Index of aspect is derived from the elevation that defines the pixel directions per unit degree, allowing for more precise flood risk mapping judgments. It is often referred to as the horizontal direction of the mountain facing, and it determines the local climatological conditions. Aspect of the catchment was ranged from −1 to 360 (Figure 3(i)). It was divided into the following five categories: –1 to 75, 76–150, 160–220, 230–280, and 290–360 (Table 11).