Simulating long-term soil water balance in response to land use change in the Northern China's Loess Plateau

To explore the impact of land-use change on the long-term soil water balance in Northern China's Loess Plateau, we used the Hydrus-1D model to simulate the soil water dynamics at depths of 0—4 m under the scenario of arable land-alfalfa land-natural grassland located in the Liudaogou watershed. The evolution characteristics of hydrological variables including soil water storage, deep seepage and evapotranspiration were quantified from 1981 to 2050. The results showed that soil water fluctuated with rainfall levels during arable land periods, with 88% of the annual precipitation consumed through evapotranspiration, and 11% was lost to deep seepage. The first stage of soil water change during the alfalfa land period was 1—6 years after plantation, during this period, evapotranspiration accounted for 108% of the annual rainfall, leaving the soil water in a negative balance. And the soil water storage of 0—4 m decreased at a rate of 52 mm/a. The second stage was 7—13 years after plantation, almost all rainfall was consumed by evapotranspiration. Eight years after alfalfa land transitioned into natural grassland, annual evapotranspiration decreased by 31%, and soil water storage gradually recharged at 45 mm/a. Subsequently, 92% of the annual rainfall was used for evapotranspiration, with the remaining 8% was lost to deep seepage. The soil water remained in a relatively stable state. These indicated that the soil water balance modes varied under different vegetation types. Planting vegetation with high-water-consumption could cause negative balance of soil water and led to serious soil desiccation, which then had a negative effect on soil water supply. However, the formed dry soil layer could be completely restored by changing the vegetation type.