Water footprint and virtual water trade of China: past and future.
The long-term sustainability of human water consumption is being challenged by climate change, population growth, socioeconomic development and intensified competition for finite water resources among different sectors. With a focus on crop production, consumption and trade of China, this study quantifies the inter-annual variability and developments in consumptive (green and blue) WFs and VW trade in China over the period 1978-2008 (Part 1) and assesses consumptive WFs and VW trade of China under alternative scenarios for 2030 and 2050 (Part 2). It considers five driving factors of change: climate, harvested crop area, technology, diet, and population. Evapotranspiration, crop yields and WFs of crops are estimated at a 5×5 arc-minute resolution for 22 crops. Four future scenarios (S1-S4) are constructed by making use of three of IPCC's shared socioeconomic pathways (SSP1-SSP3) and two of IPCC's representative concentration pathways (RCP 2.6 and RCP 8.5) and taking 2005 as the baseline year. Results show that, over the period 1978-2008, crop yield improvements helped to reduce the national average WF of crop consumption per capita by 23%, with a decreasing contribution to the total from cereals and increasing contribution from oil crops. The total consumptive WFs of national crop consumption and crop production, however, grew by 6 and 7%, respectively. Historically, the net VW within China was from the water-rich South to the water-scarce North, but intensifying North-to-South crop trade reversed the net VW flow since 2000, which amounted 6% of North's WF of crop production in 2008. China's domestic inter-regional VW flows went dominantly from areas with a relatively large to areas with a relatively small blue WF per unit of crop, which in 2008 resulted in a trade-related blue water loss of 7% of the national total blue WF of crop production. By 2008, 28% of total water consumption in crop fields in China served the production of crops for export to other regions and, on average, 35% of the crop-related WF of a Chinese consumer was outside its own province. Across the four future scenarios and for most crops, the green and blue WFs per tonne will decrease compared to the baseline year, due to the projected crop yield increase, which is driven by the higher precipitation and CO2 concentration under the two RCPs and the foreseen uptake of better technology. The WF per capita related to food consumption decreases in all scenarios. Changing to the less-meat diet can generate a reduction in the WF of food consumption of 44% by 2050. As a result of the projected increase in crop yields and thus overall growth in crop production, China will reverse its role from net VW importer to net VW exporter. However, China will remain a big net VW importer related to soyabean, which accounts for 5% of the WF of Chinese food consumption (in S1) by 2050. The past of China shows that domestic trade, as governed by economics and governmental policies rather than by regional differences in water endowments, determines inter-regional water dependencies and may worsen rather than relieve the water scarcity in a country. All future scenarios show that China could attain a high degree of food self-sufficiency while simultaneously reducing water consumption in agriculture. However, the premise of realizing the presented scenarios is smart water and cropland management, effective and coherent policies on water, agriculture and infrastructure, and, as in scenario S1, a shift to a diet containing less meat.