Spatial rainfall distribution

From Clive Best

Rainfall anomalies also have monthly spatial distributions analogous to those for temperature. North Atlantic storms in January 2014 brought flooding to Western England. That month’s distribution shows  that abnormally high rainfall also affected the western coastlines of France, Spain and Portugal, the Alps and Eastern Europe.

Here is an animation of average rainfall anomalies from Jan 2014 to March 2018. The distribution of abnormal “wet areas” is not random but  instead  flows with the seasons.

Only the darker blue spots are significantly wetter than the 30 year average (1961-1990). Light blue to yellow areas are all dryer than normal.

Finally we look at the old data from 1838 to 1860 which gives a strong positive ‘global’ rainfall anomaly in the annual data. The values are in reality very regional, as are those for temperature anomalies.

The early stations are sparsely distributed mainly in central Europe, US & Australia. They indeed show mainly positive rainfall anomalies. It would seem that these areas were indeed wetter then today, but just how reliable these trends are is unclear. Perhaps the rain gauges or procedures were less accurate than they are today.


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