Addressing the complexity of non-perennial river ecosystems in environmental flow planning

Human reliance on surface and groundwater often conflicts with the conservation of freshwater ecosystems. Environmental flows (e-flows) were introduced to protect and restore river ecosystems by regulating water use and flow. Initially conceived as constant minimum flows, e-flows now account for the natural hydrological variability of rivers, as well as their ecological and social dynamics. However, methods to design e-flows were originally developed for perennial rivers and are often unsuitable for non-perennial rivers due to their complex flow regimes, their often reliance on groundwater and the need for alternative ecological indicators beyond fish. Consequently, management cases of e-flows for non-perennial rivers remain scarce. This study aims to highlight and discuss the main challenges in establishing the hydrological, geomorphological, water quality, ecological, and sociocultural foundations for assessing e-flows in non-perennial rivers and to outline research pathways for advancing this emerging field.