Assessing the effects of heat and droughts on forest-climate interactions in Europe using a regional climate model with an interactively coupled vegetation module

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Forests play a pivotal role in the climate system by exchanging energy, water, and gases with the atmosphere. Through biogeochemical processes such as photosynthesis, respiration, and transpiration, forests heavily influence the carbon and water cycles. In particular, their capacity to sequester carbon through photosynthesis demonstrates their role as carbon sinks. Further, through biogeophysical processes forests influence the local and regional climate by determining local temperature and humidity distributions. However, forests not only influence the climate - they are also affected by it. Their vulnerability to climate extremes, particularly to heat and droughts, raises substantial challenges. Droughts induce water stress, affecting both biogeochemical and biogeophysical processes, at the soil-forest-atmosphere interface. Within the EU Horizon project OptFor-EU and in collaboration with the Euro-CORDEX Flagship Pilot Study LUCAS, we employ numerical models to assess the climate-forest interactions and to evaluate forest resilience in a changing climate. In this study, we examine the effects of heat and droughts on European forests and their climatic feedbacks in simulations using the regional climate model REMO2020 coupled with its interactive, mosaic-based vegetation module iMOVE. The coupling enables the exchange of crucial parameters on model timestep level, and therefore, captures the complex interactions between climate, soil, and vegetation. We focus on biophysiological forest parameters such as the leaf area index (LAI), as well as on biophysical processes such as evapotranspiration, and on their feedbacks with the regional climate. Our simulations cover the European continent and have a horizontal resolution of 0.11°, forced with reanalysis data from ERA5.1 at the lateral boundaries. Starting from 1981 until 2020, they cover the hot and dry years of the last decades, such as 2003 and 2018-2020. Our findings reveal insights into the vulnerability and resilience of European forests to heat and drought events, as well as into their role in climate extremes mitigation.

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