Water balance of global aquifers revealed by groundwater footprint

Abstract

Groundwater is a life-sustaining resource that supplies water to billions of people, plays a central part in irrigated agriculture and influences the health of many ecosystems. Most assessments of global water resources have focused on surface water, but unsustainable depletion of groundwater has recently been documented on both regional and global scales. It remains unclear how the rate of global groundwater depletion compares to the rate of natural renewal and the supply needed to support ecosystems. Here we define the groundwater footprint (the area required to sustain groundwater use and groundwater-dependent ecosystem services) and show that humans are overexploiting groundwater in many large aquifers that are critical to agriculture, especially in Asia and North America. We estimate that the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers and that about 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat. That said, 80 per cent of aquifers have a groundwater footprint that is less than their area, meaning that the net global value is driven by a few heavily overexploited aquifers. The groundwater footprint is the first tool suitable for consistently evaluating the use, renewal and ecosystem requirements of groundwater at an aquifer scale. It can be combined with the water footprint and virtual water calculations, and be used to assess the potential for increasing agricultural yields with renewable groundwaterref. The method could be modified to evaluate other resources with renewal rates that are slow and spatially heterogeneous, such as fisheries, forestry or soil.

Selection of spatial scale for assessing impacts of groundwater-based water supply on freshwater resources

“…In their study of the world's regional groundwater aquifers, Gleeson et al (2012) found that the regional aquifer covering Jylland had a degree of water stress equivalent to a WSI of 0.44, which is 83% higher than our WSI calculations based on RBMP data. On the other hand, Gleeson et al (2012) found that the regional aquifer covering Sjaelland had a WSI of 0.86, which is 38% less than our results indicate.…”

“…In their study of the world's regional groundwater aquifers, Gleeson et al (2012) found that the regional aquifer covering Jylland had a degree of water stress equivalent to a WSI of 0.44, which is 83% higher than our WSI calculations based on RBMP data. On the other hand, Gleeson et al (2012) found that the regional aquifer covering Sjaelland had a WSI of 0.86, which is 38% less than our results indicate. Even larger differences are found when comparing our results with those from a study of the freshwater resources of the world by Smakhtin et al (2004), who found that Scandinavia (as a whole) had no water stress (WSI < 0.3).…”

“…It has been estimated that 20% of the World's major aquifers are being mined at an unsustainable rate (Gleeson et al, 2012) and with major aquifers depleting by up to 40 mm/yr, there are calls for increased appreciation of groundwater's special role in the provision of water for human and environmental needs (Famiglietti, 2014).…”

Comparing potential recharge estimates from three Land Surface Models across the western US

“…Groundwater is a life-sustaining natural resource that supplies water to billions of people on earth (Gleeson et al, 2012). It plays a central part in irrigated agriculture and sustaining ecosystems (Giordano, 2009;Siebert et al, 2010), and enables human adaptation to climate variability and change (Taylor et al, 2013).…”

“…Spatial variability of recharge rates is controlled by precipitation and other climate variables Gleeson et al, 2012), vegetation, soils, and geology (Stonestrom et al, 2007). Despite the importance of groundwater in this region, limited recharge estimates are available due to the complexity of recharge processes and the lack of feasible measurement methods (Scanlon et al, 2006).…”