Impact of Surface Roughness Changes on Surface Wind Speed Over Western Europe: A Study With the Regional Climate Model RACMO

The temporal trend of wind speed near the surface over land has been investigated over recent decades. A prevailing trend of decline was found in several studies for most areas in the Northern hemisphere, denoted as terrestrial stilling, with multiple causes being discussed. In this study, we focus on the impact of changes of surface roughness due to changes in land‐use and vegetation cover on this variable for western Europe using the regional climate model RACMO driven by ERA5 reanalysis. We conduct two simulations at climate scale, with and without changes in land‐use and vegetation on a yearly basis. We find that upper level large‐scale circulation slowing down results in declining near surface mean wind speed, and that increases in surface roughness due to changes in land use and vegetation cover play an important role in intensifying this declining trend from our simulations with RACMO. However, the trends inferred from the model simulations and ERA5 are not consistent with trends derived from gridded observations database E‐OBS. This could come from the complexity of integrating in‐situ measurements with uncorrectable inhomogeneity to derive E‐OBS. Plain Language Summary Wind speed near the surface (10 m above ground) has been declining over many areas in the Northern hemisphere, denoted as terrestrial stilling. This declining trend can be affected by different factors such as increase in surface roughness due to land‐use and vegetation cover changes, large‐scale circulation changes, anthropogenic aerosols and climate change due to greenhouse gas concentration increase. In this study, we focus on the impact of changes in land‐use and vegetation cover on this variable for western Europe using a regional climate model RACMO. We simulate wind speed using two model setups, with and without changes in land‐use and vegetation on a yearly basis. We find that a slowing down of the upper level large‐scale circulation results in a decline of the near‐surface mean wind speed. In addition, we find that based on the difference between our two simulations with RACMO, increases in surface roughness due to changes in land use and vegetation cover intensify this declining trend in near‐surface mean wind speed. Key Points Wind speed has been decreasing over a large part of western Europe from the surface to 500 hPa according to ERA5 reanalysis Regional climate model simulations forced by ERA5 can reproduce those large‐scale features of wind speed well The increase in