Land use and natural flood management

Heavy rainfall across the north of England has caused widespread flooding over the past two weeks, with thousands of households affected. The number of floods is projected to increase in Britain as the climate warms, but many other factors affect flood risk: today I want to discuss land use.

This animation of land use change in Europe since 1900 clearly shows how the settled areas and cropland in the UK have increased over the past century. Interestingly, the forest cover has actually increased during this time (especially visible in Scotland): from a low of just 5.0% in 1919, to 12.9% today. Source: Wageningen University

Land use change including deforestation, wetlands drainage, and construction on floodplains all contribute to a situation where 1 in 6 houses in the UK is now at risk of flooding. Increasingly, natural flood management techniques are being used to try and mitigate flooding in the UK by restoring degraded ecosystems.

I like this infographic summarising key natural flood management approaches beind undertaken in Scotland. Source: SEPA

Reforestation

Despite ambitious planting targets, there is still doubt as to whether the amount of forest cover is actually increasing in Britain. Reforestation of large areas of an upper catchment can reduce the peak flood height by up to 20%, while floodplain woodlands can also reduce erosion and improve water quality.

Wetlands restoration

Wetlands act as storage for excess water, regulating the rate of runoff. Restoring upland peat bogs slow water in the upper catchments of many flood-prone areas; a programme of tree-planting, wetland restoration, and the wonderfully-named leaky dams is credited with protecting the town of Pickering in Yorkshire from floods in 2015.

Agriculture

Some agricultural practices can increase flood risk, from compacting soil and ploughing down hills which increases runoff, to the clearance of protective ecosystems. The role of farmers in land management can be highly controversial: are moorlands denuded and lifeless as a result of clearances for grazing and game shooting, or is the ecosystem maintained primarily by the work of farmers?

Peat bogs on moorland are restored by building dams and closing gullies. This allows more water to be stored in the peat, regulating the speed of release into lower catchments and reducing the risk of floods, but defintitely increasing the percentage of hikers who end their day with wet feet :( Photo: Moors for the Future

While there's still work to be done regarding the engagement of the agricultural sector in NFM, long-term planning and careful engagement with stakeholders can ensure that ecosystems are managed in a way which benefits as many as possible (including beavers) while also reducing flood risk.

It's encouraging that the government is increasingly funding NFM, but it needs to be undertaken as part of an integrated approach, rather than on an ad hoc basis. This means addressing the elephant in the room: construction on floodplains.

Paving over permeable surfaces, thus reducing the ground absorption capcity and increasing runoff is well known as a driver of flood risk, but with an ongoing housing crisis and thousands of new homes are planned for construction in flood risk areas, there's limited political will to regulate construction more closely. Instead, more money is put into protecting high-value property, meaning wealthier areas can get more protection than poor ones, with consequences I've already discussed.

Activist group Extinction Rebellion floated a house down the River Thames earlier this month to draw attention to increased flood risk due to climate change. Photo: Guy Reece

The choices surrounding flood risk management are inevitably political, but that shouldn't mean that it isn't possible to have honest public conversations about the trade-offs required by different approaches. So far, it doesn't seem to be happening.

ETA - the America Adapts podcast gets into NFM in a big way over three episodes, and it's fascinating stuff.