Mapping Europe’s Net-Zero Trade-offs: An Open Integrated Model of Energy, Land, and Water Systems

CLEWs-EU, an open-source Integrated Assessment Model developed to analyse the coupled climate–land–energy–water (CLEWs) system of the European Union within a single, internally consistent optimisation framework, is presented here. Implemented in OSeMOSYS, the model identifies least-cost system configurations that satisfy exogenously defined energy service demands across electricity and heat supply, buildings, industry, and transport, while simultaneously accounting for land availability, crop production, livestock, forest dynamics, water withdrawals, and climate-sensitive resource constraints. The energy system representation includes primary energy supply, renewable and thermal generation, electricity storage, hydrogen production, and cross-border electricity exchange, with intra-annual time slices capturing seasonal and daily variability in demand and renewable output. The land and water components represent crop types by irrigation class, biomass production, water supply and withdrawals by sector, and land allocation among cropland, pasture, forest, and other uses. Explicit linkages connect irrigation demand, hydropower availability, thermal cooling requirements, and biomass flows into the energy system, enabling assessment of system-wide trade-offs and feedbacks. Baseline projections to mid-century indicate a strong shift toward electrification across end-use sectors, driven primarily by the expansion of renewable electricity generation and the increasing deployment of heat pumps in buildings. Electricity generation is increasingly dominated by wind and solar, supported by storage and intercountry balancing through expanded interconnections. Final energy demand in buildings declines due to efficiency improvements and renovation measures, while transport activity shifts toward electric and, in specific modes, hydrogen-based technologies. Hydrogen supply grows over time, with both domestic production and imports contributing to end-use consumption, particularly in transport and industry.

Land-use dynamics reflect increasing competition between food production, biomass supply for energy, and forest-based carbon sequestration. Crop production evolves through shifts in land allocation and irrigation practices, while water withdrawal patterns change substantially across sectors and countries, with agriculture remaining the dominant user in water-stressed regions. Water constraints influence both agricultural output and energy pathways, including hydropower generation and thermal plant cooling. Emissions trajectories vary markedly by sector, with faster declines in power generation and slower reductions in agriculture and certain industrial processes, highlighting persistent mitigation challenges beyond the electricity system.