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WATER RESOURCES RESEARCH, VOL. 43, W03437, doi:10.1029/2006WR005486, 2007

Global impacts of conversions from natural to agricultural ecosystems on water resources: Quantity versus quality

Bridget R. Scanlon

Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas, USA


Ian Jolly

CSIRO Land and Water, Adelaide, South Australia, Australia


Marios Sophocleous

Kansas Geological Survey, Lawrence, Kansas, USA


Lu Zhang

CSIRO Land and Water, Canberra, ACT, Australia


Abstract

Past land use changes have greatly impacted global water resources, with often opposing effects on water quantity and quality. Increases in rain-fed cropland (460%) and pastureland (560%) during the past 300 years from forest and grasslands decreased evapotranspiration and increased recharge (two orders of magnitude) and streamflow (one order of magnitude). However, increased water quantity degraded water quality by mobilization of salts, salinization caused by shallow water tables, and fertilizer leaching into underlying aquifers that discharge to streams. Since the 1950s, irrigated agriculture has expanded globally by 174%, accounting for ∼90% of global freshwater consumption. Irrigation based on surface water reduced streamflow and raised water tables resulting in waterlogging in many areas (China, India, and United States). Marked increases in groundwater-fed irrigation in the last few decades in these areas has lowered water tables (≤1 m/yr) and reduced streamflow. Degradation of water quality in irrigated areas has resulted from processes similar to those in rain-fed agriculture: salt mobilization, salinization in waterlogged areas, and fertilizer leaching. Strategies for remediating water resource problems related to agriculture often have opposing effects on water quantity and quality. Long time lags (decades to centuries) between land use changes and system response (e.g., recharge, streamflow, and water quality), particularly in semiarid regions, mean that the full impact of land use changes has not been realized in many areas and remediation to reverse impacts will also take a long time. Future land use changes should consider potential impacts on water resources, particularly trade-offs between water, salt, and nutrient balances, to develop sustainable water resources to meet human and ecosystem needs.

Received 31 August 2006; accepted 3 November 2006; published 27 March 2007.

Keywords: irrigation; land cover change; rain-fed agriculture.

Index Terms: 1632 Global Change: Land cover change; 1813 Hydrology: Eco-hydrology; 1842 Hydrology: Irrigation; 1884 Hydrology: Water supply.

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Citation: Scanlon, B. R., I. Jolly, M. Sophocleous, and L. Zhang (2007), Global impacts of conversions from natural to agricultural ecosystems on water resources: Quantity versus quality, Water Resour. Res., 43, W03437, doi:10.1029/2006WR005486.