# Flash Floods Hazard to the Settlement Network versus Land Use Planning (Lublin Upland, East Poland)
## 3 Methods
### GIS Analysis  
The first step of the analysis was to identify buildings that are located on the line of potential episodic runoff; the next was to determine how susceptible the catchments of these runoffs are. Each municipality in Lublin Upland was studied in this way. However, as was mentioned before, for the detailed studies, ten municipalities with the highest building density threatened by the flash floods were chosen. A simple assumption was made: the greater the susceptibility of the catchment to episodic runoff (flash floods), the greater the threat to buildings located at the mouth of the catchment. In order to delineate the boundaries of catchments associated with settlement and potentially threatened by flash floods, it was first necessary to create flow direction and flow accumulation layers based on potential runoff lines (flowlines). It was assumed, following [PERSON] [18], that the minimum catchment area in which a flash flood can form in the Lublin Upland is 0.5 ha. The layer of flowlines was juxtaposed with the layer of buildings, and those that were no more than 2 m from the flowlines were selected. Then, on each flowline, the point closest to each building (pour point) was determined and used  
Figure 2: Workflow model of data processing and calculations. in the next step to determine the catchment that collects water flowing into the vicinity of the building. In many cases, the identified buildings lay along the same line of runoff, and the designated catchments overlapped. The procedure for dealing with these cases is explained later in the manuscript. In the next step, a slope layer (measured in degrees) and geomorphon map [57] were calculated from the DTM, which classifies the topography of the area into 10 main geomorphometric units (Figures 2 and 3). Detailed analyses were performed for 12,024 catchments covering a total of 339.96 km\({}^{2}\). It should be noted here that the catchment areas did not coincide with the boundaries of municipalities and often included areas beyond. Data processing and analytical procedures used geoprocessing models created in ArcGIS Pro 3.0. In the next step, the total area and area shares of forests were identified. Only catchments with an area of less than 10 km\({}^{2}\) and a forest share of less than 50% were included in the analyses. The possibility of rapid surface runoff was considered low for the large area occupied by the forest [8; 10; 12; 14]. At the same time, a limit on the catchment area was introduced to keep them comparable. In total, nine catchment parameters were evaluated  
location in topography to identify those associated with land depressions and concentrated runoff. * Slope of valley sides--steeper slopes and higher gradients increase susceptibility due to more surface runoff and water delivery to valley bottoms. * Catchment shape--the more circular the catchment area, the higher the susceptibility because water inflow to the valley floor is more spread out over time. * Slope of valley bottom--a more sloped valley bottom increases the susceptibility due to faster surface runoff. * Road density--higher road density increases the susceptibility because impermeable roads are places where surface runoff rapidly forms. * Local relief--higher relative heights increase susceptibility to faster surface runoff. Subsequently, the catchments were assigned points for each characteristic, using the criteria summarized in Table 2. Some of the features, due to their higher influence on the formation of flash floods, were given more weight by doubling the number of points (share of arable land, geomorphon type, and mean slope).