Francesco Maria De Filippi

Both groundwater and surface water are essential sources of freshwater worldwide. In urban and peri-urban areas of Sub-Saharan Africa, such as Dar es Salaam city (Tanzania), the scarcity of good quality surface water has led to a groundwater overexploitation in the coastal aquifer. This is due to the growing water demand driven by demographic and economic development of the city. The rapid and uncontrolled urban expansion, together with the increase of impermeable areas, have negative impacts on the aquifer recharge, water table decrease and runoff increase, causing higher risk of flooding, erosion and water shortage. This paper presents the separate assessments of land use land cover change (LULCC) and climate variability impacts on water budget in the study area, using remote sensing datasets, which have followed the evolution of Dar Es Salaam City during the period 2002-2022. The assessments show how rapid urbanization has increased runoff and reduced aquifer recharge, leading to flooding risks and groundwater degradation. In 20 years, within the hydrogeological basin, the aquifer lost 30% of the recharge water volume, on average. Climate variability has affected the specific annual recharge and runoff volumes, especially in the last decade, due to an important rainfall increase. This paper demonstrates that combining the analysis of LULCC and climate variability in catchment areas with geomorphological ones and hydrogeological water budget method can provide a thorough understanding of uncontrolled urban spread effects on water resources balance and support evidence based decision-making spatial planning and environmental management. The study is part of the WECOAdapt project (Water management through ECOhydrology for climate change ADAPTation) that focuses on the reduction of negative impacts on floods and droughts due to unsustainable urban development, aiming to reverse/reduce the degradation of water and land resources.

Aquifers and karst springs are among the most studied and challenging topics of hydrogeology in recent years. They are difficult to model due to the aquifer's heterogeneity and anisotropy, as well as the difficulties of conventional monitoring. However, they are among the most important groundwater resources, accounting for a significant portion of freshwater intended for human consumption, especially in the EU.The study area is located in the Umbria Region in central Italy and is characterised by an elongated carbonate ridge formed by a multilayered karstified carbonate succession, locally separated by marly interbeds. Groundwater circulation is controlled by Apennine tectonics, with faults either enhancing or limiting hydraulic connectivity between hydrogeological units. Recharge occurs predominantly through diffuse but also local infiltration over carbonate outcrops and high plains.This study contributes to the understanding of hydrogeological functioning by integrating long-term monitoring data (more than 20 years) of discharge and rainfall with numerical modelling.The data reveal that the karst system exhibits highly complex hydrological behaviour, and the distinctive hydrograph shapes observed for certain springs are attributed to direct surface water inputs entering the system through local sinkholes. Modkarst Model that was applied to six major karst springs, allowed the quantification of surface water contribution.This work highlights that effective management of karst aquifers under increasing climate change effects that usually requires integrated approaches combining geological understanding, continuous monitoring, and modelling.

Groundwater sampling is a critical component of hydrogeological investigations and is essential for accurate hydrogeochemical analyses. Fully representative samples can be obtained after effective purging of non-representative stagnant water from monitoring wells. However, the procedure and threshold for sufficient well purge remain unresolved. In practice, wells are often purged from 5 to 60 minutes according to the stabilization of chemical-physical parameters or 3–5 well volumes without a rigorous scientific basis, after which samples are collected under the assumption that they represent formation conditions. This introduces substantial uncertainty and potential errors into sampling data.To address this issue, we develop a well storage-mixing model to characterize the combined effects of two key processes during purging: well storage depletion and wellbore mixing. By modeling the dimensionless completion variables of these two processes, ηq [-] and ηc [-], we demonstrate that sufficient well purge is controlled by the process with the longer characteristic timescale. In high-yield aquifers or large, deep wells, wellbore mixing limits the time required to achieve sufficient purging; conversely, in low-yield aquifers or shallow, small wells, storage depletion is the limiting process. Field data from recent sampling campaigns in Rome, Italy, and Inner Mongolia, China, exhibit mixing-limited and storage-limited purge modes, respectively, indicating that different well geometries and hydrogeological settings lead to distinct purge times and volumes. Accordingly, purge criteria should be dynamic to avoid over-purging (unnecessary capital costs) or insufficient purging (non-representative samples). Dynamic purging informed by the storage-mixing model significantly improves data accuracy while reducing capital costs and should be widely adopted, particularly for monitoring well networks with highly variable well geometries and aquifer conditions.

The Farfa River is one of the most important tributaries on the left bank of the Tiber River, upstream Rome in Central Italy. Its water has a very high quality and a geochemical composition mainly associated with the calcium-bicarbonate facies, primarily due to the overflow of the Capore karst Spring, which is one of the main two spring supplying the city of Rome. In the final stretch toward the confluence with the Tiber River these geochemical characteristics completely change and according to the Regional Environmental Protection Agency's classification the river water quality status degrades from good to sufficient, suggesting that this may be due to potential pollution or contamination by human-related activities. This new study, using discharge and physico-chemical field measurements over four monitoring campaigns, together with the help of geochemical and multi-isotopic tracers (C, S, O, H) analyzed on water samples collected, reveals that this change is actually natural and related to the river's interaction with a group of springs, whose origin and recharge areas were largely unknown until now. The use of specific isotopes, such as 13C/12C and 34S/32S, has allowed to better understand the groundwater flowpaths, recharge areas and potential interactions with deep fluids upwelling along fault planes present in the study area.

The Island of Unguja in Zanzibar (Tanzania) has experienced an accelerated urban development growth since the 1990s due to a rapidly increasing population. These rapid land demands put additional stress on the country’s ability to plan urban centers, cities, and the management of natural resources. The study aimed to determine the impact of urbanization on groundwater availability in the catchment area of the Masingini–Mwanyanya forest reserves from 1992 to 2022. The study used a detection approach to determine the Land Use Land Cover (LULC) changes for three decades, starting from 1992 to 2022. Landsat remote sensed images of 1992, 2002, 2012, and 2022 were used. Additionally, a paired t-test was conducted to determine the significant changes in mean population growth, urbanization, and humidity. The aquifer recharge evolution analysis was conducted using the QGIS software (3.34.8 released version). Obtained results revealed that for these three decades, the forest areas decreased by 14.5% (i.e., from 8.3 km² in 1992 to 7.1 km² in 2022), while built-up area increased from 0 km² in 1992 to 1.7 km² in 2022. Moreover, the evolution of undesirable Land Use Land Cover (LULC) changes, particularly the persistent conversion of forested areas into built-up zones, has been detected. This trend poses a significant threat to the sustainable management of water resources and catchment forest reserves. The study also indicated a decline in the recharge of the coastal aquifer supplying Zanzibar City, which decreased from 15.5 Mm³ to 11.1 Mm³. These findings highlight that the Masingini Forest Reserve is increasingly encroached by rapid urbanization, which is a phenomenon that may jeopardize the availability and sustainability of groundwater resources in the catchment without proper urban planning. Based on these results, the study recommends further research and upscaling of the existing findings, as well as collaboration with relevant authorities to redefine the Masingini–Mwanyanya forest catchment area to ensure the sustainable use of groundwater resources.

Groundwater is an essential source of freshwater worldwide. In urban and peri-urban areas of Sub-Saharan Africa cities, such as Dar es Salaam (Tanzania), the scarcity of good quality surface water has led to the overexploitation of the aquifer, due to the growing demand for water linked to the demographic and economic development of the city. This has also caused the phenomenon of saltwater intrusion degrading the quality of groundwater resources. In addition, rapid urban expansion and the consequent increase in impermeable areas, hindering infiltration, have led to a reduction in groundwater recharge with significant water table decrease. This study explores the potential of managed aquifer recharge (MAR) as a sustainable solution for integrated water resource management by assessing their suitability in selected areas of Dar es Salaam City. The infiltration process has been modelled with SEEP-W software, considering different basins with embankments and two scenarios: a constant head water volume given by a flooding event and a high intensity precipitation event inducing the storage of rainfall water. The results show that MAR can represent a useful tool for integrated water resource management in the study area with the potential to effectively enhance groundwater sustainability and contributing to more resilient urban water systems in the city.

The construction of underground infrastructure in urban environments can significantly alter groundwater flow dynamics, particularly in karst settings, which are characterized by high permeability, rapid groundwater flow, and strong spatial variability in recharge and discharge processes. Tunneling in a karst system can severely deplete an aquifer and undermine the sustainability of water resources over the long term. These impacts pose significant challenges for regional water resources management, highlighting the urgent need for strategies that support both sustainable development and the protection of these complex hydrogeological systems. One of the most critical consequences of such construction activities can be tunnel drainage, which can modify the hydrogeological balance of karst aquifers. For this reason, an accurate estimation of groundwater recharge remains a major challenge, yet it is essential for effective groundwater management, particularly in regions that rely heavily on karst groundwater resources. This paper proposes a GIS-based methodological framework to assess the active recharge of the karst aquifer feeding the Mazzoccolo Spring, located in the urban area of Formia (southern Latium Region, Central Italy), which is potentially affected by a planned underground infrastructure. The study focuses on delineating the recharge area and evaluating the potential impacts of tunneling on this complex and sensitive hydrogeological system.

Karst hydrogeology is the branch of hydrogeology that studies how groundwater flows and behaves in karst systems, characterized by the presence of soluble rocks (mainly limestone and dolomite) that favour chemical dissolution by meteoric water

The water framework directive (WFD) addressed by the EU raises specific questions on the ecological flow of rivers, requiring a quantitative and qualitative assessment related to ungauged water resources. The Farfa River is one of the most important tributaries on the left bank of Tiber River, upstream Rome in Central Italy. The final part of its course, downstream Granica, is part of the Nazzano-Tevere-Farfa Regional Nature Reserve, a ZPS zone (IT6020018 and IT6030012) and part of EU Natura 2000 network. This part is also the most interesting but at the same time the least studied in terms of hydrogeology and hydrology, characterized by a marked heterogeneity, important artificial modifications along the river and a strong groundwater - surface water interaction. A first quantitative evaluation is the main goal of this study, with discharge measurements carried out in specific sections chosen along the river course, allowing to assess springs’ contribution and human impacts to the Farfa River baseflow.