How much water do we really taken from nature? New footprint separates consumption from appropriation

Water footprints estimate how much water is required to produce food, timber and other goods. But does every drop used by a crop represent water taken from nature? A study from south-central Chile suggests that conventional accounting may blur the difference between water consumption and human appropriation.

Published in International Soil and Water Conservation Research, the study introduces a revised water footprint that considers what would have happened if farmland or plantations had remained under natural vegetation. The proposed measure is intended to complement conventional water footprints. By connecting water accounting with land-use change, it could support more targeted irrigation policy, forestry planning and evaluation of the hidden water pressures associated with global trade.

Water footprints distinguish between blue water, drawn from rivers or groundwater for irrigation, and green water, rainfall stored in soil and used by plants. Traditional methods count nearly all rainwater consumed by crops in their green water footprint. The new approach counts only the additional rainwater use caused by land conversion, the portion that might otherwise have contributed to runoff or groundwater recharge.

“Rainfall would still be used by vegetation without agriculture or forestry,” says corresponding author Patricio Neumann-Langdon from Universidad Del Bío-Bío, Chile. “Our approach asks how much human land use actually changes natural water flows, rather than counting all water passing through crops.”

The researchers applied the method to agriculture and forestry across 149 municipalities in five regions of south-central Chile. They estimated annual human water appropriation at about 5 billion m³, which is 2.7 times lower than the conventional estimate. The revised green water estimate was 5.3 times lower.

“Agricultural appropriation was dominated by irrigation, particularly in drier farming areas,” says Neumann-Langdon. “Forestry plantations were the main source of rainwater appropriation because pine and eucalyptus can reduce the runoff that would occur under native vegetation.”

The researchers also examined virtual water, the water embodied in traded products. Almost 45% of the water appropriated in the study area was associated with exported agricultural and forestry goods, with China and the United States among the leading destinations. This links demand for fruit, wine, timber and pulp to changes in local water availability.

“A clearer distinction between consumption and appropriation can help decision-makers identify the water use that can actually be managed,” Neumann-Langdon adds.

Contact the author:

Patricio Neumann-Langdon

Global Change Research Group (CG-Lab). Department of Basic Sciences, Faculty of Sciences, Universidad del Bío-Bío, Chile.

pneumann@ubiobio.cl

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