In principle, there is a fundamental link between climate change and flooding because, put simply, a warmer atmosphere holds more moisture.
Correspondingly, climate change projections suggest future increases in flood severity are likely for the UK. But are we seeing an impact of climate change in the increased flood trends we have witnessed over recent decades?
Moving from trend detection through to attribution is challenging due to pronounced variability between years and between decades – as can clearly be seen by the “wobbles” in the smoothed red lines on the time series charts above. This “noise” makes it hard to detect any “signal” associated with warming.
Moreover, it is worth addressing what causes these wobbles. At the latitude of the UK, a warming atmosphere generally means more rainfall, but in any one location the effect of a changing climate is complicated by changes to weather patterns. Atmospheric and oceanic circulation patterns vary naturally on a range of timescales, between years and decades – and this is what drives variability in river flows over time.
The UK sits on the edge of the Atlantic Ocean, so this is particularly important. For example, the increases in flooding over the past five decades in northern and western Britain have been associated with changes in the North Atlantic Oscillation (NAO), which affects the position of storm tracks across the UK and has a strong influence on rainfall. In collaboration with an international team, we have highlighted the role of variability in Atlantic sea-surface temperatures (the Atlantic Multidecadal Oscillation, AMO) on European floods.