Northern Europe is not a place we think of as experiencing water limitation. In this normally damp and cloudy region, increases in air temperature or sunlight are correlated with higher evapotranspiration rates and increased humidity surface humidity. During the anomalously dry summer of 2018, however, Dirmeyer et al.  show that soil moisture in Great Britain and large parts of Northern Europe dropped below a threshold where increasing air temperatures no longer correlated with surface humidity. Instead, these regions switched a water limited regime, where evapotranspiration could not cool the surface as efficiently. This further exacerbated extreme hot and dry conditions, a net positive feedback.
In the accompanying viewpoint, Orth  highlights the importance of identifying such thresholds in coupling energy and water balance between soils, plants and the atmosphere, and how improved models can help predict the course of future, increasingly common, weather extremes.
Citation: Dirmeyer, P., Balsamo, G., Blyth, E., Morrison, R. & Cooper, H. . Land-Atmosphere Interactions Exacerbated the Drought and Heatwave over Northern Europe during Summer 2018. AGU Advances, 2, e2020AV000283. https://doi.org/10.1029/2020AV000283
—Susan Trumbore, Editor-in-Chief, AGU Advances