Seasonal streamflow variability and surface water assessment in the Ia Lo^p and Ia H'leo basins of the Ea Súp semi-plain, Central Highlands of Vietnam

Introduction The Ea Súp semi-plain in Vietnam's Central Highlands is a drought-prone agricultural region where seasonal water scarcity increasingly constrains food production, water regulation, and downstream water supply. Methods This study assesses surface water availability and seasonal streamflow variability in the Ia H'leo and Ia L o ^ ́ p basins using the MIKE-NAM rainfall-runoff model. Reliable reservoir-inflow observations for 2019–2022 were used for calibration and validation, while rainfall and evaporation inputs were available for 1980–2022. Model performance was evaluated at the monthly scale using NSE, PBIAS, KGE, volume errors, and flow-duration curves. The calibrated model was then applied to reconstruct monthly streamflow for 1980–2022. Results Model performance was generally acceptable to good, with NSE values ranging from 0.73 to 0.95 and KGE values from 0.68 to 0.82, although dry-season biases remained in some basins. The results indicate a strongly seasonal hydrological regime, with the June–October flood season contributing 71–93% of annual runoff. The reconstructed series also suggests distinct multi-decadal wet and dry phases, including a prolonged dry period from 1990 to 2008 followed by a wetter interval during 2009–2019. Discussion From a Water-Energy-Food (WEF) nexus perspective, the results provide a quantitative basis to improve reservoir operation, irrigation planning, and water-allocation strategies under data-scarce conditions. The findings also support the integration of structural measures with Nature-based Solutions, such as headwater forest restoration and wetland protection, to enhance natural flow regulation, reduce dry-season water stress, and limit cross-sectoral competition for water resources.