*3.2. Flash Flood Conditioning Factors*

In this study, nine flash flood affecting parameters, namely distance from river, aspect, elevation, slope, rainfall, distance from faults, soil types, land use, and lithology were considered in the modeling. Thematic maps were generated using ArcGIS 10.1, ENVI 5.1, and SAGA-GIS 2 software (Figure 3). All these maps were converted to raster image (format) of 12.5 m × 12.5 m pixel size, which is up to the resolution of DEM for model studies (Table 1). A detailed description of these factors is given below:



**Figure 3.** *Cont.*

**Figure 3.** Maps of flash flood conditioning factors: (**a**) distance to rivers, (**b**) aspect, (**c**) elevation, (**d**) slope, (**e**) rainfall, (**f**) distance from faults, (**g**) land use, (**h**) soil, and (**i**) lithology.

#### Distance from rivers:

In general, the area which is close to the rivers is more prone to flooding in both cases of normal flood and flash flood within the river basin as water flows from higher elevation and accumulates at lower elevations. The areas close to other terrestrial water bodies such as ponds, dams, and lakes are also likely to be flooded in the event of heavy rains as the terrain in the vicinity of these water bodies would be almost flat [46]. However, pluvial flash floods may also occur at a distance away from the water bodies depending on the meteorological and topographical conditions. In the present study, six classes of buffer have been developed at buffer distance of 100 m from the river (Figure 3).

Aspect:

An aspect map of a region represents the direction of the surface slope. The direction which a slope faces with respect to the sun (aspect) has a profound influence on microclimate. The aspect map also shows no slope area (flat) where no surface slope is present; this is generally at the base of the hills or near lakes. Regions with low slope or regional flat surface are more vulnerable to the flash flood where water accumulates and rises [6,47]. Therefore, by using this parameter, the flat regions can easily be identified. Besides, flat area flooding also depends on the monsoon wind direction which hits the surface slope (Aspect). In this study, the aspect map was generated from the DEM with nine classes (Figure 3).
