Atmospheric mercury (Hg) is deposited to land surfaces mainly through vegetation uptake. Foliage stomatal gas exchange plays an important role for net vegetation Hg uptake, because foliage assimilates Hg via the stomata. Here, we use empirical relationships of foliar Hg uptake by forest tree species to produce a spatially highly resolved (1 km2) map of foliar Hg fluxes to European forests over one growing season. The modelled forest foliar Hg uptake flux is 23 ± 12 Mg Hg season−1, which agrees with previous estimates from literature. We spatially compare forest Hg fluxes with modelled fluxes of the chemistry-transport model GEOS-Chem and find a good overall agreement. For European pine forests, stomatal Hg uptake was shown to be sensitive to prevailing conditions of relatively high ambient water vapor pressure deficit (VPD). We tested a stomatal uptake model for the total pine needle Hg uptake flux during four previous growing seasons (1994, 2003, 2015/2017, 2018) and two climate change scenarios (RCP 4.5 and RCP 8.5). The resulting modelled total European pine needle Hg uptake fluxes are in a range of 8.0 - 9.3 Mg Hg season−1 (min - max). The lowest pine forest needle Hg uptake flux to Europe (8 Mg Hg season−1) among all investigated growing seasons is associated with unusually hot and dry ambient conditions in the European summer 2018, highlighting the sensitivity of the investigated flux to prolonged high VPD. We conclude, that stomatal modelling is particularly useful to investigate changes in Hg deposition in the context of extreme climate events.

Despite rapid progress in the burgeoning field of flash drought research, few studies directly compare the differences in characteristics between flash drought (commonly understood as quick, rapid-onset drought) and drought traditionally defined as slow-moving (henceforth normal drought), particularly over agricultural regions where drought effects may be economically the most disastrous. In this study, flash and normal drought events are identified using reanalysis soil moisture in the data-rich agricultural region of the California Central Valley for investigation of characteristics related to agriculture. In particular, we investigate the relative duration of pixels in drought events, the correlation of drought intensity with vegetation condition, the impact of aridity on vegetation response and drought, and the differences in the different characteristics between rainfed and irrigated agriculture. Overall, we found considerable differences between flash and normal drought, particularly in their spatial distributions and behavior in relation to aridity. Flash droughts even indicate a counterintuitive improvement in vegetation condition in the northern, more humid regions, likely due to the release of growth limiting factors (e.g. below-optimum temperature and radiation) associated with drought. Results also indicate improvements in vegetation conditions during normal drought for irrigated land over rainfed, highlighting the importance of irrigation as a drought protection strategy in agriculture.