Impact of Different Yearly Rainfall Patterns on Dynamic Changes of Soil Moisture of Fixed Sand Dune in the Horqin Sandy Land

Abstract

The in-situ monitoring method was used for studying the spatio-temporal variation of soil moisture in the growing season of different precipitation years in fixed dunes of Horqin Sandy Land. The results showed that different precipitation years have a certain influence on both seasonal variation and vertical variation of soil moisture in the fixed dunes of the study area. (1) During the normal year, the seasonal variation of soil moisture was relatively flat. During the dry year, the soil moisture gradually decreased before the rainy season and increased significantly after the rainy season. During both normal and dry years, heavy rainfall can significantly recharge the soil moisture content in all soil layers. During the wet year, the rapid recharge effect of soil moisture from heavy rainfall in the shallow layer was better than that in the deep layer. (2) During the normal and wet years, the soil moisture was at a relatively low level in May and changed little with the soil depth. In different months of other precipitation years, the soil moisture changes with soil depth all showed the trend of “first increase, then decrease, and finally slow increase”. Higher soil moisture were generally in the soil layer of 30∼70 cm, the soil moisture below 70 cm changed little with the soil depth and tended to be stable below 110 cm. (3) Under the influence of heavy rainfall, the vertical variation of soil moisture tended to be active in the wet year, showing three variation layers, i.e. quickly changing layer, active variable layer and sub-active variable layer. During the normal and dry years, the soil moisture showed small vertical changes, and it was divided into only two layers. For the dry year, only the surface layer showed active variation of soil moisture; for the normal year, the soil layer above 70cm showed active variation of soil moisture.