The impact of climate change on groundwater temperature of the Piedmont Po plain (NW Italy): preliminary results

Abstract

It’s now recognized that a global climate change is taking place, leading to an increase in temperatures and a variation in precipitation regime, also affecting groundwater (GW) (Taylor et al., 2013). In this study we want to evaluate how climate change affects GW temperature in the Piedmont Po plain (NW Italy). The Piedmont Po plain covers the 27% of the whole region and it’s the most important GW reservoir of the Piedmont region (De Luca et al., 2020). It consists, from top to bottom, by Alluvial deposit complex (lower Pleistocene-Holocene), that hosts a shallow unconfined aquifer, the “Villafranchiano” transitional complex (late Pliocene-early Pleistocene), that hosts a multilayered aquifer, and a Marine complex (Pliocene) hosting a confined aquifer (De Luca et al., 2020). For this research, 41 wells in the shallow aquifer and 20 weather stations were selected throughout the Piedmont Po plain area, and GW and air temperature parameters were analysed for the period 2010-2019. The GW temperature data were firstly studied with basic statistical analysis (mean, maxima, minima) and then with the Mann-Kendall and Theil-Sen methods to evaluate the trend of the monthly mean GW temperatures. GW temperatures show a general increase in all the plain, up to a maximum of 2.18 °C/10 years. The same analyses were carried out for the air temperature data and it was observed that the increases vary between 1.52 and 2.11 °C/10 years. Then to compare water and air temperature, the Voronoi polygons method was used on QGis by centring the polygons on the weather stations. From this comparison, it was possible to highlight that in most cases (37 on 41, thus 90% of the analysed couples of temperature data) there is a greater increase in the monthly mean air temperatures than in the monthly mean GW temperatures. The same behaviour was observed for the monthly minima and maxima GW and air temperature. These results testify a greater resilience of GW temperature to climate variability. Future insights will be a detailed analysis of the factors influencing the more or less evident increase in GW temperatures in relation to air temperatures (e.g. depth of the water table, position of the monitoring well, position of the probe inside the well...).