Background
Climate alarmists contend that various types of extreme weather events become both more frequent and more extreme as the world warms; and the authors write, in this regard, that "hail is one of the most extreme weather phenomena, causing great loss to agriculture every year in China (Han, 1999)." Hence, they decided to see if this particular weather phenomenon had gotten any worse throughout China over the period of time during which climate alarmists claim the planet's mean surface air temperature rose at a rate and to a level that was unprecedented over the past one to two millennia.

What was done
Xie and Zhang first noted that Xie et al. (2008) had already found there was a "significant decreasing trend of hail frequency in most of China from the early 1980s based on 46 years of data during 1960-2005." So for this vast country, they began with the knowledge that one of two types of potential hail extremeness (hailstorm frequency) had not lived up to climate-alarmist hype. Therefore, the two researchers focused on the other type of extremeness (hailstone size), noting that "changes in hail size are also an important aspect of hail climatology," and they went on to study the long-term trend of hail size in four regions of China over the period 1980-2005, using maximum hail diameter data obtained from the Meteorological Administrations of Xinjiang Uygur Autonomous Region (XUAR), Inner Mongolia Autonomous Region (IMAR), Guizhou Province and Hebei Province.

What was learned
Xie and Zhang report that their work revealed an uptrend in maximum hail diameter in Hebei, a flat trend in XUAR, and a slight downtrend in both Guizhou and IMAR; but they add that "none of the trends is statistically significant."

What it means
In light of these several findings, it seems pretty clear that the highly-hyped global warming of the past few decades has led to no increase in the extremeness of Chinese hail storms. In fact, the data suggest there was a slight decline in the frequency of such storms, along with a hint of a possible decrease in maximum hail diameter, which non-significant latter observation doesn't mean too much, except that it strongly suggests there was at least no increase in maximum hail diameter.

References
Han, G.F. 1999. The analysis on the feathers of hail hazard in Hebei province. Journal of Catastrophe 14: 243-246.

Xie, B., Zhang, Q. and Wang, Y. 2008. Trends in hail in China during 1960-2005. Geophysical Research Letters 35: 10.1029/2008GL034067.