Droughts such as experienced in the summer of 2003 could have a durable impact on terrestrial ecosystems

Based on the analysis of the extreme heat wave and drought in Europe during the summer of 2003, CEA-CNRS and INRA researchers have studied the impact of climatic change on terrestrial ecosystems. These results were obtained using a unique monitoring network measuring carbon and water fluxes in a representative set of forests and prairies in Europe, and with an atmospheric modelling system.

The scientific community generally considers that global warming in the 21st century will lead to an increase in vegetable productivity in Europe and temperate latitudes, among other reasons due to carbon sequestration by vegetation and the extension of the growth period during the spring. The results obtained by researchers show that, on the contrary, strong droughts such as those experienced in 2003 have a negative effect on biomass production and ecosystem functioning.

Looking at the year 2003 within the context of the climatic changes since the last century, researchers have observed that the heat and drought have caused an unprecedented decrease of 30% in vegetable activity throughout the European continent, leading to an abnormal discharge of CO2 into the atmosphere. The extreme temperatures and especially the exceptional deficit in precipitation accelerated the drying of soils and produced altered photosynthesis, with effects that lasted until the fall. Instead of increasing with the increase in temperature, the respiration of ecosystems has decreased along with the decrease in vegetable production.

The researchers feel that it is still too soon to assess the long-term damage to vegetation (resistance to pathogens, dying of trees, changes in vegetation, impact on agriculture, etc.). With simulations of future climatic changes predicting that such events will become more frequent over the century, these results raise important questions on the capacity of our ecosystems to withstand climatic changes and on the measures to be taken to facilitate this adaptation.