The Fate of Stationary Tools for Environmental Flow Determination in a Context of Climate Change

Abstract

Environmental flows (eflows) refer to the amount of water required to sustain aquatic ecosystems. In its formal definition, three flow characteristics need to be minimally maintained: quantity, timing and quality. This overview paper highlights the challenges of some of the current methods used for eflow determination in the context of an evolving climate. As hydrological methods remain popular, they are first analyzed by describing some of the potential caveats associated with their usage when flow time series are non-stationarity. The timing of low-flow events will likely change within a season but will also likely shift in seasonality in some regions. Flow quality is a multi-faceted concept. It is proposed that a first simple step to partly incorporate flow quality in future analyses is to include the water temperature as a covariate. Finally, holistic approaches are also critically revisited, and simple modifications to the Ecological Limits of Flow Alteration (ELOHA) framework are proposed.

Environmental flow assessment in the context of climate change: a case study in Southern Quebec (Canada)

“…Despite this caution, these three hypotheses, mainly the stationarity, were not validated for the 284 sites considered in this study, which explains the varying sample size described in Table 2. St-Hilaire et al (2021) reiterated the fact that environmental flow assessment usually required stationary condition to fit statistical distribution with constant parameter values to the empirical distribution of extremes. When this is done, the return period does not account for any trend in the timeline.…”

“…Although there is a strong corpus of literature that describes how to perform non-stationary frequency analysis, its implementation is not without challenge. It is possible that the greatest challenge, as highlighted by St-Hilaire et al (2021), is the interpretation by managers of a return period in a non-stationary context, although some reflections are being carried out (Poff 2017). For Poff (2017), the non-stationarity of the hydrological regime needs to be anticipated in the management of environmental flows, and he proposes in particular to look at non-flow based parameters to assess the functions, processes and structures of lotic ecosystems.…”

“…Climate change models uncertainties aside, the results of this study are relevant for forward thinking about adapting the management of environmental flows, according to the evolution of the hydrological context with climate change effects. Although many jurisdictions, such as Quebec, still rely solely on hydrological metrics, hydro-climate change scenarios can provide an additional hydrological tool and allow for the implementation of holistic methods such as ELOHA (St-Hilaire et al 2021). This study showed that: (1) relatively homogeneous low flow regions are not matching with current hydrological regions and will shift in the future; (2) there is a need to calculate the flow metrics for the season(s) concerned by the management of water abstraction; and (3) using tools such as the wetted perimeter provides insight to the repercussion of flow changes in the physical habitat, mainly during the summer period.…”

“…Holistic methods, such as the Ecological Limits of Hydrological Alterations (ELOHA) framework (Poff et al 2010), can provide guidance by combining scientific and social processes and build consensus around the rules for prescribing environmental flows. This study will focus on hydrological and hydraulic methods, which can be included in some of the methodological steps of holistic methods, such as ELOHA, to assess the impacts of climate change (St-Hilaire et al 2021).…”

Special Issue: Past and Future Trends and Variability in Hydro-Climatic Processes

“…This special issue includes two invited critical reviews related to hydro-climatic processes associated with freshwater availability. Firstly, St-Hilaire et al [7] present how environmental flows (i.e., the amount of water required to sustain freshwater aquatic ecosystems) should be assessed in the context of a changing climate. They argue that three flow characteristics, namely quantity, timing, and quality, need to be minimally maintained for adequate environmental flows.…”