Correlation between groundwater levels and meteorological indicators in the coastal karst aquifer of Salento (Southern Italy)

In many regions of the Mediterranean basin, both climate variability and human pressure threaten groundwater quality and quantity. Uncertainties concerning future precipitation, temperature patterns, and water accessibility provide a challenge in understanding how groundwater reacts to the variability of the hydrological forces. This aspect is of fundamental interest for water resources planning and management, especially in those areas where groundwater is the main water source. The proposed research looks for correlations between meteorological drought indexes and groundwater levels (GWLs) to provide qualitative information about GWLs response to precipitation and temperatures changes. The GWLs time series refer to nine monitoring wells located in the coastal karst aquifer of Salento (Puglia, Southern Italy). The aquifer is challenging because of the highly complex geological, geomorphological, and hydrogeological structure and regional size. In such complex environment and under climate changes, a high and unrestricted exploitation for irrigation, industrial, and drinking purposes may deteriorate the qualitative and quantitative status of groundwater. Such features often prevent the recognition with sophisticated methods of the relationship between hydrological and hydrogeological time series, especially under data scarcity. Searching for these relationships, three correlation coefficients were applied at different time scales, with reference to the period between July 2007 and December 2011, between the SPI (Standardized Precipitation Index) and SPEI (Standardized Precipitation and Evapotranspiration Index) and GWLs time series. Results of the three coefficients outline a positive and statistically significant correlation between time series, generally for long time scales, highlighting the slow response of GWLs to precipitation. Despite the complexity of the aquifer, it linearly reacts to precipitation and temperature variability in the long term, acting as a low-pass filter with a notable inertial behavior in response to meteorological events. The aquifer response is different compared to dry and recharge periods. In most cases, the decreasing GWL courses agree with the dry SPI and SPEI ones, while the increasing GWL courses are less congruent during wet periods. This characteristic reveals crucial in defining correct measures of protection and safeguard of groundwater resources during periods of meteorological drought.

Results suggest that the selected approaches are worthy of interest for those areas characterized by severe stress conditions due to long drought periods and under excessive groundwater exploitations, demonstrating the generality of their applicability also under data scarcity.