Morteza Behzadfar, Hamid Reza Moradi, Seyed Hamid Reza Sadeghi,
Volume 12, Issue 3 (1-2005)
Abstract
This study tries to investigate relationship between rainfall parameters and USLE R factor. To gain R-factor, at first, shower kinetic energy was calculated and then its erosivity computed by using maximum 30 minutes rainfall intensity. Therefore 3 meteorological stations in Khuzestan province and one station per Kohgiloyeh & BoyerAhmad and Boushehr provinces were selected and their recorded hyetographs of 13 years were analyzed. For any hyetographs, rainfall erosivity was computed in any one month, season, or year and corresponding rainfall parameters were extracted too. Temporal and spatial variation of rainfall erosivity was studied and relationships between R factor and rainfall characteristics were investigated by using regression analysis. It was resulted that February to March and winter season has the most erosivity risk. Spatial analysis of rainfall erosivity in selected area showed that Dezful and Ramhormuz have the maximum erosivity factor. Mean annual erosivity factor of Khuzestan province was computed 28.07 ton.m/ha.h. Regression analysis showed strong relationships between rainfall amount (mm) and maximum 30 minutes rainfall intensity (cm/h) with R factor. A model that computes R-factor by means of rainfall amount was suggested.
Volume 13, Issue 3 (5-2011)
Abstract
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 18 synoptic stations of the Iranian
Meteorological Organization, known to have reliable data and hyetographs with a 23 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 0.228, 0.201, and 0.147 MJ mm ha-1 h-1, respectively, while June and
August had the lowest erosivity factors, as indicated by R factors of 0.017 and 0.027 MJ
mm ha-1 h-1, 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 11.518 and 4.260 MJ mm ha-1 h-1, 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 0.201 and 0.212 MJ mm ha-1 h-1, respectively.
The long term mean annual rainfall erosivity factor of Iran was ultimately found to be
1.226 MJ mm ha-1 h-1.
