Active subsurface storage as a resilience factor of Luxembourgish catchments under a changing climate

The Budyko framework is widely used in hydrology to describe how long-term catchment behaviour is constrained by the balance between annual precipitation (the water budget) and the evapotranspiration capacity (the energy budget). These two factors jointly determine a catchment’s position on the Budyko diagram. Under a stationary climate, this position is expected to fluctuate around an equilibrium state; under climate warming, this equilibrium may shift.

Combining experimental and operational stream gauge networks with remote-sensing products, we analyse the positions of 61 catchments in Luxembourg on the Budyko diagram over the period 1995–2025. Owing to its relatively homogeneous climate, Luxembourg provides a particularly suitable case study for isolating the influence of non-climatic controls on these positions, such as geology and its underlying contribution to storage capacity.

Our results show that departures from the Budyko curve are explained by differences in active catchment storage, which are closely linked to geologic variations. Catchments with higher active storage capacities tend to plot above the Budyko curve, remain closer to an energy-limited regime, and are therefore less exposed to drying. This analysis highlights the role of catchment geology, and more specifically its capacity to store and release water over multiple years, as a key resilience factor of the water cycle under a warming and increasingly arid climate.