A Preliminary Model of Lake Toba’s Water Level Using System Dynamics

Abstract

This study develops a preliminary System Dynamics (SD) model to characterize the hydrological behavior of Lake Toba by integrating natural  and anthropogenic water-balance components into a unified stock–flow framework. The model incorporates precipitation, runoff, baseflow, groundwater exchange, evaporation, regulated outflow, and sectoral water withdrawals to represent the dominant processes controlling lake-storage dynamics. Using monthly data from 2000 to 2020, the model simulates variations in lake volume and water-level elevation, reproducing the seasonal rise during wet periods and decline during dry periods, as well as revealing a gradual long-term downward trend. Sensitivity analysis identifies precipitation as the most influential driver of lake-level change, while evaporation and outflow function as stabilizing mechanisms that regulate storage. Anthropogenic withdrawals show relatively minor effects under current conditions but may become increasingly important under higherdemand scenarios. Overall, this preliminary model provides a transparent analytical foundation for understanding the feedback structure governing Lake Toba’s water balance and offers a basis for future policy-oriented simulations aimed at supporting sustainable lake-water management.