The outstanding 2022 hydrological drought in France within a 150-year historical context

The 2022 European drought affected the whole of France, leading to very severe summer low-flows. The outstanding characteristics of this event is questioned within a long-term historical context. It first makes use of 600+ daily streamflow series gauging near-natural catchments from all French regions. The historical background is provided by the 25-member ensemble hydrological reanalysis FYRE Hydro which covers the period 1871-2012 for the above stations. FYRE Hydro originates from a 25-member ensemble streamflow simulation using the GR6J lumped conceptual model. These simulations integrate three types of uncertainty: (1) the meteorological uncertainty through the use of the 25 members of the high-resolution FYRE Climate meteorological reanalysis (Devers et al., 2021) as forcings, (2) the uncertainty in streamflow measurement used to calibrate the hydrological models, and (3) the hydrological model error based on relative discrepancies between observed and simulated streamflow (Bourgin et al., 2014). An ensemble Kalman filter furthermore combined these ensemble simulations with available historical series together with their uncertainties to produce the FYRE hydro reanalysis. Streamflow observations from 2022 are compared to severe drought years in the FYRE Hydro reanalysis as identified by Caillouet et al. (2021). Results show that 150-year records were broken over a large number of stations for various low-flow indicators, confirming the exceptional nature of this hydrological drought event.

 

Bourgin, F., Ramos, M., Thirel, G., and Andréassian, V.: Investigating the interactions between data assimilation and post-processing in hydrological ensemble forecasting, Journal of Hydrology, 519, 2775 – 2784, 85 https://doi.org/https://doi.org/10.1016/j.jhydrol.2014.07.054, 2014

Caillouet, L., Vidal, J.-P., Sauquet, E., Devers, A., Lauvernet, C., Graff, B., and Vannier, O.: Inter-comparison of extreme low-flow events in France since 1871, LHB: Hydroscience Journal, 107, 1-9 https://doi.org/10.1080/00186368.2021.1914463, 2021

Devers, A., Vidal, J.-P., Lauvernet, C., and Vannier, O.: FYRE Climate: a high-resolution reanalysis of daily precipitation and temperature in France from 1871 to 2012, Clim. Past, 17, 1857–1879, https://doi.org/10.5194/cp-17-1857-2021, 2021