Articles | Volume 20, issue 9
Hydrol. Earth Syst. Sci., 20, 3651–3672, 2016

Special issue: HYPER Droughts (HYdrological Precipitation – Evaporation...

Hydrol. Earth Syst. Sci., 20, 3651–3672, 2016

Research article 08 Sep 2016

Research article | 08 Sep 2016

Hierarchy of climate and hydrological uncertainties in transient low-flow projections

Jean-Philippe Vidal1, Benoît Hingray2,3, Claire Magand4,5, Eric Sauquet1, and Agnès Ducharne4 Jean-Philippe Vidal et al.
  • 1Irstea, UR HHLY, Hydrology-Hydraulics Research Unit, Villeurbanne, France
  • 2CNRS, LTHE UMR 5564, Grenoble, France
  • 3Université Grenoble Alpes, LTHE UMR 5564, Grenoble, France
  • 4Sorbonne Universités, UPMC, CNRS, EPHE, UMR 7619 METIS, Paris, France
  • 5IPSL, LSCE, UPMC, CNRS, UVSQ, Paris, France

Abstract. This paper proposes a methodology for estimating the transient probability distribution of yearly hydrological variables conditional to an ensemble of projections built from multiple general circulation models (GCMs), multiple statistical downscaling methods (SDMs), and multiple hydrological models (HMs). The methodology is based on the quasi-ergodic analysis of variance (QE-ANOVA) framework that allows quantifying the contributions of the different sources of total uncertainty, by critically taking account of large-scale internal variability stemming from the transient evolution of multiple GCM runs, and of small-scale internal variability derived from multiple realizations of stochastic SDMs. This framework thus allows deriving a hierarchy of climate and hydrological uncertainties, which depends on the time horizon considered. It was initially developed for long-term climate averages and is here extended jointly to (1) yearly anomalies and (2) low-flow variables. It is applied to better understand possible transient futures of both winter and summer low flows for two snow-influenced catchments in the southern French Alps. The analysis takes advantage of a very large data set of transient hydrological projections that combines in a comprehensive way 11 runs from four different GCMs, three SDMs with 10 stochastic realizations each, as well as six diverse HMs. The change signal is a decrease in yearly low flows of around −20  % in 2065, except for the more elevated catchment in winter where low flows barely decrease. This signal is largely masked by both large- and small-scale internal variability, even in 2065. The time of emergence of the change signal is however detected for low-flow averages over 30-year time slices starting as early as 2020. The most striking result is that a large part of the total uncertainty – and a higher one than that due to the GCMs – stems from the difference in HM responses. An analysis of the origin of this substantial divergence in HM responses for both catchments and in both seasons suggests that both evapotranspiration and snowpack components of HMs should be carefully checked for their robustness in a changed climate in order to provide reliable outputs for informing water resource adaptation strategies.

Short summary
Possible transient futures of winter and summer low flows for two snow-influenced catchments in the southern French Alps show a strong decrease signal. It is however largely masked by the year-to-year variability, which should be the main target for defining adaptation strategies. Responses of different hydrological models strongly diverge in the future, suggesting to carefully check the robustness of evapotranspiration and snowpack components under a changing climate.