Groundwater level response to precipitation at the hydrological observatory of Pinios (central Greece)

To study groundwater dynamics and their response to precipitation in the Pinios river basin (central Greece), the variation trends and seasonal patterns of fourteen monitored groundwater and two precipitation time series were examined using time series decomposition, autocorrelation, and wavelet analysis. The objective is to perform indirect methodologies based on groundwater level and precipitation data to attain a detailed understanding of the hydrogeological mechanisms of the aquifer system and develop an approach that can be easily employed worldwide. The three approaches confirm local groundwater circulation understanding by dividing the aquifer system into three parts characterised by varying transmissivity and storativity properties. The extended memory effect, ranging between 70 and 230 days suggests great inertia and storage capacity of the examined groundwater system. The wavelet analysis proves that the system acts as a filter which absorbs the precipitation frequencies converting them into GWL signals, as demonstrated by the 256 days periodicity shared by groundwater level and precipitation time series. Generally, GWLs present a hysteresis to precipitation due to the geological setup and local flow conditions and are particularly affected by a seasonal component, as also highlighted by time series decomposition. An evident annual periodicity is also observed in hydrological and hydrogeological time series. Results suggest the effectiveness of the proposed combination of methods in developing hydrological understanding and their general applicability to other regions where at least groundwater level and precipitation time series are available. By utilising such data-driven approaches, hydrogeologists and water resource managers can gain valuable insights into the behavior of aquifers, groundwater flow patterns, and the impact of human activities on groundwater quality and quantity.