Climate-Driven Water Stress and the Role of the Energy Transition in Enhancing Water–Energy Nexus Resilience

Water and energy are two essential and interdependent resources that form the foundation of modern civilization. In Germany, the energy sector accounts for the largest share of total water demand (39% in 2022). Bavaria has traditionally been considered a water-rich federal state, with total water withdrawals historically remaining below 10% of available water resources. However, these conditions may change in the future, as climate change alters hydrological regimes and increases the frequency and severity of drought events. In this context, it is necessary to assess the resilience of regional water and energy systems under future climatic, demographic, and structural changes in the energy sector.

This study investigates the water–energy nexus and water security in the Upper Main River basin (Bavaria, Germany). The analysis is conducted within the framework of the RETOUCH Nexus project using an integrated modeling approach that combines the Soil and Water Assessment Tool (SWAT+), the Water Evaluation and Planning System (WEAP), and the Low Emission Analysis Platform (LEAP). SWAT+ is applied to simulate future hydrological changes under different climate scenarios derived from the ISIMIP3b dataset, while WEAP is used to represent sectoral water demands. Energy system transitions aligned with Bavaria’s 2040 climate neutrality targets are represented through LEAP, capturing feedbacks between electricity generation, renewable energy expansion, and water use in the energy sector.

The results indicate that the Upper Main River basin experiences seasonal unmet water demand, especially during summer months, with water availability declining under climate change. The SSP5–8.5 scenario represents the worst-case combination of reduced water availability and increased demand. Future unmet water demand emerges primarily in the industrial and energy sectors. However, the transition toward renewable energy—particularly wind and solar power—offers substantial potential to reduce water consumption in electricity generation, thereby increasing the resilience of the energy sector to climate change. Overall, this study provides a robust basis for forward-looking, climate-resilient water management and policymaking within Bavaria’s evolving environmental and energy system.