Soil moisture-based study of the variability of dry-wet climate and climate zones in China

An ensemble soil moisture dataset was produced from 11 of 25 global climate model (GCM) simulations for two climate scenarios spanning 1900 to 2099; this dataset was based on an evaluation of the spatial correlation of means and trends in reference to soil moisture simulations conducted using the community land model driven by observed atmospheric forcing. Using the ensemble soil moisture index, we analyzed the dry-wet climate variability and the dynamics of the climate zone boundaries in China over this 199-year period. The results showed that soil moisture increased in the typically arid regions, but with insignificant trends in the humid regions; furthermore, the soil moisture exhibited strong oscillations with significant drought trends in the transition zones between arid and humid regions. The dynamics of climate zone boundaries indicated that the expansion of semiarid regions and the contraction of semi-humid regions are typical characteristics of the dry-wet climate variability for two scenarios in China. During the 20th century, the total area of semiarid regions expanded by 11.5% north of 30 degrees N in China, compared to the average area for 1970-1999, but that of semi-humid regions decreased by approximately 9.8% in comparison to the average for the period of 1970-1999, even though the transfer area of the humid to the semi-humid regions was taken into account. For the 21st century, the dynamics exhibit similar trends of climate boundaries, but with greater intensity.