TY - JOUR T1 - Optimization of Export Coefficient Model Based on Precipitation and Terrain Impact Factors TT - بهینه‌سازی مدل انتقال آلودگی غیرنقطه‌ای بر اساس ضرایب توپوگرافی و پراکندگی بارش JF - Geographical-Researches JO - Geographical-Researches VL - 36 IS - 4 UR - http://georesearch.ir/article-1-1105-en.html Y1 - 2021 SP - 337 EP - 346 KW - Export Coefficient Model KW - Non-Point Pollution KW - Precipitation Impact Factor KW - Terrain Impact Factor N2 - Aims: Very serious studies have been carried out on the Chinese Tibetan Plateau due to the high level of erosion in this region all over the world. Changes in soil nitrogen and phosphorus parameters are followed by estimating soil erosion. Therefore, the purpose of this study was to investigate the effect of two parameters of basin topography coefficient and precipitation distribution on pollution load transfer using an experimental transfer coefficient model. Methodology: In this study, which was conducted in 2019, a part of the Tibetan Plateau was selected where proven data on agricultural pollution such as nitrogen and phosphorus were available. This study was part of an integrated water resources management project conducted jointly between Iran and China. The results of estimating the estimated non-point pollution by the experimental model of transfer coefficient and the optimized model by applying alpha and beta coefficients were evaluated with the measured data. These two coefficients are among the key parameters in non-point modeling of pollution because they cause the role of land features and the non-uniformity of precipitation in the model to be considered. Findings: Analysis of the Export Coefficient Model outputs together with the modified Export Coefficient Model outputs and comparing the results with observed data showed that the application of alpha and beta coefficients was very effective to increase the accuracy of the model. The relative error between amount of nitrogen which was estimated by the modified Export Coefficient Model and the measured values was reduced comparing to the results of Export Coefficient Model without using the coefficient: for station 1, 12% and 34% in 2007 respectively; and 18% and 20% in 2015 respectively; for station 2, 16% and 30% in 2007 respectively; and 21% and 34% in 2015 respectively. Conclusion: This study illustrated that the modified Export Coefficient Model could provide more accurate results in comparison with the Export Coefficient Model and would be useful in decision making and planning processes in large-scale agricultural watersheds in which, pesticides are the most important pollution sources for surface and sub-surface water. M3 ER -