## 3 Experimental Results and Analysis
### Analysis of Spatial and Temporal Changes in Impervious Surfaces  
Figure 3 shows the distribution of impervious areas in Xuzhou City in 2013, 2018, and 2022 (2013-2022 Xuzhou City Impervious Surface Extraction Results in Supplementary Materials), as well as the change in the impervious surface distribution. From Figure 3d, it can be seen that the distribution of impervious areas in the center of Xuzhou City is relatively stable. In order to further analyze the change rule of impervious areas in Xuzhou city from 2013 to 2022, the impervious area of Xuzhou city in each year was calculated and linearly analyzed; as shown in Figure 4, the impervious area of Xuzhou city increased by 637.17 km\({}^{2}\) from 2013 to 2022.  
Figure 2: Overview of the study area. (Standard map with review number GS (2016) 2923 downloaded from the website of the Standard Map Service of the Ministry of Natural Resources).  
The change in impervious surfaces was analyzed based on the growth trend of impervious surfaces by dividing it into two phases, 2013-2018 and 2018-2022. During the period of 2013-2018, the growth of impervious surface areas was higher in 2013-2016, with an increase of 101.73 km\({}^{2}\) and 127.86 km\({}^{2}\), respectively; in 2016-2018, the growth rate became slower, increasing by 10.15 km\({}^{2}\) and 9.17 km\({}^{2}\), respectively. In the phase 2018-2022, there was an increase of 86.30 km\({}^{2}\), 102.32 km\({}^{2}\), and 78.79 km\({}^{2}\) in the years 2018-2021, while there was only an increase of 11.69 km\({}^{2}\) in the period 2021-2022. Both phases of impervious surface area change were characterized by a rapid increase in impervious surface followed by stabilization, with a period of plateauing after a period of substantial growth in impervious surfaces. Analyzing the distribution of impervious surfaces in the counties and cities of Xuzhou City from 2013 to mid-2022, it can be found that the distribution of impervious surfaces in the Quanshan District, the Gulou District, and the Yunlong District is the most intensive. More than 30% of the area has impervious surfaces, and Feng County  
Figure 3: The distribution of impervious surfaces in Xuzhou City from 2013 to 2022. (**a–c**) show the impervious area extraction results for Xuzhou City in 2013, 2018 and 2022, respectively. (**d**) Changes in the distribution of impervious surface in some areas of Xuzhou City in 2013, 2018 and 2022.  
has the smallest percentage of impervious surfaces, with only about 7% of the area having impervious surfaces. Tongshan District had the largest increase in impervious surfaces, with an increase of 112.74 km\({}^{2}\), and Feng County had the fastest growth rate of impervious surfaces of 94.15 percent, with an increase of 98.99 km\({}^{2}\).  
The method accuracy and Kappa coefficient of each type of feature calculated as shown in the confusion matrix can determine whether the classification method used is usable or not. The Kappa coefficient is a metric used for consistency testing, a measure of consistency in statistics with values in the range of [\(-\)1, 1], which provides a good measure of the consistency between predicted and actual classification results. In the original image of the study area, 150 sample points were selected, among which 50 sample points were selected for water bodies, vegetation, bare soil, and impervious surfaces, ensuring that the selected sample points were randomly taken and uniformly distributed. The user accuracies were greater than 90% in the years 2013-2022, which demonstrated the reliability of the classification method, and the user accuracies and Kappa of impervious surfaces in the years 2013-2022 are shown in Table 1.