Coupled RRI–WEAP framework for integrated water balance and quality assessment under climate change and population growth in Abou Ali River basin

ABSTRACT This study evaluates the long-term water balance and water quality of Abou Ali River Watershed in North Lebanon under the combined impacts of climate change and population growth. An integrated modeling framework was applied, coupling the Water Evaluation and Planning (WEAP) model for water demand, supply, and groundwater dynamics with the Rainfall–Runoff–Inundation (RRI) model to simulate surface hydrology. Climate change impacts were assessed using CMIP6 projections under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5). The analysis is constrained by limited ground-based hydro meteorological and water quality data, requiring reliance on modeled outputs and secondary datasets. Simulation results indicate that total water demand increases from 407 MCM in 2015 to 785.79 MCM by 2100, while available water supply declines to 313.39 MCM, leading to an unmet demand of 472.40 MCM. Groundwater storage is projected to decrease by approximately 41%, reflecting unsustainable extraction rates. Water quality modeling reveals substantial degradation, with total dissolved solids exceeding 1,000 mg/L and biochemical oxygen demand (BOD₅) reaching 65 mg/L, primarily due to untreated wastewater discharge and reduced dilution capacity. An integrated sustainable management scenario incorporating demand management, wastewater treatment, and improved irrigation efficiency significantly improves both water balance and water quality. These findings highlight the urgent need for adaptive and integrated water resource management strategies to enhance long-term water security in the watershed.