Water vapour transport could prove to be a better predictive tool than rainfall for the forecasting of extreme flooding events according to a study published online in Nature Communications. The findings indicate that flood warnings could be extended by as much as three days in the UK and other parts of Europe.
Water vapour transport can refer to large areas of moisture that travel across the atmosphere in the form of giant atmospheric rivers. These rivers are associated with depressions as they wind their way across the North Atlantic Ocean towards Europe, where some of the water vapour within them will eventually fall as heavy rain. While forecasting heavy rainfall can be difficult, as it occurs on a day-to-day basis, atmospheric rivers operate on a longer timescale, which has led to the suggestion that water vapour transport could be a better predictive tool for flooding forecasts.
David Lavers and colleagues used the Ensemble Prediction System, from the European Centre for Medium-Range Weather Forecasts, to test this theory. The authors focus on the heavy rainfall and subsequent flooding that occurred during the wet winter of 2013/14 in an effort to evaluate the forecast potential of water vapour transport versus rainfall. They show that, in some European regions, including parts of England, Germany, and Spain, water vapour transport extends the forecast horizon by three days.
While a detailed study is needed to evaluate the false alarm rate of such a warning system, the use of water vapour transport, rather than rainfall, shows promise regarding increased warning and thus preparedness for extreme winter hydrological events in Europe.