Impact of climate change on streamflow in France: Towards new river flow regimes?

A large transient multi-scenario and multi-model ensemble of future streamflows and groundwater projections in France developed in a national project named Explore2 was recently published (Sauquet et al., 2024). The main objective of the Explore2 dataset is to provide a rich and spatially consistent information for the future evolution of hydrological resources in France using a large ensemble of EURO-CORDEX regional climate projections (Coppola et al., 2021) and a large variety of hydrological models.

The aim of the present study is to use a classification of river flow regimes on the hydrological projections from the Explore2 dataset to assess how hydrological processes will change in response to climate change at the catchment scale.

A simple, but well-adapted classification based on a hierarchical cluster analysis is adopted here. The classification is based on the twelve monthly Pardé coefficients derived from 611 time series of near natural observed streamflow, leading to seven characteristic river flow regimes in France over the period 1976-2005.

The Pardé coefficients were computed on 30-year periods for four time slices, namely the baseline (1976-2005), near future (2020-2049), mid-century (2041-2070), and end of the century (2070-2099) periods for each hydrological projection and for 2500 simulation points located across France. A representative regime is assigned to each simulation point corresponding to the most frequent regime identified among all hydrological projections.

River flow regime derived from the historical runs is used to assess the performance of the hydrological models at each gauged basins. The shifts in river flow regimes (between the future and baseline periods) reflect and summarize the evolution in rainfall-runoff processes due to climate change.

Overall, the predominantly rain-fed hydrological regimes will change for more contrasted regime during the 21st century. The basins with transition regimes (combining snow and rain contributions) will likely shift towards pluvial regimes. Basins at higher altitudes will keep their nival character but will have less contrasted regimes, with potentially less severe low flow in winter, and a decrease in summer flow for rivers influenced by glaciers.

References:

Coppola et al.: Assessment of the European Climate Projections as Simulated by the Large EURO-CORDEX Regional and Global Climate Model Ensemble, J. Geophys. Res.: Atmos., 126, e2019JD032356. https://doi.org/10.1029/2019JD032356, 2021.

Sauquet et al.: A large transient multi-scenario multi-model ensemble of future streamflows and groundwater projections in France, ESSD, submitted.

Strohmenger et al.: On the visual detection of non-natural records in streamflow time series: challenges and impacts, Hydrol. Earth Syst. Sci., 27, 3375–3391, https://doi.org/10.5194/hess-27-3375-2023, 2023.