Evaluating changes in water levels during periods of normal flow and drought with a specific emphasis on water withdrawal

ABSTRACT Egirdir Lake, situated in southwestern Türkiye, is critical as the country's second-largest source of drinking water. Climate change poses serious threats to it, particularly droughts that have recently caused its water levels to drop. This research aims to forecast potential changes in the lake's water levels under normal and drought conditions. It also evaluates the effectiveness of various mitigation measures, identified with stakeholder input, to safeguard water security. A key challenge of this study is the lack of comprehensive hydrological data for the lake's drainage basin. The AQUATOOL+ Decision Support System's SIMGES water management and EVALHID hydrological modeling modules were used to address this. Initially, naturalized flows in the basin were simulated to determine inflows. Subsequently, altered flows and changes in water levels were assessed under different water extraction and discharge scenarios. Subsequently, simulated natural runoff and observed water level data were analyzed to establish a reference drought condition for projecting water levels during drought scenarios. Finally, projections for water levels were developed for current and drought scenarios, considering various mitigation alternatives. The study concludes that Alternative 3 is the optimal choice, effectively maintaining water levels within acceptable limits with minimal impact on agricultural irrigation, across both scenarios.