The increasing effects in energy and GHG emission caused by groundwater level declines in North China's main food production plain

Agriculture consumes a huge amount of energy every year and then emits lots of greenhouse gases (GHG). Reduction of agricultural energy consumption is important to sustainable agriculture and mitigation of climate change. Groundwater is the main irrigation source in north China's main food production plains, North China Plain (NCP). Many studies have shown that the groundwater levels here have declined a lot during past decades. However, the related environmental and economic impacts have been rarely researched. This study carries out a detailed research on the changes in energy cost and GHG emissions caused by groundwater level declines on the NCP. Results indicate that during 1996-2013, total agricultural groundwater consumption here has increased by 20%. Over-exploitation of groundwater has caused severe groundwater declines (0.6 m yr(-1)) and the decline rate has become faster in recent years. As a result, energy use rate for pumping unit water has increased from 0.50 to 0.61 kWh m(-3), by nearly 22%. Therefore, GHG emissions have increased from 6.16 to 8.72 Mt CO(2)e, by 42%. Hebei suffers the most serious groundwater level declines and emits most GHG from pumping, accounting for 47% of the total emissions in the NCP. The economic cost of energy consumption and emission reduction for pumping irrigation is US$ 1.25 billion in 2013, reaching up to 10.3% of GDP in this region. The increasing cost is a great threat to sustainable development of agriculture. Water-saving irrigation is one of the most effective ways to reduce water and energy consumption without loss of grain output. To reduce GHG emissions and pressures on energy and groundwater resources, water-saving irrigation should be greatly promoted in this region. The study would contribute to the development of water-saving and energy-saving agriculture.