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35 Years of Hail Frequency and Intensity Records for China

Paper Reviewed
Ni, X., Zhang, Q., Liu, C., Li, X., Zou, T., Lin, J., Kong, H. and Ren, Z. 2017. Decreased hail size in China since 1980. Scientific Reports 7: 10913, DOI:10.1038/s41598-017-11395-7.

Climate models typically predict CO2-induced global warming will increase the frequency and severity of thunderstorms. Consequently, hail frequency and intensity are also expected to rise in the future.

A test of this model-based hypothesis was recently performed by Ni et al. (2017) for China. Using data from 2,254 locations that they obtained from the Chinese National Meteorological Information Center, the eight researchers examined trends in both the occurrence of hail days (frequency) and the mean size of hail (intensity) over the period 1980-2015.

In discussing their findings, Ni et al. report that probability density function (PDF) analyses revealed there was "a clear shift" in hail sizes between the early (1980-1997) and latter (1998-2015) half of the record, where the probability of small hail sizes (<5 mm) increased, whereas for larger sizes (>20 mm) it decreased. Time series of hail parameters confirmed the PDF findings. Consistent with the increased probability of small hail sizes in recent years determined by PDF, Figure 1 (panel a-c) shows that the proportion of all hail events with sizes greater than or equal to 5, 10 and 20 mm has significantly decreased over the past 35 years.

Also shown in Figure 1 is a time series of the annual mean size of hailstones during hail events at all 2,254 stations where the hail size was ≥20 mm (panel d). This parameter has declined by a statistically significant 1.7 mm per decade. Because hail-induced property damage is mainly derived from large hailstones of 20 mm or more, this suggests there may well have been an alleviation of hail-induced property damage over the past three and a half decades. Similarly, trends in hail events with hail sizes of ≥10 mm also declined over the period of record, albeit at a smaller 0.7 mm per decade rate (panel d).

In light of all the above, Ni et al. conclude that these observational changes "imply a weakened [frequency and] intensity of hailstorms in China in recent decades." And that finding does not bode well for climate models, which predict that just the opposite should be occurring.


Figure 1. Time series of hail size parameters. (a) Interannual variations of the proportion of all hail events with hail size ≥5 mm over plateau, foothill, and plain regions of China; (b) same as (a) but for the proportion of all hail events with hail size ≥10 mm; (c) same as (a) but for the proportion of all hail events with hail size ≥20 mm; (d) annual mean size of hailstones in hail events with hail size ≥20 mm at all 2,254 stations; (e) same as (d) but for hailstones in hail events with hail size ≥10 mm. Source: Ni et al. (2017).

Posted 14 February 2018