Assessing the long-term sustainability of the groundwater resources in the Bacchiglione basin (Veneto, Italy) with the Mann–Kendall test:suggestions for higher reliability

Abstract

The social, economic, and ecological importance of the aquifer system within the Bacchiglione basin (Veneto, IT) is noteworthy,and there is considerable disagreement among previous studies over itssustainable use. Investigating the long-term quantitative sustainabilityof the groundwater system, this study presents a statistical methodologythat can be applied to similar cases. Using a combination of robust andwidely used techniques, we apply the seasonal Mann–Kendall test andthe Sen’s slope estimator to the recorded groundwater level timeseries.The analysis is carried out on a large and heterogeneous proprietarydataset gathering hourly groundwater level timeseries at 79 controlpoints, acquired during the period 2005–2019. The test identifiessignificant decreasing trends for most of the available records, unlikeprevious studies on the quantitative status of the same resource whichcovered the domain investigated here for a slightly different period:2000–2014. The present study questions the reason for such divergingresults by focusing on the method’s accuracy. After carrying out a Fourieranalysis on the longest available timeseries, for studies of groundwaterstatus assessment this work suggests applying the Mann–Kendall test totimeseries longer than 20 years (because otherwise the analysis wouldbe affected by interannual periodicities of the water cycle). A furtheranalysis of two 60-year-long monthly timeseries between 1960 and2020 supports the actual sustainable use of the groundwater resource,the past deployment of the groundwater resources notwithstanding.Results thus prove more reliable, and meaningful inferences on the longtermsustainability of the groundwater system are possible