Multi-Decadal Soil Moisture Trends in Mongolia and Their Relationships to Precipitation and Evapotranspiration

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 (Wm) 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 (Wo). 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 Wm 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 Wm 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 Wm 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 (1.8–3.0 months). These findings indicate that Wm 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. Keywords: evapotranspirationpastureprecipitationsoil moisturesteppewater balance model Acknowledgement The authors are deeply indebted to the Institute of Meteorology, Hydrology and Environment of Mongolia, who provided the soil moisture and meteorological data used in this study. Notes *Significant at 5% level. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/uasr.