The exploitation of the middle Valseriana springs (northern Italy): current situation, studies undertaken, and next challenges

Approximately a quarter of the world population depends on the karst aquifers. Due to their significant storage capacity, high flow rate, and reduced cost of extraction, they are a strategic resource in areas where water demand is intense (e.g., in big cities, tourist sites, and farmlands). In this context, a hydrogeological characterization of the water resource is crucial for developing an aware and sustainable management. Therefore, qualitative-quantitative monitoring aimed at obtaining all data for a comprehensive analysis of the resource, its variations over time, and the possible developments under climate change is required. Nossana represents one of the most important springs in northern Italy in terms of discharges and impact, supplying the drinking needs of more than 300,000 people in the Bergamo metropolitan area. In the 2018-2019, the joint effort between the water company and the Università degli Studi di Milano carried out a monitoring campaign on about 30 springs in the middle Valseriana for the characterization of the area. As part of a broad understanding of the hydrogeological dynamics, several outputs have been produced in the years following the monitoring. In order to assess the vulnerability of karst aquifers, a new index-based approach was developed by considering the distance between major discontinuities and the main spring as an innovative element. This technique has highlighted the most vulnerable zones and it could also help in redefining the spring protection areas. In coupling with physical-chemical analyses, the resident time of some springs was estimated by 3H/3He isotopic method and compared with previous results to have an insight into the evolution and renewal of the water resource. Faint aging was noted for the Nossana (1-2 years), which needs to be further investigated in future years to understand whether it is a temporary condition or the beginning of an established behavior. Furthermore, a rainfall-runoff model of the Nossana spring was implemented, calibrated, and 3 different IPCC climate change scenarios were simulated using the downscaled data obtained from a Regional Climate Model ensemble. The predicted mean discharges are lower than observations (3%-23%) for all scenarios considered, although a clear trend is not detected. After 2060, an increase in the duration of periods with discharges below warning thresholds is expected consistent with the precipitation trend, characterized by long and dry summers and wetter autumns compared to the current climate. The use of these tools and analyses repeated at intervals over time can contribute to improved management and more conscious planning of spring water use or, alternatively, drive the search for alternative resources. This in-depth characterization approach has been focused mainly on the most important springs in the area (e.g., Nossana) but is still ongoing by attempting to expand knowledge on the potential of all spring water resources in the Bergamo Pre-Alps.