Editorial: Groundwater systems worldwide

Groundwater, with a total volume of 23.4 × 10 km, represents 30% of the world’s freshwater or 2.5% of the total global water storage. Thus, it is an important area of research and a valuable resource for humankind (Oki and Kanae, 2006). Groundwater is an essential component of the global hydrological and biogeochemical cycles and plays a major role in ecosystems sustainability (Zektser and Loaiciga, 1993; Jackson et al., 2001; Sophocleous, 2002; Griebler and Avramov, 2015; Frappart et al., 2019). Similarly, groundwater is an essential water resource for meeting various human needs, including domestic water supply, irrigation and industrial operations. Groundwater is often the last freshwater resource available for domestic use and irrigation once surface waters are depleted, especially in semi-arid areas and densely populated countries (Giordano, 2009; Siebert et al., 2010). In many regions of the world, aquifers are the largest and safest drinking water supply (Doveri et al., 2015). Groundwater storage and flows are increasingly affected by human activities (Zektser and Everett, 2004; Shah, 2007) and climatic stresses (Döll, 2009; Green et al., 2011; Taylor et al., 2013). This may have negative consequences both for the functioning of the terrestrial environment and ecosystems as well as water supply for large populations due to the depletion of groundwater levels in many regions around the world. A depletion of 4,500 km was estimated worldwide between 1900 and 2008 (Konikow, 2011). Despite this global groundwater crisis (Famiglietti, 2014), groundwater is either poorly monitored or not monitored in many regions of the world (Jones, 2011). Thus, there is an urgent need to understand the properties and behaviour of groundwater systems around the world to support sustainable water resources managment. The authors in this Research Topic provided original contributions on two broader topics: i) modelling and mapping of groundwater systems; and ii) impact of natural and anthropogenic stresses on groundwater supply. Kaewdum and Chotpantarat analyzed groundwater recharge potential in the lower Khwae Hanuman sub-basin in Thailand based on geological and hydrogeological features. This region anually faces water shortage during the dry season and groundwater is used as an additional freshwater source, especially for irrigation purposes. Using a weighted OPEN ACCESS