Background Tuwei river watershed is one of the most serious soil loss and fragile district of ecology in the middle reaches of the Yellow River, which is located in the windy desert region of the north Shaanxi province. The harsh natural environment has greatly done threat to the sustainable development. In order to improve the ecological environment, Chinese government has implemented the Grain for Green policy since 1999.

Methods In order to explore the spatiotemporal evolution of soil erosion before and after Grain for Green Project in this area, USLE model, Remote Sensing (RS) and Geographic Information Systems (GIS) were accepted to analyze soil loss. Three remote sensing images of 1988, 200 and 2013 was interpreted in ENVI 5.2, and rainfall, topography, land use type and vegetation cover data were analyzed in ArcGIS 9.3. Universal Soil Loss Equation (USLE) was used to estimate a series of soil erosion modulus from 1988 to 2013.

Results 1) The rainfall erosivity increased significantly from 2001 to 2013 and from 1988 to 2000, and the vegetation cover of C factor decreased by about 0.29 in past 26 years. The soil erosion intensity in the watershed showed a gradual increase from upstream to downstream.2)The soil erosion has an obviously decreased tendency, whatever in the area or the intensity. The R factor was approximately equivalence in 1988 and 2013, however, corresponding soil erosion modulus respectively were 12 434.47 t/(km²·a) in 1988 and 3 721.08 t/(km²·a) in 2013, respectively. The total soil loss in 1988 was 43.76×10⁶ t, while it sharply decreased by 68.33% in 2013(13.1×10⁶ t). Compared the soil loss in 1988, 2000 and 2013, it was a reducing trend with the increasing of elevation, but incremental tendency with slope. Compared with 1988, the average soil erosion modulus in 2013 in different slope rapidly decreased. It reduced 6 712.31 t/(km²·a), 7 668.51 t/(km²·a), 6 712.31 t/(km²·a), 8 885.27 t/(km²·a), 5 375.43 t/(km²·a), and 23 357.46 t/(km²·a) in 0°-5°, 5°-8°, 8°-15°, 15°-25° and over 25°, respectively. The descending order of soil erosion intensity in different land use was unused land, grassland, forestland and cropland, so the benefit of soil and water conservation was the most obvious in unused land and grassland.

Conclusions  The soil erosion value estimated by USLE model combined with RS and GIS was smaller than the observed value in Tuwei river watershed. Yet despite all that, the assessment soil loss value is credible results. This method is feasible to assess soil erosion in such areas. In the recent 26 years, with the rapid recovery growth of grass and forest in the Tuwei river watershed, the soil and water conservation has achieved significant benefits. It has really reflected the temporal and spatial changes of soil erosion, which can be a reference for the local government to take measures to manage soil loss in the future.