Riparian evapotranspiration shapes stream flow dynamics and water budgets in a Mediterranean catchment

Abstract

15Riparian trees can regulate stream flow dynamics and water budgets by taking up large amounts of water from both soil and groundwater compartments. However, their role has not been fully recognized in the hydrologic literature and the catchment modeling community. In this study, we explored the influence of riparian evapotranspiration (ET) on stream flow by simulating daily stream exports from three nested Mediterranean sub-catchments, both including and excluding the riparian compartment in the structure of 20 the PERSiST rainfall-runoff model. The model goodness of fit significantly improved with the inclusion of the riparian compartment, especially during the vegetative period when, according to our simulations, riparian ET reduced mean daily stream flow by 26%. Moreover, sensitivity analyses suggested that riparian ET was a significant hydrological process contributing to stream flow recession in summer. At the catchment scale, simulated riparian ET accounted for 7% of annual water depletions, its contribution 25 being especially noticeable during summer (8-19%). Simulations considering future climate change scenarios suggest that longer vegetative periods would result in higher contribution of riparian ET to annual water budgets. Annual increases in riparian ET ranged between 2 and 13% from the most conservative to the most extreme drought scenarios. Overall, our results highlight that a good assessment of riparian ET is essential for understanding catchment hydrology and stream flow dynamics in 30 Mediterranean regions. Thus, the inclusion of the riparian compartment in hydrological models is strongly recommended in order to establish proper management strategies in water-limited regions.