Water ecosystem service justice within socio-ecological constraints: Spatial assessment and governance implications for the Tarim River Basin

Water scarcity in arid inland river basins is becoming increasingly intertwined with uneven spatial development, ecological vulnerability, and competing demands among production, living, and ecological spaces. However, conventional supply–demand assessments often pay limited attention to the spatial justice of water ecosystem service outcomes. Taking the Tarim River Basin as a case study, this study integrated the water security index (WSI), water distribution equity index (WDEI), and water-use efficiency index (WUEI) to develop an outcome-oriented spatial assessment framework for water ecosystem service justice (WESJ). Moreover, the framework was applied to the period 2000–2020 through pixel-level calculation, county-level aggregation, and basin-level comparison. The results show that WSI was concentrated mainly in agricultural and urban oasis areas, while low estimated pressure in headwater and marginal areas should be interpreted together with ecological vulnerability. The water ecosystem service load index increased over the study period and became spatially concentrated, especially in the Hotan–Kashgar region. Additionally, the WDEI indicated generally limited local differentiation in water-resource load, although regional differences and localized imbalance hotspots persisted. The WUEI did not show consistent basin-wide improvement and remained the largest contributor to diagnosed deficits in WESJ. At the integrated level, the mean county-level WESJ increased modestly, but county-level trajectories diverged, distributional heterogeneity widened, and a statistically significant year-specific spatial clustering signal emerged in 2020. This study extends water ecosystem service assessment from supply–demand balance toward an outcome-oriented justice diagnosis and provides spatial references for differentiated water governance in arid river basins.