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Placing the 2013 Summer Drought of Southern China in the Proper Perspective

Paper Reviewed
Zhao, Y., Shi, J., Shi, S., Yu, J. and Lu, H. 2017. Tree-ring latewood width based July-August SPEI reconstruction in South China since 1888 and its possible connection with ENSO. Journal of Meteorological Research 31: 39-48.

In 2013, a severe summer drought occurred in southern China, affecting over 80 million people living in ten provinces. The drought was severe enough to cause widespread crop failure and resulted in economic losses of 59.0 billion Yuan (Hou et al., 2014). Not surprisingly, it might be very tempting for some to consider the occurrence of this drought a fingerprint of CO2-induced global warming, as one of the premiere tenants of global warming theory is that droughts should be becoming more frequent and more severe. So might the great 2013 summer drought of southern China indeed be a fingerprint of global warming?

The answer to this question can be gleaned from the recent study of Zhao et al. (2017). Recognizing that "our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of meteorological records," the team of five Chinese scientists derived a new summer hydroclimate reconstruction for the region for the period 1888 through 2014. In accomplishing their objective, they used tree-ring latewood width chronologies from fourteen Tsuga longibracteata trees near Qishanzhai, China (26.23°N, 110.23°E) to reconstruct a summer (July-August) standardized precipitation-evapotranspiration index (SPEI) over the past 127 years. The resultant series is presented in the figure below.

As indicated in the figure, there were a number of extremely wet and dry summers (defined as 1.5 standard deviations from the mean, the dotted horizontal lines on the image) in the record. Years defined as extremely dry included 1900, 1911, 1926, 1928, 1934, 1935, 1957, 1972 and 2013, whereas extremely wet years included 1915, 1923, 1931, 1941, 1948, 1955, 1970 and 1973. Specifically commenting on the magnitude of the 2013 drought, Zhao et al. state that "it is not unusual because more extreme drought events occurred in the first half of the 20th century," including -- in order of severity -- the 1926, 1934, 1935 and 1900 droughts.

Consequently, it is clear that the 2013 severe summer drought of southern China was neither unusual nor unprecedented, and therefore highly unlikely to be a fingerprint of global warming.


Figure 1. Reconstructed July-August SPEI with its 10-yr low-pass filter (gray line). The dashed line represents the mean value of the reconstruction and the dotted lines represent ± 1.5 standard deviations from the mean. Source: Zhao et al. (2017).

Reference
Hou, W., Chen, Y., Li, Y., Wang, Y., Wang, Z., Zhu, X., Zhou, B.,Ye., D., Zhao, S., Cai, W., Yin, Y., Zhong, H., and Zhao, L. 2014. Climatic characteristics over China in 2013. Meteorological Monthly 40: 482-493 doi: 10.7519/j.issn.1000-0526.2014.04.011. (in Chinese)

Posted 30 Jun 2017