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

<p><span lang="en-US">The 2022 European drought </span><span lang="en-US">affected the whole of France, leading to very severe summer low-flows. </span><span lang="en-US">The </span><span lang="en-US">outstanding</span><span lang="en-US"> characteristics of this event </span><span lang="en-US">is questioned </span><span lang="en-US">within a long-term historical context. It first makes use of 600+ daily streamflow series gauging near-natural catchments </span><span lang="en-US">from</span><span lang="en-US"> all French regions. The historical background is provided by the </span><span lang="en-US">25-member ensemble hydrological reanalysis </span><span lang="en-US">FYRE Hydro which covers the period 1871-2012 for the above stations. </span><span lang="en-US">FYRE Hydro</span> <span lang="en-US">originates from </span><span lang="en-US">a 25-member </span><span lang="en-US">ensemble streamflow simulation </span><span lang="en-US">u</span><span lang="en-US">sing the GR6J lumped conceptual mode</span><span lang="en-US">l. 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 </span><span lang="en-US">(Devers et al., 2021) </span><span lang="en-US">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 </span><span lang="en-US">(Bourgin et al., 2014). An ensemble Kalman filter furthermore combined these ensemble simulations with available historical series </span><span lang="en-US">together </span><span lang="en-US">with their uncertainties to produce the FYRE hydro reanalysis. </span><span lang="en-US">Streamflow observations from 2022 are compared to </span><span lang="en-US">severe </span><span lang="en-US">drought years in the FYRE Hydro reanalysis as identified by Caillouet et al. (2021). </span><span lang="en-US">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.</span></p> <p>&#160;</p> <p>Bourgin, F., Ramos, M., Thirel, G., and Andr&#233;assian, V.: Investigating the interactions between data assimilation and post-processing in hydrological ensemble forecasting, Journal of Hydrology, 519, 2775 &#8211; 2784, 85 https://doi.org/https://doi.org/10.1016/j.jhydrol.2014.07.054, 2014</p> <p>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</p> <p>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&#8211;1879, https://doi.org/10.5194/cp-17-1857-2021, 2021</p>