Numerical Simulation and Risk Evaluation of Urban Flooding based on High-resolution Remote Sensing

Fig. 2. Model of drainage system of the study area

Fig. 3. Framework of model simulation

Fig. 4. Framework of terrain extraction

Fig. 5. Framework of urban waterlogging numerical simulation

Fig. 6. 3D DEM （with buildings and topography） of the study area in 2017 and 2021

Fig. 7. Extraction results of the underlying surface information of the study area in 2017 and 2021

Fig. 8. Simulation results of waterlogging in 2017

Fig. 9. Simulation results of waterlogging in 2021

Fig. 10. Water flow movement at different unit scales （Black arrows in the figure represent the direction of runoff and the length represents velocity）

Fig. 11. Satellite image and live view of Point 1 located at Keyuan MTR station

Fig. 12. Satellite image and live view of Point 2 located at parking lot of the industry-academy research base

Fig. 13. Changes in water depth at Points 1 and 2 under the 1-in-100-year rainfall scenario

Fig. 14. Risk level of waterlogging in 2017 and 2021

Table 1. Table 1Urban waterlogging risk assessment criteria

Table 1. Table 1Urban waterlogging risk assessment criteria

风险等级	影响因素
	水深h(m)		流速v(m/s)		影响面积A(m²)		人口密度ρ(人/km²)
	阈值	评价值	阈值	评价值	阈值	评价值	阈值	评价值
低	<0.15	30	<0.4	30	<100	30	<1 000	30
中	0.15~0.6	50	0.4~0.8	50	100~1 000	50	1 000~2 000	50
高	0.6~1.2	70	0.8~1.5	70	1 000~10 000	70	2 000~5 000	70
极高	>1.2	90	>1.5	90	>10 000	90	>10 000	90

Table 2. Table 2Confusion matrix for underlayment accuracy verification

Table 2. Table 2Confusion matrix for underlayment accuracy verification

类别	小区内部硬化地面	建筑物	市政道路	园林绿地	水域	裸地	总和	用户精度/%
总体精度：82.29%
小区内部硬化地面	34	8	1	3	0	1	47	65.38
建筑物	9	63	6	0	2	1	81	77.78
市政道路	8	7	41	5	2	1	64	83.67
园林绿地	0	3	1	120	2	2	128	92.31
水域	0	0	0	0	21	0	21	77.78
裸地	1	0	0	2	0	23	26	82.14
总和	52	81	49	130	27	28	367
生产者精度/%	72.34	77.78	64.06	93.75	100.00	88.46

Table 3. Table 3Depth and area of waterlogging in different years and recurrence periods

Table 3. Table 3Depth and area of waterlogging in different years and recurrence periods

	2017年积水面积/km²				2021年积水面积/km²
积水深度	<0.15 m	0.15~0.6 m	0.6~1.2 m	>1.2 m	<0.15 m	0.15~0.6 m	0.6~1.2 m	>1.2 m
20年一遇	0.094 6	0.217 3	0.133 1	0.040 6	0.067 6	0.156 6	0.109 9	0.042 0
50年一遇	0.092 4	0.222 4	0.160 4	0.052 9	0.070 0	0.161 9	0.127 9	0.057 5
100年一遇	0.091 6	0.221 2	0.177 5	0.063 9	0.070 4	0.164 6	0.138 2	0.069 8

Table 4. Table 4Accuracy of numerical simulation models for waterlogging

Table 4. Table 4Accuracy of numerical simulation models for waterlogging

积水测站编号	0000000115	0000000128
积水测站位置	创盛路新能源产业园	西丽塘朗工业区B区
积水测站实测积水深度	0.17 m	1.35 m
城市内涝积水数值模拟结果	0.20 m	1.55 m
精度	82.35%	85.19%

Table 5. Table 5Accuracy of waterlogging depth for different resolution DEMs
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Table 5. Table 5Accuracy of waterlogging depth for different resolution DEMs
DEM网格大小
2.5 m 5.0 m 10.0 m 20.0 m
积水深度相对精度/% 1 h 100.00 94.69 76.12 41.91
2 h 100.00 97.06 94.58 68.62
24 h 100.00 97.12 96.55 75.86

Table 6. Table 6Comparison of underlying surface categories and water depth
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Table 6. Table 6Comparison of underlying surface categories and water depth
年份点号
不透水面占比
/%
园林绿地和裸地占比
/%
最大积水深度
/m
2017年 1 46.10 53.90 0.58
2 82.43 17.57 0.59
2021年 1 78.01 21.99 1.14
2 68.00 32.00 0.13

Table 7. Table 7Changes statistics for underlying information and waterlogged area of 2017<bold>~</bold>2021

Table 7. Table 7Changes statistics for underlying information and waterlogged area of 2017<bold>~</bold>2021

		2017年		2021年		面积变化/km²
		面积/km²	占比/%	面积/km²	占比/%	面积变化/km²
研究区下垫面	小区内部硬化地面	1.160 7	35.97	1.220 7	37.70	+0.060 0
	建筑物	0.523 9	16.24	0.556 7	17.20	+0.032 8
	市政道路	0.449 2	13.92	0.449 8	13.89	+0.000 6
	园林绿地	0.925 2	28.67	0.846 6	26.15	-0.078 6
	水域	0.081 0	2.51	0.081 9	2.53	+0.000 9
	裸地	0.086 8	2.69	0.081 9	2.53	-0.005 0
积水面积	20年一遇降雨	0.485 6	14.98	0.376 1	11.60	-0.109 5
	50年一遇降雨	0.528 1	16.29	0.417 3	12.87	-0.110 8
	100年一遇降雨	0.554 2	17.09	0.443 0	13.66	-0.111 2

Table 8. Table 8Results of risk assessment of 2017<bold>~</bold>2021 of the study area