干旱区生态环境知识资源中心

Multi-decadal soil moisture trends and their relationships to precipitation (P) and evapotranspiration (E) were explored in Mongolia. We modified a simple soil-moisture model intended for use in a wide range of practical applications for monitoring of pasture drought across the country, by incorporating soil freezing and snow melt. Daily soil moisture (W-m) was simulated using the model during 1961-2006 at nine stations distributed in the three different vegetation zones: forest steppe (FS), steppe (ST), and desert steppe (DS). The model performed reasonably well in simulating seasonal and interannual variations in observed soil moisture (W-o). The Wm was controlled by the subtle balance between P and evapotranspiration (E), which had in turn impacted on the vegetation during the growing season (May-September). All vegetation zones showed a decreasing trend in W-m during 1961-2006 due to decreased P and increased potential evapotranspiration, although the drying trend was only significant (p <0.05) in the FS. Composite analyses revealed that W-m anomalies were most manifested in summer due to large P and E anomalies, which were maintained throughout the freezing of winter into spring. In addition, autocorrelation analysis of W-m for the FS zone showed that during the autumn and winter, the temporal scale was 6.0-7.0 months larger than during spring and summer (1.8-3.0months). These findings indicate that W-m acts as an efficient memory of P anomalies via freezing of the soil and as an initial moisture condition for vegetation activity in the subsequent year.