China’s groundwater irrigation system is responsible for polluting the atmosphere with more than 30 million tonnes of CO₂ per year – according to research from the University of East Anglia.

Groundwater used for crop irrigation in China has grown from 10 billion cubic metres in 1950 to more than 100 billion today.

A research paper, published  in Environmental Research Letters, estimates that the pumping systems which support this immense irrigation network annually produce 33.1 MtCO₂e (33.1 mega tonnes of carbon dioxide equivalent).

China is the largest greenhouse gas emitter in the world, with around 17 per cent of emissions coming from agriculture. Irrigated agriculture in China produces 70 per cent of the country’s grain. But it takes some 500 litres of water to grow the wheat for one small loaf of bread.

Pollution is caused by the huge amount of energy needed to pump water from underground – in some areas from an average depth of 70 meters. This research is the first to calculate how much pollution is being created.

It is the result of a collaboration between the university’s School of International Development, the UEA Water Security Research Centre and the UEA-based Tyndall Centre for Climate Change Research, with the Centre for Chinese Agricultural Policy and the Chinese Academy of Agricultural Sciences in Beijing, and Cranfield University.

The research team used extensive survey data collected from 366 villages in 11 provinces. They up-scaled these results to calculate the emissions created by groundwater pumping across China’s remaining 20 provinces.

The results account for more than 0.5 per cent of China’s total CO₂ emissions. For comparison, this is similar to the total amount of CO₂ that the whole of New Zealand emits in one year.

Prof WANG Jinxia of the Centre for Chinese Agricultural Policy，Institute of Geographic Sciences and Natural Resources Research  said: “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. The small scale of pump operations makes regulation and control of use extremely difficult.”

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.

J. Wang, S.G.S.A Rothausen, D. Conway, L. Zhang, W. Xiong, I.P. Holman and Y. Li (2012). China’s water-energy nexus: greenhouse-gas emissions from groundwater use for agriculture. Environmental Research Letters 7 014035 (http://stacks.iop.org/1748-9326/7/014035)