Temporally compounding energy droughts in European electricity systems with hydropower

As Europe’s renewable energy capacities expand, electricity systems face increased risks of energy droughts—periods of low production coinciding with high demand. We evaluate characteristics of electricity variability due to weather variations by calculating 1,600 years of daily production and demand. Focusing on five European countries—chosen for their energy mix including hydropower—we find that energy droughts result from processes that cause (temporally) compounding impacts in the energy and meteorological system. These can turn what might have been short-term droughts into prolonged high unmet energy demand. For instance, low reservoir inflows in spring quadruple the chance of prolonged energy droughts: reduced snowpack and rainfall lower hydro availability but also dry out subsoils, increasing the chance of heatwaves and therewith extending the energy problems into summer. We identify and quantify three compounding energy/climate conditions and the associated characteristics and risks of multi-year energy droughts, crucial for informing future energy system design.