Process-Based Vegetation Models Improve Karst Recharge Simulation Under Mediterranean Forest

Assessing underground hydrosystem recharge is crucial to characterizing their hydrogeological functioning. The common questions arising from a poor understanding of hydrogeological mechanism are about parts of the gross rain amount that evapotranspire and get temporarily stored within the soil. Evapotranspiration and soil water storage are largely influenced by the structure and the function of the aboveground vegetation, which is generally composed of heterogeneous forest layer in Mediterranean karstic systems. However, most models used to compute karst hydrosystem recharge rely on simplistic formulations of evapotranspiration (ET) that do not account for vegetation functioning. In this study, we used the vegetation process-based model CASTANEA to improve water transfer in the higher horizon of the karst system and recharge simulations. Effective infiltration was computed with CASTANEA or with a classical approach (based on precipitation minus ET) for a well-documented holm oak site in southern France. We then compared simulation results with outflow data measured at 33 m below ground. We found significant differences between the two calculation methods, up to 200 % of annual recharge in the case of a very dry year. The comparison of modelled effective infiltration with outflow data indicated that using CASTANEA improved assessment of the temporal dynamics of water recharge in this karst system compared to a more classical approach. Our approach constitutes a promising way to improve the simulation of karst hydrosystem recharge.