Attributing trends in the environmental intensity of crop production
Our study highlights the cropland shift in China driven by urbanization challenged the progress towards sustainable intensification of agriculture system.
The paper in Nature Sustainability is here: https://go.nature.com/2sZH21L
Dated from the middle of 1990s, a group at Institute of Remote Sensing Application (now Aerospace Information Research Institute), CAS started to build a national land-use database of China (NLUD-C) based on remote sensing images. I joined the group as a graduate student in 2005. At that time, the NLUD-C already included land-use of China in three time-points (late 1980s, 1995, and 2000). We were about to update the NLUD-C to 2005. However, there was no external funding available. The group leader, Zengxiang Zhang, aware of the importance of building up a database to monitor the long-time change of land-use in China, continued the work. Now, we got seven time-points of land-use in China, which helps us understand the trajectory of land-use change in China and also provide a bunch of valuable data for land-related research.
When looking into land-use change of China based on the NLCD-C, we found urban has been expanding very rapidly, taking up lots of fertile cropland nearby cities. However, to produce enough food, cropland expanded in northern part of China, where harvest index is lower than in southern China, namely productivity is lower in north. Besides, cropland expansion is concentrated in northwest of China after 2000, where ecosystem is vulnerable. We were curious about quantitative impacts of these changes on food production as well as the environment.
Fortunately, I got a chance to work in Global Landscape Initiative (GLI) group of Institute on Environment in University of Minnesota, as a visiting scholar funded by CAS in 2014. GLI group has done leading research about the strategies on how to feed global population while minimizing environmental impacts. James Gerber and Paul West, the co-leaders of the group, were very interested and supportive on the land-use related research in China. I also got support from Kimberly Carlson and Graham MacDonald, who were doing their postdoc research in GLI group at that time, and Kate Brauman, who had just started her Global Water Initiative. Their expertise on research on GHG emission, land-use change, and water greatly helped shape this paper.
At the beginning, I thought land-use change would have large effects on total food production and environmental impacts. However, the results showed that the overall effects of land-use change in China was small, as cropland loss was balanced by cropland expansion at the national level. Most of the changes in crop production and environmental impacts were actually resulted from farm management changes in national level. But when we zoom into regional level, the role of land-use change was quite important, and was becoming larger as time pass by. For example, in the middle and lower reaches of Yangtze River, land-use change offset 18% of production gain from farm management from 1987 to 2010. This contribution increased from 10% (between 1987 and 2000) to 32% (between 2000 and 2010). In the arid northwestern China Gan-Xin region, cropland expansion explained 46% of the increase in irrigation water consumption from 1987 to 2010. This contribution reached 84% in the 2000-2010 period. If this spatial shift of cropland distribution continued, it would not only place great pressures on regional crop production and environment, but also cause large amount of national trade, leading to additional food lost and energy consumption.
Urbanization is a global concern when it comes to food security, and nearly 80% of expected cropland loss to urban areas will likely occur in Asia and Africa, where 76% of the global population lives. This kind of cropland expansion on marginal land driven by urban expansion is very likely to happen in other urbanization area. To feeding global population with minimum environmental impacts, it is critical to take advantage of the potential of sustainable intensification on existing cropland while avoiding negative impacts of urbanization.