Drought in intermittent river and ephemeral stream networks

Abstract

Intermittent rivers and ephemeral streams (IRES), those watercourses that periodically cease to flow or dry, are the world's most widespread type of river ecosystem.Our understanding of the natural hydrology and ecology of IRES has greatly improved, but their responses to extreme events such as drought remain a research frontier. In this review, we present the state of the art, knowledge gaps and research directions on droughts in IRES from an ecohydrological perspective. We clarify the definition of droughts in IRES, giving recommendations to promote transferability in how ecohydrological studies characterize droughts in non-perennial stream networks. Based on a systematic search of the literature, we also identify common patterns and sources of variation in the ecological responses of IRES to droughts and provide a roadmap for further research to enable improved understanding and management of IRES during those extreme hydrological events. Confusion in the terminology and the lack of tools to assess the hydrological responses of IRES to drought may have hindered the development of drought research in IRES. We found that 44% of studies confused the term drought with seasonal drying and that those that measure droughts in a transferable way are a minority. Studies on ecological responses to drought in IRES networks are still rare and limited to a few climatic zones and organisms and mainly explored in perennial sections. Our review highlights the need for additional research on this topic to inform IRES management and conservation.

Ecohydrological interactions during drought

“…The first paper by Sarremejane et al (2022) reviewed the ecohydrological aspects of drought in intermittent rivers and ephemeral streams (IRES). The authors provided a drought definition for IRES and proposed several new indices that can be used for improving the understanding of feedbacks and links between hydrological stressors and the ecological response in IRES during droughts.…”

Extreme low‐flow effects on riverine fauna: A perspective on methodological assessments

“…Specifically, we define ELFs as low-flow events that exceed the severity or duration of those typically experienced at a particular location. Our definition is intentionally broad to account for studies adopting various hydrological criteria, such as between different climatic regions (Smakhtin, 2001), as well as those failing to define hydrological thresholds in ELF research (as with many ecological-focussed studies; see Sarremejane, Messager, & Datry, 2021). We also established our definition in accordance with the IPCC's definition of a 'hydrological drought' as 'a period of abnormally dry weather that persists for long enough to cause a serious hydrological imbalance … that propagate [s] over time into deficits in soil moisture, streamflow, and water storage' (IPCC, 2021, pp.…”

“…We define ELFs strictly from a hydrological perspective, while acknowledging that global perspectives and research on ‘drought’ have outlined that water deficits below normal conditions may be defined and characterised from other standpoints (e.g. meteorological, agricultural, socio‐economic and ecological; Sarremejane, Messager, & Datry, 2021; Van Loon, 2015). Specifically, we define ELFs as low‐flow events that exceed the severity or duration of those typically experienced at a particular location.…”

“…not driven by direct human activities such as water abstraction) as an ELF event. However, we recognise how ecohydrological research on naturally recurring flow cessation events in temporary rivers has dramatically improved our scientific understanding on how riverine fauna respond to flow conditions that commonly occur during ELF events (Sarremejane, Messager, & Datry, 2021).…”

Intermittency as an indicator of drought in streamflow and groundwater

“…It is seen that intermittency and drought have been studied separately although they are related to each other. Although fundamental hydrology knowledge suggests indeed that increasing droughts will increase intermittency in non-perennial rivers, there still exists a gap to better understand the relationship between the intermittency and various types of drought in non-perennial river basins which has been studied more in terms of ecohydrology (Kleine et al, 2021;Sarremejane, Messager, & Datry, 2021;Sarremejane, Stubbington, et al, 2021;Sauquet, Beaufort, et al, 2021). The significance of this study is the following hypothesis based on the so-called intermittency cycle (Figure 1), which is a novel concept aiming to better understand this relationship: Due to ever-increasing higher water demand of population and water-related sectors, water abstraction from rivers and groundwater withdrawal from aquifers increase day by day, groundwater level drops down, and it recharges rivers less.…”