Spatial and Temporal Variations in the Rainfall Erosivity Factor in Iran

Accelerated soil erosion is an undesirable process that adversely affects water and soil resources. Rainfall erosivity is an important factor in water erosion models. Accordingly, the present study was conducted to estimate the rainfall erosivity throughout Iran based on the latest available detailed rainfall data while considering its temporal and spatial variations. To accomplish this, the data from ۱۸ synoptic stations of the Iranian Meteorological Organization, known to have reliable data and hyetographs with a ۲۳ year common period, were accordingly analyzed. The kinetic energy of rain for each storm event was calculated based on Wischmeier and Smith’s original model, i.e. the USLE, and many of its modifications. Later, the rainfall erosivity factor was calculated on a monthly, seasonal, and annual basis using the calculated kinetic energy. The results revealed that the greatest risk of erosivity occurred in March, December, and November, as indicated by R factors of ۰.۲۲۸, ۰.۲۰۱, and ۰.۱۴۷ MJ mm ha-۱ h-۱, respectively, while June and August had the lowest erosivity factors, as indicated by R factors of ۰.۰۱۷ and ۰.۰۲۷ MJ mm ha-۱ h-۱, respectively. Furthermore, analysis of the spatial variations in R verified that the Anzali and Babolsar Stations, located in northern Iran, had the maximum erosivity values, with R factors of ۱۱.۵۱۸ and ۴.۲۶۰ MJ mm ha-۱ h-۱, respectively. Conversely, the Bam and Semnan Stations, located in the central and eastern Iran, had the minimum erosivity values, as indicated by R values of ۰.۲۰۱ and ۰.۲۱۲ MJ mm ha-۱ h-۱, respectively. The long term mean annual rainfall erosivity factor of Iran was ultimately found to be ۱.۲۲۶ MJ mm ha-۱ h-۱.

Keywords:

IRAN , USLE , Rainfall Erosivity , Smith Method , Soil erosion , Wischmeier