High resolution regional climate model points to a wetter UK with widespread afforestation

Interest continues to grow in the benefit of afforestation for carbon sequestration, yet the potential consequences of largescale afforestation on terrestrial hydrology are still unknown. Furthermore, it is unclear how large land cover changes may alter the surface-atmosphere hydrological connection, particularly as the climate and hydrological cycle evolve. In this study, we investigate how terrestrial and atmospheric hydrological processes in the UK may alter with increases in woodland across the UK, Ireland, and parts of Western Europe. We use a convection permitting physics-based regional climate model (HadREM3-RA11M) at 2.2 km resolution to simulate and identify the responses of afforestation on hydrology. Afforestation scenarios were generated using existing datasets from regional authorities and previous studies, with tree type determined according to pre-existing landcover. We compare modelled scenarios of widespread afforestation and existing land cover for a future period up to 2080 (with Representative Concentration Pathway 8.5) to assess the consequences of expanded woodland on terrestrial and atmospheric processes within the UK in a much warmer climate.

 

Model results show clear and substantial changes in hydrology in both the atmosphere and land surface with woodland expansion. Soil moisture increases, leading to a commensurate boost to subsurface flows, which is particularly greater in summer months. Although runoff increases throughout the country, there is a proportionally greater increase in the drier south-eastern UK. Evaporation broadly decreases across the country, primarily driven by a reduction in soil evaporation, although this varies seasonally. Precipitation patterns also alter substantially, with increases in the west and slight increases and decreases in the east of the country. These results provide unique insights into how models that couple the land surface with the atmosphere can identify potentially far-reaching consequences of afforestation in temperate regions.