Stormwater attenuation systems such as ours are going to have a greater role in the future, according to what the Met Office is saying.
The frequency of extreme rainfall in the UK may be increasing, according to Met Office analysis, as statistics show that days of particularly heavy rainfall have become more common since 1960. The analysis is still preliminary, but the apparent trend mirrors increases in extreme rain seen in other parts of the world. The study into extreme rain is based on statistics from the National Climate Information Centre, the UK’s official climate record.
Extreme rain is defined as the sort of downpour you would expect once in 100 days. Last year, for instance, extreme rain fell around once every 70 days.
Such weather helped make 2012 the wettest year in the UK in recorded history. There are big swings in rainfall from year to year, but the overall trend is upwards since 1960. The phenomenon of more frequent downpours has already been noted elsewhere, particularly in China and India.
There’s evidence to say we are getting slightly more rain in total, but more importantly it may be falling in more intense bursts – extreme stormwater conditions.
Scientists say that as the world has warmed by 0.7C, the atmosphere is able to hold 4% more moisture, which means more potential rain. The change in the UK trend is slight, but if the trend is confirmed it will clearly increase the risk of flooding.
A series of downpours in late November brought one of the wettest weeks in the last 50 years, causing major disruption.
Professor Julia Slingo, chief scientist at the Met Office, said the preliminary analysis needed further research but was potentially significant.
“We have always seen a great deal of variability in UK extreme rainfall because our weather patterns are constantly changing, but this analysis suggests we are seeing a shift in our rainfall behaviour,” she said. “There’s evidence to say we are getting slightly more rain in total, but more importantly it may be falling in more intense bursts – which can increase the risk of flooding.
“It’s essential we look at how this may impact our rainfall patterns going forward over the next decade and beyond, so we can advise on the frequency of extreme weather in the future and the potential for more surface and river flooding.
“This will help inform decision-making about the need for future resilience both here in the UK and globally.”
The Met Office no longer publishes a seasonal forecast and will not speculate on whether 2013 will produce frequent extreme rain.