**4. Spatial estimation of soil erosion**

### **4.1 The R factor**

R factor determines erosivity by rainfall at a specific region, which is usually based on the intensity and amount of precipitation. It mainly represents the impact caused by rainfall intensity on soil erosion. In this study area, the monthly precipitation data for six weather stations situated in the study area were obtained from the World Bank website. It was validated with the satellite based data to integrate the results. Rainfall map was prepared which represents the spatial distribution of rain in the Eastern Hindukush. This map was utilized to estimate R factor map by calculating the Rainfall erosivity for a time period of about 1991 to 2019 in study area. Rainfall-runoff erosivity was calculated by the following equation used by many researchers on areas where similar topographic and atmospheric conditions prevail (**Figure 4**) [19, 22].

$$\mathbf{R} = \mathbf{0}.\mathbf{0}5 \times \mathbf{P}.\tag{14}$$

**Figure 4.** *Rainfall-Erosivity factor (R) of eastern Hindukush, Pakistan.*

Where, R = Rainfall Erosivity Factor, P = Mean Annual Rainfall in (mm).
