Environmental Flow Assessment in Greece’s Major Rivers Using LISFLOOD Large-scale Model and Hydrology-based Methods

Abstract Assessing the environmental or ecological flow (EF) of rivers constitutes a crucial endeavor in safeguarding them against increased overexploitation, climate change impacts, and the proliferation of dams along their courses. However, the frequent lack of observation data jeopardizes the accurate and reliable assessment of rivers’ minimum streamflow requirements. The research implements a methodological framework to estimate EF in partially gauged basins by forcing the Tennant, Tessman and the Global Environmental Flow Calculator EF methods with river discharges generated by the LISFLOOD large scale hydrological model over a 31-year period (1992–2022). The outputs which correspond to nine major rivers in Greece, many of which are transboundary ones, are compared to the environmental flow estimates derived from the Greek legislation model. The findings indicate that the Greek legislation produces low EFs on an intermonthly timescale, often aligning with the EFs from other methods during the dry season, suggesting the need for a revision of the current legislation. The Tennant method tends to yield relatively low EFs in the dry period, whereas the Tessman and Global Environmental Flow Calculator methods produce EF curves that closely mimic the natural streamflow curve of each river. The methodological framework presented here is adaptable to any hydrosystem, offering a valuable base for enhanced EF assessment in the future.