Correlations between meteoric forcings and groundwater levels in a karst aquifer well

This study uses two complementary black-box approaches to obtain information about the time response of groundwater levels (output) from a well in the Salento Miocene karst aquifer (southern Italy), subjected to the meteoric forcings of precipitation and atmospherc pressure (inputs). First, a Langevin equation is used to infer the shape of the output correlation functions when forced by two correlated random inputs (a pure random process as precipitation and an exponentially correlated process as atmospheric pressure). Then, a transfer function model is applied to obtain least square response function coefficients for cross-correlograms of the measured groundwater levels, the precipitation or net infiltration and the atmospheric pressure, which has a relevant effect on the groundwater fluctuations and is cross-correlated to the precipitation. The cross correlograms between output and inputs have been reconstructed with the aim to disentangle the effects of the observed meteoric inputs on the groundwater levels. Thus, the effect of the correlations in the transfer function inputs is discussed and the inferred results for the groundwater level dynamics are outlined in both the time and the frequency domain. Both approaches suggest the attribution of the short-term maxima in the input-output cross correlograms to the correlations between the input forcings. Consequently, a delayed medium-term response of about 80 days duration in the groundwater level is attributed to the net infiltration forcing, as result of the least square response function approach.