Relationship between Soil Moisture and Vegetation Activity in the Mongolian Steppe

Abstract

Drought has become widespread throughout the Northern Hemisphere since the mid-1950s, affecting the Mongolian steppe and pastureland used for livestock. Given this background, we investigated the relationship between modeled root-zone soil moisture (Wm) and vegetation activity based on Normalized Difference Vegetation Index (NDVI) data for the Mongolian steppe during the period 1982-2005. In general, interannual change in NDVI coincided with that in Wm. NDVI showed a stronger correlation with Wm (r = 0.91) than with precipitation (P) (r = 0.65). A strong positive correlation was found between seasonal changes in NDVI and above-ground biomass (r = 0.94).A comparison between years with high and low NDVImax revealed that the significant difference in P led to a significant time-lagged (about a half month) difference in Wm and finally to that in NDVI with time lags of about one month. In addition, NDVImax value of a given year was correlated with the Wm value for the current year (r2 = 0.53), and was more strongly correlated with the combination of the current year Wm and the preceding year NDVImax of (r2 = 0.55). This result suggests that on the interannual basis, the vegetation activity is primarily controlled by the current year soil moisture and slightly affected by underground structures stored in the root system.