A study conducted in forested site of Ireland in the UK by researchers from Trinity College Dublin, NUI Galway and the UK’s Centre for Ecology and Hydrology in the UK has demonstrated that, whilst forested areas can play a part in reducing smaller storm flows, they are unlikely to help supress the impact of major flood events.
Forests play a vital role as carbon sinks areas of rich biodiversity and refuges for wildlife; however their value as potential mitigators of major floods may be less than has been previously supposed. The conclusions of the study were informed by data gathered from paired-catchment forestry studies which comprised 66 station-years of flow measurements within Ireland and the UK. In each case “coniferous evergreen trees were removed from one catchment with minimal soil disturbance while the adjoining control catchment was left unchanged. Trees were removed from 20% – 90% of the three experimental basins. Following woodland removal there was a large increase in dry weather baseflow at all sites. Baseflows increased by about 8% after tree removal from a quarter of the Hore basin and by 41% for the near-total cut at Howan. But the changes were more complex for peak flows. Tree harvesting increased the smallest and most frequent peak storm flows, indicating that afforestation would lead to the suppression of such events. This was however restricted to events well below the mean annual flood, indicating that the impact of forests upon the largest and most damaging floods is likely to be limited” as taken from the article’s abstract.
The study has widely implications for developers and land managers considering whether flood risk on prone sites could be mitigated through planting forest nearby.
The article is published within the journal Science of The Total Environment, as is available here: www.sciencedirect.com/science/article/abs/pii/S0048969721069539?via%3Dihub
Reference: L. Xiao, M. Robinson, M. O’Connor. Woodland’s role in natural flood management: Evidence from catchment studies in Britain and Ireland. Science of The Total Environment, 2021; 151877 DOI: 10.1016/j.scitotenv.2021.151877