Spatial variability and future evolution of surface solar radiation over Northern France and Benelux: a regional climate model approach

Abstract. Improving knowledge of current and future spatio-temporal variability of surface solar radiation is essential in the context of climate change and associated environmental and societal issues. Such an evolution will be influenced by changes in both meteorological parameters and atmospheric composition, notably by anthropogenic emissions. We investigate both all-sky and clear-sky surface solar radiation (SSR) variability, along with cloud cover, aerosols and water vapor content, over Northern France and Benelux. This region of Europe is largely influenced by cloudy conditions and anthropogenic aerosols, especially nitrate species. Our analysis relies on the CNRM-ALADIN64 regional climate model at 12.5 km x 12.5 km spatial resolution, which includes the TACTIC interactive aerosol scheme. First, hindcast reanalysis-driven simulations over 2010–2020 allow a regional evaluation of ALADIN outputs and to investigate recent spatial variability of SSR and associated atmospheric parameters. Secondly, their possible evolution at mid and end of the 21st century are investigated based on ALADIN climate simulations following two contrasted CMIP6 scenarios, namely the shared socioeconomic pathways (SSP), SSP1-1.9 and SSP3-7.0. Our regional evaluation of clear-sky and all-sky SSR, clear-sky frequency and aerosols over northern France and Benelux shows reasonable agreement between 2010–2020 ALADIN hindcast simulations and coincident multi-site ground-based measurements, despite some overestimation of nitrate aerosols in spring and an overall underestimation of organic particles by the model. Focusing on spring and summer seasons, hindcast simulations show maximum of solar radiation around the southern parts and over sea areas of the region. In addition to latitudinal effects, elevated aerosol loads over Benelux, and high cloud cover over the South West of England reduce the SSR. Compared to 2005–2014 atmospheric conditions, ALADIN mid and long-term simulations for SSP1-1.9 predict a significant reduction of aerosol loads, especially over the Benelux, associated with an increase in future clear-sky SSR but geographically limited all-sky SSR evolution. In contrast, SSP3-7.0 simulations projected pronounced and extended decreases of clear-sky and all-sky SSR over most of the Benelux/northern France region. These reductions are maximum in spring due to combined effects of cloud cover and nitrate aerosol increases over the Benelux starting in 2050, that are amplified by an additional water vapor increase in 2100. Thus, this regional climate model approach suggests that future SSR evolution over this part of western Europe will be drastically affected by combined effects of anthropogenic aerosol emissions trajectories, cloud cover and water vapor changes, which also induce strong spatial patterns.