Co-occurrence of pluvial and fluvial floods exacerbates inundation and economic losses: evidence from a scenario-based analysis in Longyan, China

Figures & data

Figure 1. Map of Longyan city center, including its location, rivers, buildings and roads.

Figure 2. Framework for compound flood simulation and impact assessment.

Table 1. Data sources for compound flood simulation and impact assessment.

Data category	Contents	Description	Source
Unmanned Aerial Vehicle (UAV) remote sensing	Digital orthophoto map (DOM)	Used to extract the elevation for sampled channel section of river.	Drone aerial photography
	Digital surface model (DSM)	Used for two-dimensional simulation of overland flow by the MIKE 21 model
Meteorological data	Rainfall data	Used as model input and for model calibration and validation	Longyan Meteorological Bureau
Hydrological data	Flow data	Used as model input and for model calibration and validation	Longyan Hydrological Bureau
Geospatial data	1:2000 digital map	Contains built-up land, roads, green space, water, river network and other layers, which are used to generate land use data, as an input to the hydrodynamic model.	Longyan Natural Resources and Planning Bureau
	1:1000 elevation point data	Used to generate the digital elevation model (DEM) of the study area	Longyan Natural Resources and Planning Bureau
	Underground pipe network data	Used as the input to the pluvial flood model	Longyan Natural Resources and Planning Bureau
	Spatial distribution map of major buildings	Location, area and height of different buildings including residential, office, commercial, industrial, etc.; used for flood loss assessment	Longyan Natural Resources and Planning Bureau
	Spatial distribution map of major roads	Location, length and width of major urban roads; used for flood loss assessment	Longyan Natural Resources and Planning Bureau
	Spatial distribution map of major electrical facilities	Location of major electrical facilities; used for flood loss assessment	Longyan Natural Resources and Planning Bureau
Statistical data	Construction cost of various building types	Per floor area construction cost of residential, office, commercial and industrial buildings. from Bureau of Construction Administration: used for flood loss assessment	Longyan Construction Bureau
	Indoor property in various building types	Market values of indoor durable goods such as furniture and household appliances; market values of major equipment in factories, etc.; used for flood loss assessment	Longyan Statistics Bureau; Longyan Civil Affairs Bureau
	Construction cost of different types of roads	Construction cost per unit length of different types of roads; used for flood loss assessment	Longyan Construction Bureau
	Construction cost of different types of electrical facilities	Construction cost of electricity substations and transmission lines, etc.; used for flood loss assessment	State Grid

Table 2. Maximum hourly precipitation for a short-term rainfall and a long-term rainfall.

Rainfall type	Return period	Precipitation (mm)
Short-term rainfall (Local 2-hour rainfall)	1-year	24.8
	2-year	40.5
	10-year	55.8
	50-year	67.4
Long-term rainfall (Upstream 24-hour rainfall)	20-year	49.7
	50-year	55
	100-year	60
	200-year	64.1

Figure 3. Design rainstorm distribution process for different return periods.

Table 3. Validation of the SWAT model.

Stations	R^2	NS	RMSE(m³/s)
Longmen	0.85	0.80	59.42
Chenpo	0.82	0.77	83.56
Xiaoxi	0.83	0.78	75.90

Table 4. Validation of the MIKE 11 HD model.

Date	Location	Simulated flood peak (m)	Observed flood peak (m)	Errors(m)
2005/8/14	Longmen site	325.24	325.14	0.10
2005/8/14	Xiaoxi site	325.37	325.41	0.04
2019/6/12	Chenpo site	322.19	322.3	0.11

Table 5. Performance of the pluvial flood model.

Inundation sites	Simulated inundation depth (m)	Observed inundation depth (m)	Errors (%)
1	0.24	0.21	14.3
2	0.70	0.66	6.1
3	0.27	0.23	17.4
4	0.15	0.17	11.8

Table 6. Vulnerability curves for building, road and Electricity facility.

Item	Vulnerability curve
Building structure	$V(h)=0.0056h^3-0.032h^2+0.169h+0.041$
Building content	$V(h)=-0.0265h^3-0.0488h^2+0.7423h-0.1149$
Road	$V(h)=0.044194h$
Electricity facility	$V(h)=0.04068h-0.873$

Figure 4. Maximum inundation extents and depths in the cases of (a) 1-year, (b) 2-year, (c) 10-year, and (d) 50-year return period pluvial floods.

Figure 5. Maximum inundation extents and depths in the cases of (a) 20-year, (b) 50-year, (c) 100-year, and (d) 200-year return period fluvial floods.

Figure 6. Maximum inundation extents and depths of compound floods: (a) combined 10-year pluvial and 50-year fluvial floods; (b) combined 50-year pluvial and 200-year fluvial floods.

Figure 7. Direct economic losses of pluvial floods on urban physical systems: (a) total economic losses, (b) building structures, (c) building contents, (d) roads, and (e) electrical facilities.

Figure 8. Direct economic losses on physical systems, from fluvial floods: (a) total direct economic loss, (b) building structures, (c) building contents, (d) roads, (e) electrical facilities.

Figure 9. Direct economic losses to physical systems, from compound floods: (a) total direct economic losses, (b) building structures, (c) building contents, (d) roads, and (e) electrical facilities.