China's huge ground-water and carbon footprint nexus revealed
Irrigation in China dates back more than 2,500 years and has been a major factor in supporting Chinese civilization and prosperity over the millennia. While the traditional system of dams, levees, canals and sluices continue to be used, it has been greatly augmented by ground water pumping in recent decades.
The impact of this on water tables is quite well known but new research has revealed that the practice also has a significant carbon footprint. A paper, published in Environmental Research Letters, estimates that the pumping systems that support China’s immense irrigation network produce 33.1 MtCO2e (33.1 mega tonnes of carbon dioxide equivalent) per year. This accounts for more than 0.5 percent of China’s total CO2 emissions and is similar to New Zealand’s annual emissions.
This research is the result of collaboration between institutes in China and the UK, including: the Chinese Academy of Agricultural Sciences, the Centre for Chinese Agricultural Policy, the University of East Anglia, the Tyndall Centre for Climate Change Research and Cranfield University.
China is now second only to India in tapping largely unreplenishable aquifers and, as a result, water tables in some of the worst affected areas are falling at the rate of more than two metres a year.
Groundwater used for crop irrigation in China has grown from 10 billion cubic metres in 1950 to more than 100 billion today. Roughly 70 percent of the irrigated area in northern China is groundwater-fed and studies show that pumping water for irrigation is one of the highest on-farm energy consuming processes. The CO2 emissions are large because it takes a great deal of energy to pump water from underground – in some areas from an average depth of 70 meters.
"Farmers are drilling more boreholes and pumping from ever deeper depths. There are already hotspots where this is unsustainable," said Declan Conway, of the Tyndall Centre for Climate Change Research, one of the paper’s lead authors. “The signals are that this must be turned around.”
Chinese food production depends fundamentally on water because of the extensive use of irrigation, with agriculture accounting for 62 percent of total freshwater use. The paper’s authors note, however, that the country faces its own “perfect storm” as rapid economic transition drives increasing per capita demand for water, food and energy with far-reaching environmental consequences. The pressure on water resources is now immense.
“Water scarcity in China is already driving policies to improve water conservation so it is crucial to identify water-energy trade-offs and potential co-benefits,” said Sabrina Rothausen from the University of East Anglia. “Our results suggest that an integrated policy approach could promote considerable water and energy savings.”
With a growing population, climate change and socio-economic transition, the report predicts the problem will worsen unless action is taken to improve China’s water management policies
“Improved access to pumping technology, cheap energy and the ability to directly control water availability has led to a massive expansion of groundwater pumping across large parts of Asia, particularly in China and India,” said Prof Jinxia Wang of the Centre for Chinese Agricultural Policy “The small scale of pump operations makes regulation and control of use extremely difficult.”
With a growing population and rising living standards, the demand for food in China, particularly animal products, is increasing. It is estimated that shifts in food consumption patterns and population growth may lead to additional unconstrained requirements of 407–515 km3 water for food production by 2030, compared with 2003.