Simulating streamflow in Mediterranean environment with SWAT+ for setting an environmental flow

The aim of this work is to set the environmental flows (EFlow) of the Locone stream downstream of the reservoir by using a hydrological method. To compensate for the lack of hydrological and ecological data, which characterizes the river, the open-source Soil and Water Assessment Tool Plus (SWAT +) model was tested for simulating streamflow in un-impacted conditions. SWAT + is a completely revised version of the SWAT model. The study area is the Locone river basin (219 km2) located in southern Italy. The climate is typically the Mediterranean. The flow regime shows a pattern of low flow and zero flow in summer. The Locone is classified by the River Basin Authority as a temporary river. Upstream of the dam, the streamflow was measured from 1971 to 1983 with several missing data. The main land use is winter wheat (64% of the total area), followed by broad-leaved woods (6.6%) and broad beans (5.4%). The hydrological pressures in the basin are point source discharges and the Locone dam. The dam was built in 1986 for agricultural purposes (approximately 5,000 hectares are irrigated) and for a hydroelectric power station (1,693,000 kwh / year i). In this work, the SWAT + model was applied with the aim of simulating daily streamflows in un-impacted conditions in the river section upstream the dam for a period of 50 years (from 1971 to 2020). The model was calibrated (NSE = 0.720; Pbias = -11.514 and R2 = 0.84) and validated (NSE = 0.42; R2 = 0.45; Pbias = -12.5) including point sources. After that, the model was run excluding the point sources to simulate unimpacted conditions. The simulated daily flow data (un-impacted) were used to calculate several hydrological alteration indicators (IHAs) over the study period. The IHAs were used to characterize the flow regime and to set the EFlow by fixing each of the selected indicators within the interquartile range. This set of Eflow should be revised on the basis of ecological data.