Human-induced climate change directly influenced the winter 2013/2014 floods in southern England, reports a paper published online this week in Nature Climate Change. The study shows that the extreme rainfall that led to the floods was the result of two factors associated with global warming: an increase in the water-holding capacity of the atmosphere (thermodynamic changes) and more January days with westerly air flow (dynamic changes).
The succession of storms that reached southern England in the winter of 2013/2014 caused severe flooding that led to ￡451 million in insured losses. The possibility that anthropogenic climate change contributed to this event was much discussed at the time.
Nathalie Schaller, Neil Massey and colleagues used the ‘weather@home’ citizen-science project to model weather for January 2014 in both the current climate and one in which there was no human influence on the atmosphere. Looking at changes in precipitation (thermodynamic) and atmospheric circulation (dynamic), the authors estimate that anthropogenic climate change is responsible for a 43% increase in risk of the 1-in-100-year rainfall event seen in the winter of 2013/2014, with approximately 67% of the increased risk attributable to thermodynamic changes and 33% to dynamic changes. They use hydrological mapping of the Thames river catchment to show that, during the 2013/2014 floods, these changes in atmospheric circulation and precipitation caused higher peak 30-day river flow, and use flood risk mapping to show a small increase in flood risk for properties in the catchment.