Variability patterns of the annual frequency and timing of low streamflow days across the United States and their linkage to regional and large‐scale climate

Abstract

Low-flow events can cause significant impacts to river ecosystems and water-use sectors; as such, it is important to understand their variability and drivers. In this study, we characterise the variability and timing of annual total frequency of lowstreamflow days across a range of headwater streams within the continental United States. To quantify this, we use a metric that counts the annual number of lowflow days below a given threshold, defined as the cumulative dry days occurrence (CDO). First, we identify three large clusters of stream gauge locations using a Partitioning Around Medoids (PAM) clustering algorithm. In terms of timing, results reveal that for most clusters, the majority of low-streamflow days occur from the middle of summer until early fall, although several locations in Central and Western United States also experience low-flow days in cold seasons. Further, we aim to identify the regional climate and larger scale drivers for these low-streamflow days.

Seasonality and Drivers of Low Flows Across Europe and the United States

“…Very few catchments have low flows that occur in the period April through June (Figure 1). Similar distinct summer and winter low flows have been reported for regions within Europe (e.g., Demirel et al, 2013;Laaha & Blöschl, 2006b;Tongal et al, 2013;Van Loon et al, 2015;Wehren et al, 2010) and for parts of the US (e.g., Cooper et al, 2018;Dierauer et al, 2018;Pournasiri Poshtiri et al, 2019).…”

“…Low‐flow timing has previously been analyzed for several catchments and regions (e.g., Burn et al., 2008; Garbrecht et al., 2004). For example, low‐flow seasonality has been studied across Switzerland (Wehren et al., 2010), the United Kingdom (Young et al., 2000), Austria (Laaha & Blöschl, 2006b), the United States (Pournasiri Poshtiri et al., 2019), and parts of eastern Germany (Fangmann & Haberlandt, 2019). Low‐flow seasonality has been used for regionalization purposes and to assess climate change impacts (e.g., Laaha & Blöschl, 2006b; Demirel et al., 2013; Vezza et al., 2010).…”

Anthropogenic Drought: Definition, Challenges, and Opportunities

“…As human water demands increase in areas that depend on the snowpack, years of low snowpack accumulation can enhance downstream anthropogenic drought effects and such intensification must be better understood for improving water resources management, minimizing ecosystem stress, etc. A reduced snowpack necessitates the adjustment of water management practices due to less spring snowmelt‐derived runoff and shifts from snow to rain (and earlier runoff), which have already been observed due to increases in temperature (Hatchett & McEvoy, 2018; Huning & AghaKouchak, 2020; Li et al., 2017, 2019; Pournasiri et al., 2019; Qin et al., 2020; Tang et al., 2019). Water managers need to consider storing more water earlier in the season while also weighing storage capacity considerations necessary for minimizing flood risk.…”

Trends in flow intermittence for European Rivers

“…For low flows and droughts, regional classifications at the European scale (Stahl and Demuth, 1999, Hannaford et al, 2010, Kirkby et al, 2011 or national scale (in Spain, Coch and Mediero, 2016) have been produced using most often the flow exceeded 90% of the time as a threshold for low flows or drought periods. Only a few classifications of intermittent rivers based on zero flow indicators have been proposed, in an attempt to relate their spatiotemporal variability with catchment characteristics or climatic variability (Kennard et al, 2010, Snelder et al, 2013, Eng et al, 2015, Perez-Saez et al, 2017, Tzoraki et al, 2016, De Girolamo et al, 2014, Dörflinger, 2016, Pournasiri Poshtiri et al, 2019. Identifying homogeneous regions and the drivers of flow intermittence, in terms of seasonality, catchment or climatic properties, could help to estimate intermittence characteristics and trends at the regional level (Pournasiri Poshtiri et al, 2019).…”

“…Only a few classifications of intermittent rivers based on zero flow indicators have been proposed, in an attempt to relate their spatiotemporal variability with catchment characteristics or climatic variability (Kennard et al, 2010, Snelder et al, 2013, Eng et al, 2015, Perez-Saez et al, 2017, Tzoraki et al, 2016, De Girolamo et al, 2014, Dörflinger, 2016, Pournasiri Poshtiri et al, 2019. Identifying homogeneous regions and the drivers of flow intermittence, in terms of seasonality, catchment or climatic properties, could help to estimate intermittence characteristics and trends at the regional level (Pournasiri Poshtiri et al, 2019). Indeed, these intermittent and ephemeral streams are underrepresented in monitoring networks and often ungauged in Europe (Skoulikidis et al, 2017, Costigan et al, 2017.…”