Assessment of transboundary aquifers of the worldvulnerability arising from human water
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2013 Environ. Res. Lett. 8 024003
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IOP PUBLISHING ENVIRONMENTAL RESEARCH LETTERS
Environ. Res. Lett. 8 (2013) 024003 (13pp) doi:10.1088/1748-9326/8/2/024003
Assessment of transboundary aquifers ofthe worldvulnerability arising fromhuman water useYoshihide Wada1 and Lena Heinrich2
1 Department of Physical Geography, Faculty of Geosciences, Utrecht University, Heidelberglaan 2,3584 CS Utrecht, The Netherlands2 International Groundwater Resources Assessment Centre, Westvest 7, 2611 AX Delft, The Netherlands
E-mail: [email protected]
Received 20 December 2012Accepted for publication 18 March 2013Published 4 April 2013Online at stacks.iop.org/ERL/8/024003
AbstractInternationally shared, or transboundary, aquifers (TBAs) have long played an important rolein sustaining drinking water supply and food production, supporting livelihoods of millions ofpeople worldwide. Rapidly growing populations and their food demands cast significant doubton the sustainability of TBAs. Here, this study provides a first quantitative assessment ofTBAs worldwide with an aquifer stress indicator over the period 19602010 usinggroundwater abstraction, groundwater recharge, and groundwater contribution to environmentflow. The results reveal that 8% of TBAs worldwide are currently stressed due to humanoverexploitation. Over these TBAs the rate of groundwater pumping increased substantiallyduring the past fifty years, which worsened the aquifer stress condition. In addition, manyTBAs over Europe, Asia and Africa are not currently stressed, but their aquifer stress has beenincreasing at an alarming rate (>100%) for the past fifty years, due to the increasing relianceon groundwater abstraction for food production. Groundwater depletion is substantial overseveral TBAs including the India River Plain (India, Pakistan), the Paleogene and Cretaceousaquifers (the Arabian Peninsula), and a few TBAs over the USAMexico border. Improvingirrigation efficiency can reduce the amount of groundwater depletion over some TBAs, but itlikely aggravates groundwater depletion over TBAs where conjunctive use of surface waterand groundwater is prevalent.
Keywords: transboundary aquifers, aquifer stress, groundwater recharge, groundwaterabstraction, groundwater depletion, irrigation
S Online supplementary data available from stacks.iop.org/ERL/8/024003/mmedia
Internationally shared, or transboundary, groundwater re-sources have long played an important role in sustaininghuman water needs, e.g. agriculture and other uses, and
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natural ecosystems (Bittinger 1972, Margat 1985, Hayton andUtton 1989, Foster and Chilton 2003, Puri and Aureli 2005,Llamas and Martnez-Santos 2005, Ahmad et al 2005, Davieset al 2013). Yet, they have received significantly less attentioncompared to transboundary river basins (Puri 2001, Ecksteinand Eckstein 2005, Puri and Aureli 2005) that have beenextensively studied worldwide since the first compilation ofthe Register of International Rivers in 1978 (United Nations1978, Wolf et al 1999). In 2000, Internationally SharedAquifer Resources Management (ISARM) was established
11748-9326/13/024003+13$33.00 c 2013 IOP Publishing Ltd Printed in the UK
Environ. Res. Lett. 8 (2013) 024003 Y Wada and L Heinrich
at the 14th Session of the Intergovernmental Council ofthe International Hydrological Programme of UNESCO.Since then, substantial efforts have been made to identifytransboundary aquifer or aquifer systems in various regions,e.g. Africa, Europe, the Americas, and to raise awarenessof their societal and environmental importance (Eckstein andEckstein 2005, Puri and Aureli 2005, Davies et al 2013).
Transboundary aquifers (TBAs) traverse internationalpolitical boundaries, such that groundwater transfers fromone country to the others. For instance, most of thegroundwater recharge may occur in one country, whereasthe groundwater may be extensively abstracted in the othercountries. Given the complex nature, TBAs can be classifiedinto different types. Eckstein and Eckstein (2005) definedsix different types of TBAs according to the hydrogeologicalconditions, e.g. physical boundary, (un)confined condition,and hydraulic connectivity with surface water bodies suchas river, lakes and wetlands. Davies et al (2013) highlightedthe importance of socio-economic factors (e.g., waterdemand, land use, human activities), environmental issues(e.g., sustainability) and institutional elements (e.g., thedegree of cooperation, governance capability) together withthe hydrological conditions.
Despite the significance, few quantitative assessmentsof TBA(s) are present. Cobbing et al (2008) analyzed thegroundwater resources availability and the correspondingwater demand over a few TBAs shared by South Africa andthe neighboring countries. Regional studies by Rodell et al(2009) and Tiwari et al (2009), using the Gravity Recoveryand Climate Experiment (GRACE), revealed a considerableamount of groundwater depletion, i.e. the persistent removalof groundwater from aquifer storage owing to groundwaterabstraction in excess of groundwater recharge, from theaquifer underlying India, Pakistan, and Bangladesh, most ofwhich is used for irrigation for food production. A recentstudy by Gleeson et al (2012) calculated the groundwaterfootprint, i.e. the area required to sustain groundwaterabstraction and groundwater-dependent ecosystem services,for major groundwater basins (BGR/UNESCO 2008). Thesestudies suggest that some TBAs are under substantial stress,yet no comprehensive overview of aquifer stress of globalTBAs is available.
Here, a first quantitative assessment of TBAs is providedworldwide with an aquifer stress indicator over the period19602010 that extends beyond most global analyses. Theaquifer stress indicator (AQSI) is calculated with groundwaterabstraction (GWA), natural groundwater recharge (RNat), andadditional recharge from irrigation as return flow (RIrr).In addition, groundwater contribution to environment flow(REnv) is incorporated. In many regions, groundwater providesa reliable source of water to environment, such as baseflow instreamflow. This term, thus, encompasses the broad meaningof environmental significance of groundwater recharge,not only sustaining groundwater-dependent ecosystems instreamflow, wetlands, springs, and marine environments,but also contributing to evapotranspiration from vegetation,e.g. forest. The AQSI is defined as GWA/[(RNat+RIrr)REnv](all in volume per time such as km3 yr1) that essentially
expresses how much fraction of the available groundwaterrecharge is used for human water use. The AQSI used a similarconcept as groundwater footprint (GF) developed by Gleesonet al (2012), but it is expressed as a dimensionless unit ratherthan area (AA; m2), thus equals to GF/AA. The AQSI above1 is possible at the expense of groundwater contribution toenvironmental flow and groundwater mining or groundwaterdepletion. It should be noted that to estimate the amount ofgroundwater depletion, the difference between abstraction andrecharge or GWA(RNat+RIrr) is used, which approximatelyexpresses the change in aquifer storage. The fluxes over eachTBA is aggregated to calculate the AQSI and the amount ofgroundwater depletion, integrating lateral groundwater flowthat may naturally occur due to the difference in groundwaterheads and might occur due to groundwater pumping. Inthis study, the term aquifer refers solely to groundwaterresources and the term TBAs refer to groundwater resourcesthat traverse international political boundaries among multiplecountries.
In section 2, the data, model and methods used aredescribed. The results are presented in section 3 and insection 4 the discussion is presented and the conclusions aredrawn.
2. Data, model and methods
2.1. Transboundary Aquifers of the World
A global inventory of TBAs was obtained from Trans-boundary Aquifers of the WorldUpdate 2012 (www.un-igrac.org/publications/456/) compiled by the Interna-tional Groundwater Resources Assessment Centre (IGRAC;www.un-igrac.org/). Transboundary Aquifers of the WorldUpdate 2012 provides, to our knowledge, the first spatiallyexplicit and the most comprehensive information on TBAsworldwide. At present, it identifies 445 TBAs and delineatesaquifer boundaries. The number of TBAs was 380 in2009 (Transboundary Aquifers of the World 2009; www.un-igrac.org/publications/323/), but substantially increased asa result of various international efforts identifying TB
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