With 17 goals, 169 targets and 232 indicators, the Sustainable Development Goals (SDGs) proposed by the United Nations in late 2015 have provided the global community with an elaborate and concrete guidance for international collaboration in improving human well-being while safeguarding long-term global sustainability. However, the complexity and interactions between social, economic and environmental goals remain largely unexplored. This paper aims at making a contribution to filling in this knowledge gap by examining the relationship between environmental sustainability and socio-economic SDGs in the Belt and Road (B&R) region, where many countries are experiencing rapid urbanization and facing severe resource constrains and environmental challenges, such as water scarcity, land degradation, climate change and eutrophication. To that end, this paper accounts for the water, land, carbon, nitrogen and phosphorus footprints of 65 B&R countries in 2015 by employing a global multi-regional input-output (MRIO) model, compares them with downscaled environmental boundaries, and assesses the corresponding environmental sustainability deficit index (ESDI) of all the B&R countries. Moreover, a set of socio-economic indicators chosen from the SDGs dashboard are employed to measure the progress of social development and economic growth in each B&R country using principal component analysis. Furthermore, spatial econometric models are adopted to capture the trade-offs and synergies between environmental sustainability and socioeconomic SDGs. Further discussion is raised on the geospatial division management plan for sustainable development in the B&R region. We find that: (1) The total and per capita environmental footprints in the B&R region show strong spatial heterogeneity, and the land, carbon, nitrogen and phosphorus footprints of most countries have exceeded their corresponding environmental boundaries, showing significant spatial autocorrelation (P<0.01). (2) Socio-economic SDGs related to basic human needs, such as SDG 1 (no poverty) and SDG 3 (good health and well-being), have been fulfilled to large extent while the SDGs like SDG 8 (decent work and economic growth) and SDG 12 (responsible consumption and production) are in urgent need of improvement. (3) The relationships between environmental sustainability and socio-economic SDGs is complicated; that is, goals that have synergies with ESDI can be priorities for SDGs, including SDG 1 (no poverty), SDG 2 (zero hunger), SDG 6 (clean water and sanitation), SDG 9 (industry, innovation and infrastructure), SDG 10 (reduced inequalities) and SDG 11 (sustainable cities and communities). By contrast, goals including SDG 8 (decent work and economic growth), SDG 12 (responsible consumption and production), SDG 16 (peace, justice and powerful institutions) and SDG 17 (partnerships for the goals) show trade-offs with ESDI and therefore should be implemented with caution to avoid potential ecological and environmental risks. For indicators within SDG 5 (gender equality) that counteract the reduction in ESDI, policy actions should be taken to increase synergies and decrease trade-offs. (4) Four types of sustainable development zones are identified on the basis of national environmental sustainability and the SDGs progress: green pilot zone, key development zone, green transformation zone, and risk prevention zone. There is a great need for common but differentiated policies in support of B&R's division management. The research findings are expected not only to bring transparency to the complicated relationship between various SDGs and environmental sustainability, but also to assist policy makers with formulating integrated policies for achieving the SDGs and building the green B&R.
