**Preface to "Advances in Urban Groundwater and Sustainable Water Resources Management and Planning"**

Water is a vital resource for the sustainable development and survival of humanity and ecosystems alike. The occurrence of this natural resource has always enabled the distribution of populations and biodiversity. In fact, early communities sought the proximity of springs, water courses, lakes, and rivers to establish settlements.

In nature, urban groundwater results in several processes, including climatic, geological, geomorphological, geochemical, ecotoxicological, and hydraulic processes, as well inducing sanitation. Urban development deeply impacts hydrological systems, particularly in the invisible component of the water cycle, the groundwater.

Urban and peri-urban areas continue to develop and expand uninterrupted, and urbanisation's extensive impact on groundwater is and associated with climate change and water quality degradation. The horizontal development of municipalities through urban expansion is a reality. In addition, the expansion in the underground environment must be considered, since this is the location of the infrastructures which relate to urbanisation and which have a significant impact on underground network areas (e.g., water supply, sewage, stormwater, metro, tunnels, and storage). Therefore, urban planning must consider the site's natural conditions (e.g., geology, geomorphology, groundwater, ecosystems) and the entire network of constructed infrastructure and underground structures.

This Special Issue emphasises the presentation and discussion of key studies on model urban and peri-urban areas. In addition, several papers describe the current state of the art on the challenges and emerging fields related to the mapping, characterisation, assessment, mitigation, and protection of sustainable groundwater systems and water resources in urban and peri-urban areas. In the current year, 2022, World Water Day has been committed to groundwater and the process making the invisible visible. Therefore, this Special Issue presents a set of papers that stimulate reflections, methodologies, and learned studies on the significance of fresh water in urban areas.

> **Helder I. Chamin ´e, Maria Jos´e Afonso, and Maurizio Barbieri** *Editors*
