Determining the optimal groundwater depth for vegetation ecosystems in arid regions based on fuzzy comprehensive evaluation

Study region The Hetao Irrigation District is an arid irrigation district in northern China where groundwater depth regulates natural vegetation in saline wastelands. Maintaining groundwater at an ecologically appropriate depth is important for balancing vegetation conservation and regional water management. Study focus This study developed a multi-level fuzzy evaluation system integrating vegetation structure and biodiversity indicators. A cloud model was used to quantify ecosystem quality across groundwater-depth gradients while accounting for fuzziness and randomness. Polynomial regression was used to characterize the relationship between groundwater depth and ecosystem quality. New hydrological insights for the region Ecosystem quality responded nonlinearly to groundwater depth. Depths of approximately 2–3 m produced the highest ecosystem-quality membership values and relatively low uncertainty, with peak performance near 2.5 m. Both shallower and deeper groundwater conditions were associated with reduced vegetation diversity and ecosystem quality. The 2–3 m range therefore provides a region-specific reference for coordinating ecological protection and groundwater regulation in the Hetao Irrigation District.