Pathways to balancing water and food for agricultural sustainable development in the Beijing-Tianjin-Hebei Region, China

Groundwater has significantly supported the increase in agricultural output in the Beijing-Tianjin-Hebei (BTH) region. However, the region has faced severe groundwater depletion for decades. To address this, water conservation in agriculture is considered a key strategy to groundwater decline. However, it is facing with a dilemma to suppress groundwater usage or to pursue agricultural production for food security when considering the criteria for sustainable groundwater use. In this study, we propose a comprehensive water-saving scheme and a planting structure optimisation approach to evaluate the thresholds for the water-food trade-off under various agricultural water conservation scenarios. We investigated, the gains and losses of three main agricultural measures to balancing the groundwater budget: (i) Reducing the planting scale (Sca), (ii) Optimising the planting structure (Str), and (iii) Promoting water-saving technologies (Tec), as well as combined pathways of these water-saving measures. The results showed that: (1) Achieving water conservation goals is challenging when applying a single measure. For example, the effect of water conservation would be 558 million m3 yr−1 by merely optimising the planting structure without reducing the planting scale, whereas the effect would be 527 million m3 yr−1 by solely reducing the planting scale according to farmland conservation plan/goals. (2) Under current water resource conditions in the BTH region, increasing crop water productivity (WP) by 11.5 % could balance the groundwater budget in agriculture, while a 19.2 % increase could achieve balance across all sectors. (3) By employing combined water-saving strategies, including optimising in planting scale/structure and improvements in water-saving technologies, groundwater conservation goals could be met with a 9 % increase in WP, provided that the planting scale and structure are adjusted to meet minimum grain production goals. (4) Two critical thresholds distinguish water-saving pathways, highlighting the marginal effects of investing in technological improvement versus optimising planting scale/structure. These results provide a basis for quantifying critical thresholds in cropping system optimising and provide useful information for similar regions worldwide.