Response of carbon and water fluxes to dryness/wetness in China

Carbon-water cycle of terrestrial ecosystem is the important process of energy and mass exchanges, which is greatly influenced by changes of wet/dry conditions. Recently, China is experiencing frequent extreme weather events. Many concerns have been raised to explore how and to what extent dryness/wetness have influenced the carbon-water cycle in China on the regional scale. In this study, we examined the effects of changes of dryness/wetness on gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) in terrestrial ecosystems of China during 2001 - 2013 using standardized wet/dry anomaly index and Mann-Kendall method. Our analysis indicated that droughts hit extensively in 2001, 2006, 2009, and 2011, in contrast, extremely severe floods occurred in 2002, 2003, and 2010. Spatially, droughts increased obviously in south China but were alleviated in north China from 2001 to 2013. On average, GPP and WUE of China exhibited increasing trends but ET exhibited a decreasing trend. Severe dry/wet conditions (|SPEI| > 1) decreased GPP, ET, and WUE. Furthermore, the effect of dry stress on GPP, ET, and WUE was much more serious than the effect of wet stress. It was implied that the trends of GPP, ET, and WUE would not change greatly on the long-term scale, but extreme dry/wet events would enhance their change amplitudes in future.