVM | 0.889 | 0.892 | 0.878 | 0.867 | 0.870 | 30 min |
U-Net | 0.943 | 0.952 | 0.919 | 0.937 | 0.891 | 48 h |
Table 4.
Results of the landscape fragmentation index from 1986 to 2010.
Table 4.
Results of the landscape fragmentation index from 1986 to 2010.
Year | NP | CA | C |
---|
1986 | 1301 | 317.29 | 4.10 |
1988 | 1332 | 283.44 | 4.70 |
1990 | 1297 | 283.12 | 4.58 |
1992 | 1288 | 280.36 | 4.60 |
1994 | 1296 | 267.80 | 4.84 |
1996 | 1310 | 256.30 | 5.11 |
1998 | 1322 | 254.16 | 5.20 |
2000 | 1457 | 256.60 | 5.69 |
2002 | 1456 | 256.31 | 5.68 |
2004 | 1442 | 252.54 | 5.71 |
2006 | 1369 | 234.38 | 5.84 |
2008 | 1287 | 225.37 | 5.71 |
2010 | 1256 | 221.91 | 5.66 |
Table 5.
Carbon footprint coefficients of various land use types.
Table 5.
Carbon footprint coefficients of various land use types.
Land Use Type | Cultivated Land [43] | Woodland [44] | Grassland [44] | Water Area [45] | Unused Land [45] | Construction Land [46] |
Carbon footprint coefficient (t·hm−2) | 0.497 | −0.644 | −0.021 | −0.218 | −0.005 | 65.300 |
Table 6.
Net conversion areas (km2) of water bodies to five land use types.
Table 6.
Net conversion areas (km2) of water bodies to five land use types.
Year | Land Use Types |
---|
Cultivated Land | Woodland | Grassland | Construction Land | Unused Land |
---|
1985–1990 | 3756 | −12 | −1 | 18 | 0.00 |
1990–1995 | 1134 | −15 | 0.00 | 134 | 0.00 |
1995–2000 | 971 | −24 | 5 | 203 | 0.00 |
2000–2005 | 1768 | 56 | 11 | 334 | 0.18 |
2005–2010 | 1160 | 2 | 1 | 39 | −2 |
Table 7.
Changes in carbon footprint from water bodies compared to other land use types.
Table 7.
Changes in carbon footprint from water bodies compared to other land use types.
Year | 1985–1990 | 1990–1995 | 1995–2000 | 2000−2005 | 2005−2010 |
Carbon footprint/t | 3068 | 9324 | 13,762 | 23,521 | 3096 |