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Title: The use and re-use of unsustainable groundwater for irrigation: A global budget

Depletion of groundwater aquifers across the globe has become a significant concern, as groundwater is an important and often unsustainable source of irrigation water. Simultaneously, the field of water resource management has seen a lively debate over the concepts and metrics used to assess the downstream re-use of agricultural runoff, with most studies focusing on surface water balances. Here, we bring these two lines of research together, recognizing that depletion of aquifers leads to large amounts of groundwater entering surface water storages and flows by way of agricultural runoff. While it is clear that groundwater users will be impacted by reductions in groundwater availability, there is a major gap in our understanding of potential impacts downstream of groundwater pumping locations. We find that the volume of unsustainable groundwater that is re-used for irrigation following runoff from agricultural systems is nearly as large as the volume initially extracted from reservoirs for irrigation. Basins in which the volume of irrigation water re-used is equal to or greater than the volume of water initially used (which is possible due to multiple re-use of the same water) contain 33 million hectares of irrigated land and are home to 1.3 billion people. Some studies havemore » called for increasing irrigation efficiency as a solution to water shortages. We find that with 100% irrigation efficiency, global demand for unsustainable groundwater is reduced by 52%, but not eliminated. In many basins, increased irrigation efficiency leads to significantly decreased river low flows; increasing irrigation efficiency to 70% globally decreases total surface water supplies by ~600 km 3 yr –1. Lastly, these findings illustrate that estimates of aquifer depletion alone underestimate the importance of unsustainable groundwater to sustaining surface water systems and irrigated agriculture.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1]
  1. Univ. of New Hampshire, Durham, NH (United States)
  2. Univ. of New Hampshire, Durham, NH (United States); Zentrum fur Entwicklungsforschung, Bonn (Germany)
Publication Date:
Grant/Contract Number:
SC0005171
Type:
Published Article
Journal Name:
Environmental Research Letters
Additional Journal Information:
Journal Volume: 12; Journal Issue: 3; Journal ID: ISSN 1748-9326
Publisher:
IOP Publishing
Research Org:
Univ. of New Hampshire, Durham, NH (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; water-use; surface-water; efficiency; productivity; depletion; stress; hydrology; agriculture; austainability; water re-use
OSTI Identifier:
1346266
Alternate Identifier(s):
OSTI ID: 1355931