The role of forests in managing future floods and droughts
Climate change will increase the risk of floods and droughts in most regions of the world, with potentially very significant impacts on the welfare of people. While the impacts will be felt most keenly in the poorest countries, Europe and North America will not be spared. Selectively increasing forest coverage will play a critical role in helping us to adapt to these changes and in mitigating their impact, in addition to sequestering carbon and improving biodiversity.
In the UK, the Global Futures initiative estimates suggest that climate change could increase the frequency of extreme flooding events by two to three times by the 2050s, potentially affecting up to 2.5 million properties, with economic damages of up to £12 billion [i]. Additionally, up to 50% of summers by the 2080s could see drought conditions comparable to or more severe than the 1976 drought, potentially impacting water supplies for almost the whole population.
Why forests are critical to regulate flood risks
Forests play a critical role in reducing flood risk by promoting evaporation, improving soil structure, decreasing soil erosion, and exerting a drag on floodwaters, which delays flood flows. Also, trees absorb and store water during dry periods, reducing the risk of drought and ensuring a more consistent supply of water for agriculture and human consumption. Trees can also help regulate temperature, reducing the risk of heatwaves and other extreme weather events exacerbated by climate change.
Regional climate, geology, soil type, and soil condition all influence tree water use and the effectiveness of tree planting in reducing flood risk. For example, planting in the wetter and windier uplands of the UK will maximize the contribution of storm-day, canopy interception loss to reducing flood flows, while woodland creation in the warmer and drier lowlands will potentially contribute more below-ground floodwater storage due to greater soil drying and higher soil moisture deficits. However, this can exacerbate low flows in dry periods and pose an issue for water supplies and the wider freshwater environment, so it's important to consider downstream waters and wetlands that are sensitive to a reduction in water quantity.
Maximising the effectiveness of tree planting
The precise location of planting within a flood risk catchment also influences its ability to affect flood run-off pathways, and it's helpful to target planting directly along or across run-off pathways, for example in the form of cross-slope shelterbelts or within riparian zones and on floodplains, where the drag or roughness effect of woodland will be greatest. Tree planting can also increase the effectiveness of specific features designed to slow run-off, such as swales, infiltration basins, and sustainable drainage systems. A related benefit of slowing flood flows is to potentially increase groundwater recharge, which can enhance low flows and help to offset the impact of the higher tree water use on these.
Source: Designing and Managing forests and woodlands to reduce flood risk Oct 2022 [iii]
Overall, planting new forests is a valuable investment in the long-term health and resilience of our natural systems, and a critical step towards ensuring a sustainable future for generations to come. Creating new woodland is a key component of the UK’s flood defence strategy[i].
Landowners considering planting new forests should carefully consider the regional climate, geology, soil type, and soil condition, as well as the precise location of planting within a flood risk catchment, to maximise the effectiveness of tree planting in reducing flood risk and adapting to climate change.
To obtain a tailored assessment on your landholding or cluster optimised for your regional climate, geology, soil type and condition - contact us: hello@zuluecosystems.com
[i] [https://www.edie.net/flooding-and-coastal-damages-risking-12bn-to-uk-economy/]
[ii] [https://www.gov.uk/government/publications/national-flood-and-coastal-erosion-risk-management-strategy-for-england--2]
[iii] [Woodland nature flood defence: https://docsend.com/view/6453k68v9k3xx8ak]