The Impact of Potential Evapotranspiration Methods on Future Hydrological Cycle Intensification Across European Catchments 

Potential Evapotranspiration (PET) is a crucial component in hydrological modelling. It represents the water demand of the region, and thus, it can influence drought assessments, partitioning of precipitation to evapotranspiration (Budyko framework), and climate change impact studies. Many studies have focused on the impact of PET on future runoff changes, with limited consideration of other hydrological components (actual evapotranspiration, runoff, soil moisture, and total water storage). However, few studies examine how different PET methods affect future changes in hydrological cycle components. Understanding these impacts and uncertainties is crucial for the intensification of hydrological cycle studies. This study aims to investigate the impact of potential evapotranspiration on the intensification of the hydrological cycle for the future across European catchments covering all European climates. A mesoscale Hydrological Model (mHM) is employed to assess hydrological cycle components for each catchment. Five ISIMIP climate models were used to simulate historical (1950-2014) and future (2015-2100) hydrological cycle components for three Shared Socio-economic Pathways (SSPs): SSP1-2.6, SSP3-7.0, and SSP5-8.5. Twelve widely used PET methods were considered, ranging from the simplest (temperature-based) to the most complex approaches (radiation and combinational-type). In total, 557 catchments from energy-limited, mixed, and water-limited categories were analyzed. Our initial analysis reveals that annual-scale hydrological cycle components simulated by all climate models are broadly consistent with historical observation-based datasets of Thakur et al. (2024). At the monthly scale, temperature-based PET methods demonstrate greater variability than radiation and combination methods. In summer, complex PET methods overestimate mean monthly PET, while temperature-based methods align better with observations. Our findings improve the understanding of the potential evapotranspiration’s role in the future hydrological cycle intensification and its associated uncertainties across European catchments.Reference: Thakur, V., Markonis, Y., Kumar, R., Thomson, J. R., Vargas Godoy, M. R., Hanel, M., and Rakovec, O.: Unveiling the Impact of Potential Evapotranspiration Method Selection on Trends in Hydrological Cycle Components Across Europe, Hydrol. Earth Syst. Sci. Discuss. [preprint], https://doi.org/10.5194/hess-2024-341, in review, 2024.