Updating of Traditional Groundwater Budget and Recharge Assessment by Using the APLIS Method for the Karst Scirca Spring (Central Italy)

A comparison between the values of mean annual recharge to the karst Scirca spring (Umbria-Marche Apennines, Central Italy), estimated by the Turc method and the multi-parametric APLIS method, was carried out. The APLIS method was first used to evaluate the aquifer recharge in the 1959–2001 period, as for this interval the spring water budget was previously evaluated by using the Turc formula. The results of both methods were compatible with each other. According to the discharge data available at the time, the Turc method indicated that the water surplus was about 65% of rainfall and that about 14% of water surplus was converted into runoff. The recharge calculated by the APLIS method for the same period corresponds to 62% of rainfall, roughly matching the mean annual discharge. The comparison among the two methods was repeated for the 2010–2022 period, since in the former analysis there were uncertainties about the natural spring discharge and the evaluated mean annual rainfall. The Turc method was used to evaluate mean annual evapotranspiration (ETR) in 2010–2022. ETR, estimated by adding to the rainfall amount the snow contribution, resulted to be 38% of the mean annual precipitation. The mean annual water surplus is therefore 62% of precipitation and equals the mean annual discharge of Scirca spring. According to these new results, runoff is therefore negligible. Mean annual recharge was then determined by APLIS. Results indicate that the percentage of annual precipitation contributing to recharge is 61%, very close to the mean annual discharge of Scirca spring and to the water surplus determined by the Turc method.