Long-Term Annual Average Aquifer Recharge assessment for the island of Sardinia (Italy)

Claudio Arras;Giorgio Ghiglieri;Stefania Da Pelo;Cristina Buttau;Mario Lorrai;Maurizio Testa

2021-01-01

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Abstract

Evaluation of Long-Term Annual Average Recharge (LTAAR) is a challenge for sustainable management of groundwaters. Despite many methods were developed based on different kind of input dataset, inverse water balance is one of the most effective approach when long term climatic data series are available. In this work, the inverse water balance for all the aquifers of the Hydrographic District of Sardinia (Arras et al. 2019) is presented. The proposed model adopts a geographically based integrated evaluation system. Daily precipitation and temperatures data from the official weather stations network of Sardinia was collected for the periods 1981-2010 and 2009-2018, while average precipitation and temperature maps, elaborated by the Sardinian Regional Agency for Environmental Protection (ARPAS: Hydro-meteoclimatic Department), were used for the period 1971-2000. Elevation data comes from the 10 m grid Digital Terrain Model (DTM) of Sardinia, downscaled to a 40 meters grid. Daily measurements were used to calculate climate Normal according to the World Meteorological Organization guidelines (WMO 2017). Spatial interpolation of punctual Normal was performed through the application of the ordinary kriging of residuals from linear regression between climatic data and elevation. The method provides good results in terms of accuracy in reproducing missing data for both the climatic dataset, as demonstrated in similar context (Di Piazza et al. 2015). The Turc modified method by Santoro (1970) was used to calculate the actual evapotranspiration term. Based on literature data and field measurements potential infiltration indexes were evaluated. Then, runoff was calculated as difference between effective precipitation and effective annual aquifer recharge. Results have shown that LTAAR for the whole hydrographic district of Sardinia ranges from 1600 (1971-2000) to 1540 (1981-2010) and 1690 (2009-2018) Mm3, representing 15% of the average annual precipitation; more than 65% of the annual available water is lost through evapotranspiration; the remaining 20% occurs as runoff.