The response of soil moisture to rainfall event size in subalpine grassland and meadows in a semi-arid mountain range: A case study in northwestern China's Qilian Mountains

摘要

Knowledge of soil moisture is critical to understanding many of the hydrological processes that are of interest in soil hydrology, meteorology, and ecology research. In the present study, we used rainfall and soil moisture data from 2003 to 2008 measured at grassland and meadow sites in the Qilian Mountains of northwestern China to analyze the response of soil moisture to rainfall event size during the growing season. The responses of soil moisture at the grassland and meadow sites to rainfall event size were similar, although total rainfall, the frequency of large rainfall events, and the vegetation types were different. Soil moisture at depths of 20 and 40. cm increased significantly after rainfall events larger than 15 and 20. mm, respectively, but the magnitude of these changes varied in response to differences in the duration of the dry interval preceding the rain. Soil moisture at depths from 60 to 80. cm in the grassland increased obviously with rainfall events larger than 40 mm or after two consecutive large rainfall events, but was not significantly correlated with rainfall event size in the meadow. Soil moisture at depths from 120 to 160. cm did not change significantly during the growing season at either site. The soil water storage at depths from 20 to 80. cm at both sites increased obviously after rainfall events larger than 20. mm. The present results suggest that large rainfall events (>20. mm) play a key role in increasing soil water storage in the grassland and meadow ecosystems of these semi-arid mountains.