Evaluating water resource sustainability from the perspective of water resource carrying capacity, a case study of the Yongding River watershed in Beijing-Tianjin-Hebei region, China

China is facing great challenges to balance its natural water resource use and eco-environment protection, especially in the north semi-arid region with large water consumption due to the rapid economic growth. This highlights the urgency to use water resource carrying capacity (WRCC) as a measure to maintain the sustainable development of the human and natural water system. Here, we used a coupled model based on the system dynamics and cellular automaton models to assess the WRCC under the critical value of water resource withdrawal ratio (40%) and its sustainability in the Yongding River watershed in Beijing-Tianjin-Hebei region, where the water use highly depends on river flow and nonrenewable groundwater resources. The analytical results showed that the current regional WRCC is severely overloaded due to strong human activities. The predicted results based on four scenarios, i.e., existing development, water saving, industrial restructuring, and integrated development schemes, showed that although the improvement of water saving and water use efficiency has mitigated the regional water shortage, evidenced by the increased WRCC, the water shortage would continue due to the increased water demand. Under the integrated development scenario, it will need at least additional 7.1 x 10(8) m(3) water per year (Beijing: 2.5 x 10(8) m(3), Tianjin: 0.8 x 10(8) m(3), Hebei: 3.8 x 10(8) m(3)) via the water transfer project to maintain the sustainability in the next decades. Our research provides recommendations for reasonable water utilization and supplementation under the severe water crisis.