We continue our review of the latest published assessment of worldwide indicators of extreme weather, this week turning to the discussion of extreme precipitation. The authors present evidence that there has been a gradual increase in total precipitation worldwide since 1900. And then they ask if this has translated into an increase in extreme rainfall events. The answer is... it depends where you look. In most regions around the world, some monitoring stations show an increase, some a decrease, and most no change. One global study examined data covering 1964 to 2013 at 8,730 locations. 13% showed an increase, 10% showed a decrease and the rest (77%) showed no change. A more recent study covering 1950 to 2018 found 9% showed an increase, 2% showed a decrease and 89% showed no change. But within their data they found considerable regional variation.
The findings were summarized in the following chart:
For each location green indicates the percentage of stations showing no change, red denotes the percentage reporting and increase and blue the percentage reporting a decrease. Most places exhibit no trend, and in the specific locations with trends there are typically more exhibiting an increase than a decrease. The authors conclude:
Our review shows that while an increase in total annual precipitation is observed on a global level, an increase in extreme precipitation is observed for a limited number of stations and with strong regional differences. The absence of generalized growth trends in extreme precipitation can be explained by the fact that the genesis of extreme precipitation requires (1) the presence of a relevant source of moisture in the boundary layer, (2) morphology of the relief, circulatory structures at different scales and vertical thermal profile favourable to the rising of air mass with development of clouds of sufficient thickness (e.g. cumulonimbus and nimbostratus clouds) and (3) microphysical characteristics of cloud environment favourable to magnify droplets or ice crystals to give precipitation.