Ecological restoration regulates carbon water processes in arid and semi-arid ecosystems, yet its lagged and threshold effects remain unclear. Using multi-source remote sensing data from 2000 to 2022, we identified forest restoration regions, shrubland–grassland restoration regions, and gradual vegetation restoration regions (VRRs) in the Ningxia–Inner Mongolia Reach of the Yellow River and quantified their lagged effects on carbon use efficiency (CUE), water use efficiency (WUE), and carbon-water compound use efficiency (COM) using distributed lag nonlinear models. VRRs dominated restoration, with restoration occurring earlier in the semi-arid area. CUE showed a dominant response at lag 5, whereas WUE and COM showed lagged responses at lag 3–5 in the arid area but immediate responses in the semi-arid area. Restoration thresholds varied by climate. In the arid area, SGRRs and VRRs had a safe restoration range of 23%–48% for annual newly added restoration proportion at the 1-km grid-cell scale, while negative WUE and COM responses emerged when restoration exceeded approximately 60%, associated with lag 3–5 effects. In the semi-arid area, restoration could exceed 60% without adverse effects. FRRs showed a low threshold of 10%–15%, SGRRs an optimal threshold of approximately 52%, and VRRs a higher threshold of 49%–61%. These findings provide a basis for climate-specific ecological restoration that maximizes long-term carbon–water synergies.

Paper Linkage:https://doi.org/10.1016/j.jenvman.2026.131189