Extreme Temperature Events in China's Three Gorges Area
Deng, H., Zhao, F. and Zhao, X. 2012. Changes of extreme temperature events in Three Gorges area, China. Environmental and Earth Sciences 66: 1783-1790.
In an effort to address this question within the Three Gorges area of China, which comprises the Chongqing Municipality and the western part of Hubei Province, including the reservoir region of the Three Gorges Dam, Deng et al. used daily mean, maximum and minimum temperatures for the period 1958-2007 that they obtained from ten meteorological stations within this region to determine the number of hot days (HDs, at or above 35°C), very hot days (VHDs, at or above 38°C) and extremely hot days (EHDs, at or above 40°C). And defining a heat wave (HW) as a period with no fewer than three consecutive HDs, they defined a short heat wave (SHW) as being at least six days long, and a long heat wave (LHW) as a heat wave exceeding six days.
The three Chinese researchers report that over the course of their study period (1958-2007), their study area did indeed experience a mean annual warming trend, but with slight decreasing trends in spring and summer temperatures. They also say that extreme high temperature events showed a U-shaped temporal variation, decreasing in the 1970s and remaining low in the 1980s, followed by an increase in the 1990s and the 21st century, such that "the frequencies of HWs and LHWs in the recent yeas were no larger than the late 1950s and early 1960s." In fact, they indicate that "coupled with the extreme low frequency in the 1980s, HWs and LHWs showed a slight linear decreasing trend in the past 50 years." Put another way, they say that the most recent frequency of heat waves "does not outnumber 1959 or 1961," and that "none of the longest heat waves recorded by the meteorological stations occurs in the period after 2003."
In concluding their discussion of their findings, Deng et al. write that "compared with the1950s and 1960s, SHWs instead of LHWs have taken place more often," which change, as they describe it, "is desirable, as longer duration leads to higher mortality," citing Tan et al. (2007). And so it is that for the Three Gorges area of China, even a mean annual warming trend over the past half-century, has not led to an increase in the frequency of extremely long heat waves.
Tan, J., Zheng, Y. Song, G., Kalkstein, L.S., Kalkstein, A.J. and Tang, ZX. 2007. Heat wave impacts on mortality in Shanghai, 1998 and 2003. International Journal of Biometeorology 51: 193-200.