Climate change caused by humans has made the likelihood of extreme rainfall similar to that seen in England this winter significantly higher, according to analysis seen by the Guardian.

Rainfall events that would previously have occurred only once in a century are now likely to be witnessed once every eighty years in the south of England, the Oxford University work shows.

That will mean far more frequent severe floods for residents of the crowded region, with what were once extremely rare events now happening much more often than the infrastructure of the region is equipped for. The research shows an increase in the rate of such events of about 20 to 25%, which significantly alters the number of homes likely to be vulnerable to flooding.

Friederike Otto, from the university’s school of geography and the environment, said: “It will never be possible to say that any specific flood was caused by human-induced climate change. We have shown, however, that the odds of getting an extremely wet winter [in the UK] are changing due to man-made climate change. Past greenhouse gas emissions and other forms of pollution have loaded the weather dice so the probability of the south of England experiencing extremely wet winters has increased.”

The scientists who conducted the study warned that this estimate of the frequency of extreme rainfall was based solely on current levels of observed rainfall in the recent past, compared with historical levels and those predicted for the future under a wide variety of possible scenarios under climate change.

This method means that if global warming leads, as expected in the future, to higher rainfall in already wet areas of the globe, including the UK, then this frequency could rise much further still. If that were the case, many more thousands of homes in the UK could be vulnerable to flooding, or to worse extremes of weather.

The analysis was arrived at by one of the most significant examples to date of scientists using the power of home computers to crunch vast amounts of data. The weather@home project drew on the power of more than 60,000 volunteers who allowed their personal computers to be used to process raw data gathered from observations of weather patterns.

Specialised software allowed the computers to be used to safely to process the figures, and return them to the scientists, from which the climate change experts were able to deduce key findings such as the increased likelihood of extreme weather events in the south of England.



Under the programmes, the scientists used the spare capacity on home computers to compare tens of thousands of simulations of possible weather in our present-day climate with tens of thousands of simulations of a hypothetical world without the influence of past greenhouse gas emissions in the atmosphere, using the same climate model.

However, the scientists now want to refine the data still further, to include elements reflecting the UK’s individual geography and hydrology –such as river locations, underlying rock formations, lowlying flood plains, and the flow of water from upland areas to lowlands.

That should enable a much more detailed picture to be drawn up of the likelihood of floods across the region. At present, the scientists are only able to say that high levels of rainfall are much more likely than in the past, whereas with a greater refinement they may be able to say with precision how much more likely flooding events are in particular localities.