Land-Atmosphere Interactions May Have Exacerbated the Drought and Heat Wave over Northern Europe during Summer 2018

The 2018 drought and heat wave over Europe was particularly exceptional over northern Europe, with unprecedented forest fires in Sweden, searing heat in Germany and water restrictions in England. Examination of ERA5 data verified with in situ soil moisture and surface flux measurements over Britain suggest the region entered a rare condition by the end of June of becoming a “hot spot” for land-atmosphere coupling. Land-atmosphere feedbacks were prompted by unusually low soil moisture over wide areas, which generated moisture limitations on surface heat fluxes, suppressing cloud formation, increasing surface net radiation and driving temperatures higher during several multi-week episodes of extreme heat. Monthly, daily and hourly data are examined to investigate the subseasonal-to-seasonal progression of the event and the diurnal evolution of tropospheric profiles in order to quantify the anomalous land surface contribution to heat and drought. Prediction skill for extreme events amplified by land-atmosphere interactions may depend on the ability of forecast models to replicate the transition to the sensitive feedback regime below a critical soil moisture value, which is examined in S2S and SubX ensemble forecasts for the period. Similar recent events over various parts of Europe in 2003, 2010 and 2019, combined with dire climate change projections, suggest such events are on the increase. Land-atmosphere feedbacks may play an increasingly important role exacerbating extremes and contributing to their predictability on S2S time scales over Europe.