Characterisation and interpretation of local climate evolution in the South-West of France

Summer 2022 has been the second hottest summer after 2003 in France since 1900, with 33 cumulative days of heatwaves. It has also been one of the 10 driest summers in France since 1959. The average precipitation deficit reached 20% compared to the 1991-2020 period, exceeding 60% in some regions, even though June 2022 broke the monthly record of storm occurrences.

These extreme climate conditions led to water restrictions and fostered the development of many wildfires. In particular, so called “megafires” burnt more than 28,000 hectares of the Landes forest in the Nouvelle-Aquitaine region, in the South-West of France.

Starting from the 18th century, this swampy region has been dried out by planting maritime pines and digging ditches to drain away excess water. Due to recent events, these land management practices are questioned : the record-breaking soil dryness of summer 2022 enabled fire to propagate underground and resurface further away, making firemen’s work extremely difficult.

By controlling ditch drainage, is it possible to reduce soil dryness and thus fire risk in summer, as well as mitigate heavy precipitation impacts in this flood prone area ? To answer this question, this work first aims at characterizing and interpreting local climate evolution during the last decades, in terms of trends, changes in the seasonal cycle and extreme events, using  ERA 5 reanalysis, the E-Obs dataset, and MODIS satellite observations. CORDEX regional climate projections are also analysed. Nouvelle-Aquitaine will experience both more frequent and intense heatwaves and droughts and an increase in heavy precipitations. Landes forest management thus has to be adapted.

The perspective of this work is to develop a conceptual ditch drainage model and quantify the drought and flood risk reduction potential using storylines based on plausible short and long term climate conditions in Nouvelle-Aquitaine.

In a broader perspective, the objective of this work is to develop a methodology replicable in other regions of the world to analyse the impacts of climate change at a local scale and explore how climate science can provide quantitative information to help decision making.