Effective water resources management is critical to ensure sustainable development in hydrogeological basins where complex interactions between surface water and groundwater play an essential role. This study used the Water Assessment and Planning (WEAP) model as a decision support tool for comprehensive basin-scale water resource planning for the İzmir Torbalı-Fetrek sub-basin (TFS), Türkiye. Urban sprawl occurs in the Quaternary Alluvium. The amount of groundwater consumption is expected to increase over the years.

The baseline scenario (BS) was created using projection based on field data to form a reference for future predictions. Total annual groundwater consumption was estimated for industrial, domestic, and agricultural activities for the year 2021, which was taken as starting date for projections into the future. The BS includes human population, number and capacities of wastewater treatment plants, industrial structures and their water needs, observation well dataset, and river flow measurement results in the TFS. Hydrological modeling was performed using the Soil and Water Assessment Tool (SWAT), and groundwater flow modeling using MODFLOW. Water availability components such as groundwater recharge and streamflow discharge rate were obtained from SWAT model results, then used in the WEAP program as input, subsequently MODFLOW was linked to WEAP. The WEAP model was run in two future climate change scenarios (RCPs 4.5 and 8.5).

Three optimistic management scenarios have been developed via the WEAP model to reduce groundwater use by 2050. These are categorized as reducing municipal water consumption, reusing wastewater, and increasing aquifer recharge by Managed Aquifer Recharge (MAR). Optimistic management scenarios for two different climate projections were used to assess the projected changes in groundwater levels and the supply-demand balance by 2050.

This study is supported by the PRIMA program (European Union) under grant agreement No:2024 Project