English Summer Rainfall Trends
By Paul Homewood
The Met Office has just announced that last month was the wettest June on record back to 1910, while July has started with more heavy rain. Is this just another example of the variability of English weather, or is it part of a longer term trend?
The Met Office graph in Figure 1 shows a clear cut change to drier summers around 1960, followed by a return to earlier levels in the last decade or so. The Met Office also keep records going back to 1766 for England & Wales, (but not Scotland), and these give quite a bit of extra information.
1) As seen in Figure 1, the long term trend has been towards drier summers since 1766.
2) Since 1970, though, the trend has been towards wetter summers.
3) As figure 4 shows, most of the wettest summers occurred in the earlier part of the record. Only one of the top twenty wettest summers has occurred since 1956, which was in 2007. The three wettest years were 1912, 1879 and 1829.
DEFRA Climate Projections
Earlier this year DEFRA, the UK’s Department for Environment, issued its “Climate Change Risk Assessment”, which projected a “change in average summer rainfall volumes ranging from a decrease of about 60% to an increase of about 10%” by the 2080’s. (It also forecast an increase in winter rainfall, which has been declining in recent years).
Perhaps they should take another look at their models.
The Met still insist on using the period 1971-2000 for their climate averages. (I currently have an FOI request asking them when they will change to 1981-2010, or if not, why – according to their website – The World Meteorological Organization (WMO) requires the calculation of averages for consecutive periods of 30 years, with the latest covering the 1961–1990 period. However, many WMO members, including the UK, update their averages at the completion of each decade. Thirty years was chosen as a period long enough to eliminate year-to-year variations.)
Often this can be extremely misleading. In the case of summer precipitation, and using the HADUKP version, the averages can vary depending on what period is used :-
MORAL – Be extremely of any claims about “normal” climate (especially when issued by the Met Office, or any other organisations run by ex WWF executives).