How do land-use changes shape the occurrence of extreme temperatures across Europe?

In recent years, an increase in the frequency of occurrence of heatwaves and in the number of hot days in Europe is undeniable. Hence, there is an increased need to understand the feedback mechanisms relevant to their development. Due to their localised impact and although they modify local land surface properties that control the land-atmosphere mass, energy, and momentum exchanges, the influence of land use/land cover changes (LUC) at regional scales still needs to be better represented in coordinated downscaling experiments. The Flagship Pilot Study LUCAS (Land Use & Climate Across Scales) provides a coordinated effort to study LUC using an ensemble of 11 regional climate models (RCMs). In the first phase of the project, three experiments were performed for continental Europe: eval (current climate), grass (trees replaced by grassland), and forest (grasses and shrubs replaced by trees). Heat events can be defined using percentiles, and heat waves are periods of consecutive hot days where temperatures exceed a certain percentile. Here, we use P85, P90 and P95 for maximum temperature thresholds and consider durations of 5, 7, and 10 days.  To facilitate the comparison of the intensity of these extreme events and their evolution over time, we normalise the daily maximum temperature, latent heat and soil moisture using a seasonal interquartile range. An analysis of frequency, magnitude, duration and extension is performed for the three percentiles and for the different land covers.

The results suggest that model responses to afforestation and deforestation exhibit some variability, particularly during summer months. While a substantial proportion of the models indicate a potential enhancement in the intensity and magnitude of heat extremes under forest scenarios, others demonstrate more muted or contrasting effects. The objective of the present analysis is to understand these discrepancies among models and their implications for land-atmosphere interactions under various land use scenarios. The findings will be discussed in terms of their relevance to climate extremes, providing insights into the role of LUC in modulating heat events across Europe.