Evaluation of the Coupling Coordination and Sustainable Development of Water–Energy–Land–Food System on a 40-Year Scale: A Case Study of Hebei, China

Driven by economic expansion, urbanization, and population growth, the world is witnessing an escalating demand for water, energy, land, and food, posing substantial threats to the sustainable development of societies and economies. Given the intricate interdependencies inherent within the water–energy–land–food (WELF) system, it is imperative to conduct comprehensive assessments of the coupling coordination and sustainable development of the WELF system over long time scales and diverse characteristic dimensions. This study selects Hebei province, China, as the research region, constructing a comprehensive indicator system spanning from 1980 to 2020 using three dimensions: reliability (Rel), robustness (Rob), and equilibrium (Equ). The degree of coupling coordination (DCC) and sustainable development index (SDI) were developed using the comprehensive evaluation index and coupling coordination degree model. Additionally, the obstacle degree model and gray relational degree model were employed to assess the indicators that hinder or promote the SDI. The results indicate that: (1) The DCC (range of 0–1, bigger the better) of the WELF system increased from 0.65 to 0.75 between 1980 and 1998, then fluctuated between 0.75 and 0.69, stabilizing at a moderate level of coordinated development after 2015. (2) For the WELF system in Hebei, as Rel increased, Rob decreased, and Equ increased; similarly, as Rob increased, Equ also increased. (3) The SDI (range of 0–1, bigger the better) rose from 0.45 in 1980, initially increased, then decreased, and eventually stabilized. After 2014, it experienced rapid growth, reaching 0.54 by 2020, indicating an improvement in sustainable development capability. (4) Indicators related to the Equ dimension and the land subsystem were more critical limiting factors for SDI development, while indicators related to the Rel dimension and the food subsystem were more significant contributors to SDI development. These findings offer a scientific foundation and practical insights for Hebei and comparable regions, aiding in the resolution of resource conflicts, optimization of resource allocation, and enhancement of regional sustainable development.