Response of Pinios hydrologic observatory (Agia basin-Thessaly, Greece) to storm Daniel

Extreme weather events are becoming increasingly frequent and intense due to climate change, posing significant challenges to water resource management in vulnerable agricultural regions. Understanding how aquifer systems respond to such events is critical for ensuring long-term groundwater sustainability. Continuous, high-resolution monitoring is essential to capture the dynamics of recharge processes, particularly during intense storms. This study presents novel observations from the Pinios Hydrological Observatory (PHO), located in the Pinios River Basin in Thessaly, Greece one of the country's most important agricultural areas, heavily dependent on groundwater for irrigation. The PHO, part of the Greek Long-Term Ecological Research Network, is equipped with automated sensors that provided rare, event-scale data during Storm Daniel, a major hydrometeorological event that impacted the region in September 2023. The sensors recorded the passage of the flood wave in near-real time, enabling a detailed analysis of groundwater recharge dynamics. Hourly groundwater level data from fourteen monitoring wells were analysed in conjunction with meteorological data using advanced time-series techniques, including Dynamic Time Warping (DTW), to detect temporal shifts in aquifer response. Lag times between rainfall and groundwater rise ranged from 3 to 10 days, depending on local hydrogeological conditions. Piezometric surface maps generated through Inverse Distance Weighting (IDW) interpolation highlighted widespread recharge across alluvial deposits, with groundwater levels increasing from approximately 70 to 72.2 m above sea level in some areas. These results underscore the value of real-time monitoring networks in capturing aquifer responses to extreme events, contributing to more informed and adaptive water management strategies.