Wang, A., Lettenmaier, D.P. and Sheffield, J. 2011. Soil moisture drought in China, 1950-2006. Journal of Climate 24: 3257-3271.
What was done
Utilizing the multi-model approach developed by Wang et al. (2009), the authors employed four physically-based land surface hydrology models that were driven by an observation-based three-hourly meteorological data set to simulate soil moisture over China for the period 1950-2006, deriving monthly values of total column soil moisture from which they calculated agricultural drought severities and durations.
What was learned
Wang et al. report that "for drought areas greater than 150,000 km2 and durations longer than three months, a total of 76 droughts were identified," and they say that "regions with downward trends were larger than those with upward trends (37% versus 26% of the land area)," implying that "over the period of analysis, the country has become slightly drier in terms of soil moisture." So what does this imply about the future?
What it means
The three researchers write that the "trends in drought severity, duration and frequency suggest that soil moisture droughts have become more severe, prolonged and frequent during the past 57 years, especially for northeastern and central China, suggesting an increasing susceptibility to agricultural drought." However, climate alarmists need not be too alarmed over this finding, for Wang et al. additionally state that "climate models project that a warmer and moister atmosphere in the future will actually lead to an enhancement of the circulation strength and precipitation of the summer monsoon over most of China (e.g., Sun and Ding, 2010) that will offset enhanced drying due to increased atmospheric evaporative demand in a warmer world (Sheffield and Wood, 2008)."
Also providing some "worry relief" are the contemporary findings of Tao and Zhang (2011), who -- using the Lund-Potsdam-Jena Dynamic Global Vegetation Model -- concluded that the net effect of physiological and structural vegetation responses to expected increases in the air's CO2 content will lead to "a decrease in mean evapotranspiration, as well as an increase in mean soil moisture and runoff across China's terrestrial ecosystem in the 21st century," which should be good news, indeed, for the world's most populated country.
Sheffield, J. and Wood, E.F. 2008. Projected changes in drought occurrence under future global warming from multi-model, multi-scenario, IPCC AR4 simulations. Climate Dynamics 31: 79-105.
Sun, Y. and Ding, Y.-H. 2010. A projection of future changes in summer precipitation and monsoon in East Asia. Science in China Series D: Earth Sciences 53: 284-300.
Tao, F. and Zhang, Z. 2011. Dynamic response of terrestrial hydrological cycles and plant water stress to climate change in China. Journal of Hydrometeorology 12: 371-393.
Wang, A., Bohn, T.J., Mahanama, S.P., Koster, R.D. and Lettenmaier, D.P. 2009. Multimodel ensemble reconstruction of drought over the continental United States. Journal of Climate 22: 2694-2712.Reviewed 14 September 2011