Beyond binary baseflow separation: a delayed-flow index for multiple streamflow contributions

Abstract

Abstract. Understanding components of the total streamflow is important to assess the ecological functioning of rivers. Binary or two-component separation of streamflow into a quick and a slow (often referred to as baseflow) component are often based on arbitrary choices of separation parameters and also merge different delayed components into one baseflow component and one baseflow index (BFI). As streamflow generation during dry weather often results from drainage of multiple sources, we propose to extend the BFI by a delayed-flow index (DFI) considering the dynamics of multiple delayed contributions to streamflow. The DFI is based on characteristic delay curves (CDCs) where the identification of breakpoint (BP) estimates helps to avoid rather subjective separation parameters and allows for distinguishing four types of delayed streamflow contributions. The methodology is demonstrated using streamflow records from a set of 60 mesoscale catchments in Germany and Switzerland covering a pronounced elevation gradient of roughly 3000 m. We found that the quickflow signal often diminishes earlier than assumed by two-component BFI analyses and distinguished a variety of additional flow contributions with delays shorter than 60 d. For streamflow contributions with delays longer than 60 d, we show that the method can be used to assess catchments' water sustainability during dry spells. Colwell's predictability (PT), a measure of streamflow periodicity and sustainability, was applied to attribute the identified delay patterns to dynamic catchment storage. The smallest dynamic storages were consistently found for catchments between approx. 800 and 1800 m a.s.l. Above an elevation of 1800 m the DFI suggests that seasonal snowpack provides the primary contribution, whereas below 800 m groundwater resources are most likely the major streamflow contributions. Our analysis also indicates that dynamic storage in high alpine catchments might be large and is overall not smaller than in lowland catchments. We conclude that the DFI can be used to assess the range of sources forming catchments' storages and to judge the long-term sustainability of streamflow.

Including Regional Knowledge Improves Baseflow Signature Predictions in Large Sample Hydrology

“…The method is particularly sensitive to one parameter, the time window N over which the streamflow minima are calculated (default: days). To address this problem, Stoelzle et al (2020) calculated the BFI for a continuous range of time window values. They then used the obtained range of BFIs (which they termed Delayed Flow Index; DFI) to distinguish between different baseflow sources.…”

Groundwater and baseflow drought responses to synthetic recharge stress tests

“…Opposingly, baseflow dynamics can be seen as an integrated spatial signal, but uncertainties arising from the separation of baseflow from streamflow are large (e.g. Stoelzle et al, 2020a). Also, for other observational data, there are severe constraints (Gleeson et al, 2020).…”

“…Stoelzle et al (2014) developed a model-based stress test approach to study the sensitivity of streamflow to changes in climate based on modifications of the recharge. More applied syn-thetic stress-testing approaches often use worst-case scenarios to estimate the consequences of specific events (Stoelzle et al, 2020b). Stress-testing sensitivity to drought will help to better understand the degree of resilience of various hydrological systems (Hall and Leng, 2019).…”

“…As part of the Climate and Water Initiative of southern Germany's federal states (KLIWA), different types of stress tests or "what if" experiments were explored as means to better understand and more easily communicate potential future changes to low flow (Stoelzle et al, 2018(Stoelzle et al, , 2020b. Stress test designing included, for example, a progressive recharge reduction before the 2003 summer drought, as this event is often used as a planning benchmark or to assess followup costs: the stress tests ask whether the effect may even have been worse, e.g.…”

A novel method for cold region streamflow hydrograph separation using GRACE satellite observations

“…Despite these limitations, traditional hydrograph separation approaches are still widely used because of the modest data requirements and ease of implementation. Recent improvement in hydrograph separation includes new parameterisation strategies (Pelletier and Andréassian, 2020) and recognition of multiple baseflow components in the streamflow (Curtis et al, 2020;Stoelzle et al, 2020). Nevertheless, since traditional hydrograph separation methods are based on a number of simplifications and assumptions that limit their applicability, previous studies have widely recognised that more effort is required to evaluate the limitations and their effects, and when possible, the methods should be combined with other methods and data to address these limitations (Hooper and Shoemaker, 1986;Stewart et al, 2007;Rosenberry and LaBaugh, 2008;Miller et al, 2014;).…”