Improving Water Erosion Estimates for Iran

The amount of country's water erosion is estimated at a rate of 976 million t.yr-1 by Erosion Potential Method (EPM) based on the national erosion map prepared at the Soil Conservation and Watershed Management Research Institute. This map is suitable for identifying the most sensitive areas to erosion in each region, but the estimated values ​​of the model need calibration, which was estimated ​​based onthe observed sediment yield data of 276 watersheds. The minimum and maximum annual observed sediment yields were 4 and 5591t.km-2, and estimated by the model was 31 and 2946 t.km-2, respectively. Correction ratio in the eight homogeneous regions was between 0.57 to 1.43 by dividing the median of the observed sediment yields to the corresponding ​​estimates in the studied watersheds. These ratios then were used to improve the erosion values ​​for homogeneous regions between 1063 and 130 t.km-2.yr-1, belonging to the Oman Sea (Region 8) and the internal desert (Region 6) basins, respectively. The annual erosion of the country was estimated to be million 895 t.yr-1. The(5.5 t.ha-1.yr-1), with the highest and lowest contribution, respectively to the Region 8 (33%) and the Region 1 or Caspian Sea coastal basins (2.5%). It was also found that the observed specific sediment yield had a positive correlation with an increasing area unlike the expectation, with its probable reasons have been explained in the paper.