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The soil loss caused by rainfall-runoff process is a global issue which can decrease the lands fertility and increase the flood hazards. There are many different empirical relationships and numerical methods available for soil loss estimation. One of the most commonly used methods is the Universal Soil Loss Equation (USLE), which is widely used to estimate the amount of annual rill erosion. The main aim of this paper was to evaluate the accuracy and applicability of the USLE method in the estimation of soil loss in elevated and rocky mountainous areas of Tibetan plateau. To do this, some of the observed and modeled soil loss data that were available in some Chinese researches, were selected. Land slope, soil type, land cover, Normalized Difference Vegetation Index (NDVI), aspect, monthly and annual rainfall and runoff maps from GIS were derived and investigated to calculate the USLE parameters. The results showed that the accuracy of the USLE model was decreased significantly in regions with high soil loss risk due to ignoring the rock properties and snow cover in K parameter. Also, the results showed that parameters which can decrease the soil loss significantly such as rock fragments content and low height vegetation have to be considered in NDVI calculation. Hence, it is recommended to improve the accuracy of the model by adjusting C factor for elevated mountainous areas based on the rock properties and snow cover which can be derived from the remote sensing maps. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to evaluate the impact of land cover resolution, in comparison with the digital elevation model (DEM) resolution, on hydrological modeling outputs. Three different basins in the various resolutions of DEM (12.5, 25, 50, 100, 500 and 1,000 m) and land-use maps (250, 1,000 and 2,500 m) were collected in this study, and the hydrological modeling process was performed using the Soil and Water Assessment Tool (SWAT) model. The soil type resolution was 1,000 m for all basins, and the runoff modeling was done based on the Soil Conservation Service Curve Number (SCS-CN) method. The final model outputs showed that the DEM cell size variations affect significantly the topographical characteristics of a catchment such as area, mean slope, river network and time to concentration which alter the flood modeling outputs especially in hilly watersheds (mean slope more than 15%) up to 15% for a DEM cell size of 1,000 m in comparison to 12.5 m. Also, the resolution and spatial distribution of land cover maps which directly specify SCS-CN values, can change the output simulated runoff results up to 49% for a land cover cell size of 2,500 m in comparison to 250 m. These results indicated that the quality of the land cover map is more important than the quality of DEM in hydrological modeling. Also, the results showed that for an identical land-use cell size, the differences between model outputs using DEM cell sizes less than 100 m were not very significant. Furthermore, in all models by increasing the DEM cell size, the simulated runoff depth was decreased. [ABSTRACT FROM AUTHOR]