Hot days are expected to become more frequent with climate change. Heat extremes can be exacerbated by dry conditions due to a lack of evaporative cooling. This has been shown to be an important mechanism for future amplification of heat extremes in several regions. However, it remains unclear how well global climate models can simulate these interactions between hot and dry conditions under current climate conditions.

We therefore evaluated the climate models against flux tower data, the best available observations of evapotranspiration. We showed that many models overestimate the interaction between hot and dry conditions in wet regions and consequently overamplify heat extremes. Our study points to an area of necessary model improvement to increase confidence in future projections of heat extremes.