Modeling the effects of crust on rain infiltration in vegetated sand dunes in arid desert

Shapotou Desert Research Station is located at the southeast edge of Tengger Desert in China. Shapotou sand dunes have been vegetated to stabilize them. The vegetated dunes have been completely covered by a natural crust. Rain infiltration was reduced by 36% to 74% on the crusted site while there was no reduction of rain infiltration on the sandy site. The infiltration rate was positively correlated with total rainfall and negatively correlated with rain intensity. Runoff on the crusted site provided water for vegetation growth in the hollows between sand dunes. The crust significantly impeded increased soil moisture. To increase soil moisture in the surface 40 cm layer, rainfall had to be above 8.5 mm on the slopes of sand dunes on the crust site, and increased with rain intensity. In the Shapotou area, the amount of rainfall that vegetation on slopes of sand dunes could utilize, was reduced to about 40 mm per year by the crust, although the mean annual precipitation was approximately 180 mm. It is expected that vegetation cover will continuously degrade in the future. To maintain vegetative cover adequate to stabilize the active sand dune, it was necessary to break part of the crust at slope of sand dune.