Forests can help prevent floods and droughts

One third of European territory is covered by forests (mostly managed) and approximately 296 million Europeans live in or close to forests. Forests are essential for human well-being and provide a wide range of ecosystem services to society, including ‘water retention’, defined as the water absorbed or used by forests.

The EEA report ‘Water-retention potential of Europe's forests’ shows that water retention has an important role to play in buffering the effects of heavy rainfall and droughts. A better understanding of this role can help develop measures to tackle the effects of climate change and extreme weather events.

The volume of water retained by forests can depend on characteristics such as forest cover area, the length of vegetation growing season, tree composition and tree density, as well as the age and the number of layers of vegetation cover. Water retention by forests affects the amount and timing of the water delivered to streams and groundwater by increasing and maintaining infiltration and storage capacity of the soil. Forests can soak up excess rainwater, preventing run-offs and damage from flooding. By releasing water in the dry season, forests can also help provide clean water and mitigate the effects of droughts.

The report shows that water retention potential tends to increase along with the extent of forest cover in a water basin. Compared to basins with a forest cover of 10%, total water retention is 25% and 50% higher in water basins where the forest cover is more than 30% and 70%, respectively.

Irrespective of the extent of the basin’s forest cover, water retention is typically about 25% greater in summer time than in winter time and that coniferous forests in general retain 10% more water than broadleaved forests or mixed forests. In general, forests in Alpine and Continental regions have the highest water-retention potentials, while Atlantic and Mediterranean regions register lower water-retention potentials.

The report suggests that despite its important role, water retention by forests cannot be promoted as a one-size-fits-all solution. Instead, water retention should be considered on a case-by-case basis according to local and regional ecological and hydrological conditions, as proposed in the natural water-retention measures catalogue of the European Commission .