Revisiting the Thornthwaite-Mather method to characterize drought impacts on groundwater recharge in Greece

This study revisits the Thornthwaite – Mather (T-M) method to estimate groundwater recharge in Greece under prolonged drought conditions, with the aim of quantifying recharge dynamics and identifying long-term trends in renewable groundwater resources. The constraints of applying the T-M approach for recharge estimation were addressed through the integration of recently developed large-scale datasets on soil properties, including soil water content at field capacity and wilting point, combined with climate reanalysis datasets on precipitation, evapotranspiration and surface runoff. The results indicate that groundwater recharge has been steadily decreasing over the past 25 years, with a particularly alarming trend in recent years, where Greece has lost approximately 54% of its mean annual renewable groundwater recharge compared to the 2001 - 2005 average. These findings highlight the importance of revisiting classical water balance methods with modern datasets to inform water resource management and adaptation strategies in drought-prone regions.