As heavy rain continues to contribute to the devastating flooding in Cumbria, there have once again been calls – notably from the environmentalist George Monbiot – for the reforestation of our uplands, to help tackle rural flooding. The government has stated that it is funding the planting of 11m trees over the next five years to this end. It has also been suggested that trees could help reduce the number and severity of flash floods in cities, such as those that devastated Hull in June 2007.
To determine whether the humble tree really can provide such robust defences, we first need to understand the role they play in soaking up excess rain water. All floods, whether fluvial (when rivers burst their banks) or pluvial (when rainfall overwhelms drainage systems before it reaches rivers), are caused because the rain cannot soak into the soil fast enough. Instead, it runs rapidly over the surface of the land.
And while climate change is causing bigger and bigger storms, our alterations to the environment – especially to the ground surface – have been one of the major causes of the increased frequency of flooding events in modern times.