<p>The trends of meteorological parameters and surface downward shortwave and longwave radiation (DSR, DLR) were analyzed at four stations (between 370 and 3580 m asl) in Switzerland for the 1996–2015 period. Ground temperature, specific humidity and atmospheric integrated water vapor (IWV) increased during all-sky and cloud-free conditions. All-sky DSR and DLR trends were in the ranges 0.6–4.3 W m<sup>−2</sup>/decade and 0.9–4.3 W m<sup>−2</sup>/decade, respectively, while corresponding cloud-free trends were −2.9–3.3 W m<sup>−2</sup>/decade and 2.9–5.4 W m<sup>−2</sup>/decade. The cloud radiative effect (CRE) was determined using radiative transfer calculations for cloud-free DSR and an empirical scheme for cloud-free DLR. CRE decreased in magnitude by 0.9–3.1 W m<sup>−2</sup>/decade which implies a reduction in cloud cover and/or a change towards a different cloud type over the four Swiss sites. Between 10 and 70 % of the increase in DLR is explained by factors other than ground temperature and IWV. Trends in aerosol optical depth at each station over the same period remained insignificant, and thus their contribution to the observed changes in surface radiative fluxes was negligible. A more detailed, long-term quantification of cloud changes is crucial and will be possible in the future as cloud cameras have been measuring at three of the four stations since 2013.</p>