The importance of water retention (the rainfall absorbed or used within an ecosystem) for mitigating flood and drought conditions and contributing to clean drinking water, for example, has been increasingly recognized in Europe in the past decade. Along with wetland preservation, better agriculture practices and other measures, preserving and re-growing forests are seen as key to enhanced natural water retention. Forests cover a third of Europe, and:
can soak up excess rainwater, preventing run-offs and damage from flooding. By releasing water in the dry season, forests can help to provide clean water and mitigate the effects of droughts [EEA 2015: 6].
In recognition of the important water management role of forests and other natural ecosystems, new policy instruments have proposed Natural Water-Retention Measures (NWRMs).
Natural Water-Retention Measures (NWRMs) are defined as ‘measures to protect and manage water resources and to address water-related challenges by restoring or maintaining ecosystems, natural features and characteristics of water bodies using natural means and processes’ (European Commission and Directorate-General for the Environment 2014). … The main focus is to enhance and preserve the water retention capacity of aquifers, soil and ecosystems and improve their status [EEA 2015: 9].
This EEA study found that:
In water-basins where the forest cover is 30%, water retention is 25% higher than in basins where the forest cover is only 10%. In basins where the forest cover is 70%, water retention is 50% higher than in basins where the forest cover is only 10%. … Coniferous forests in general retain 10% more water than broadleaved forests or mixed forests [EEA 2015: 5].
European Environment Agency, 2015, Water-retention potential of Europe's forests: A European overview to support natural water-retention measures, EEA Technical Report, No. 13/2015, https://www.eea.europa.eu/publications/water-retention-potential-of-forests