Karst Vadose Zone Hydrology Explored Through Cave Drip Water Dynamics: The Roles of Soil, Epikarst and Climate

Diffuse groundwater recharge through soil, epikarst and host rock remains one of the least understood processes in karst hydrogeology. Here we present a three‐year, high‐resolution cave drip rate record from a mid‐latitude continental karst cave in Croatia. Based on characteristic drip rate patterns, monitored drip sites cluster into three categories. The first shows almost constant, low drip rates, indicating recharge from the host rock matrix. The second displays clear seasonality, with synchronous drip rate increases in late autumn and early winter. These increases lag by 2–3 months behind declines in potential evapotranspiration and increases in soil moisture content, reflecting additional filling of epikarst storage before recharge reaches these drip sites. The third type shows constant low drip rates interrupted by sharp increases, indicating combined matrix and fracture flow, with rapid responses linked directly to the soil water reservoir. A rainfall recharge threshold approach, widely applied in previous studies, fails to predict recharge dynamics across drip sites and seasons, highlighting its limited applicability at this study site. To explore the observed non‐stationary recharge dynamics and to account for the large soil and epikarst storage effect we employed a soil–epikarst water balance model. Model calibration against observed drip rate time series reveals a combined soil and epikarst storage capacity of about 440 mm, where roughly two‐thirds of the total storage capacity resides in the epikarst. Together, the observed data and modelling results emphasise the central role of soil and epikarst storage in controlling karst vadose zone recharge and underpin interpretations of karst hydrological processes and speleothem‐based palaeoclimate reconstructions.