Analysis of groundwater drought in the Piemonte region using standardized indices

Groundwater drought is a condition of prolonged decrease in groundwater levels respect to normal conditions. This phenomenon is increasing the concern about the impact of climate change and growing water demands in recent years. The objective of this study is to analyze the connection between meteorological drought and groundwater drought, in the Piemonte Plain. Aquifers of this area are largely influenced by water withdrawals for agriculture and irrigation. The monitoring network of Regione Piemonte and the gridded data of Arpa Piemonte are used to characterize the piezometric levels and precipitation respectively, enabling the analysis of both spatial and temporal dimensions. As a first step, the trend analysis of piezometric level is carried out. The analysis shows positive trends in the North-East of Piemonte and in the area near and South of Torino. Strong negative trends are present in the center of the region, at the North of the Po river. Results compare well and improve a previous report of Regione Piemonte dated 2017 The scientific literature points out an attenuation and delay of groundwater drought in response to a meteorological drought. This study investigates this aspect using two standardized indices: the Standardized Precipitation Index (SPI) and the Standardized Groundwater Index (SGI) over various time windows. A strong correlation between SGI and SPI indices at larger time windows (6 to 12 months) are observed. Due to the intensive cultivation and irrigation practices in the Piemonte Plain, the comparison is carried out separately for the summer (April-September) and winter (October-March) periods, revealing substantial differences in the correlation between the two indices. These differences may be attributed to water abstraction for agricultural purposes. Additionally, an analysis of lag response explores how the groundwater system reacts to the meteorological drought and the delay at which this response occurs. Results indicate an heterogeneous behaviour, although no clear spatial pattern of lag propagation can be identified. Overall, this research provides valuable insights into the relationship between meteorological drought and groundwater drought, in a region highly affected by water abstraction and irrigation. The findings offer a starting point for groundwater drought analysis in Piemonte Plain. Knowledge of the interaction between meteorological and groundwater drought is essential for an effective water resource management due the future increasing water demands and changes of climatic conditions.