The salinity-aridity nexus modulates eco-hydrological impacts of vegetation enhancement and desertification across saline-alkali drylands in northern China

Vegetation dynamics in drylands fundamentally restructure the land-atmosphere interface, yet the resulting surface water-energy coupling across saline-alkali environments remains insufficiently understood due to the complex interplay between climatic aridity and edaphic salinity. By integrating multi-decadal satellite observations with a biogeophysical decomposition framework, we quantified the growing-season impacts of vegetation enhancement (cropland expansion and grassland restoration) alongside desertification across the saline-alkali drylands of northern China from 2003 to 2020. Our results demonstrated that vegetation enhancement induced significant localized surface cooling, peaking in barren-to-cropland conversions (−0.674 ± 0.02 K), followed by grassland-to-cropland conversions (−0.066 ± 0.007 K) and barren-to-grassland restoration (−0.017 ± 0.009 K), whereas desertification exhibited a subtle warming tendency (+0.005 ± 0.0003 K). These thermal responses were primarily governed by non-radiative, evapotranspiration-mediated processes. Furthermore, the salinity-aridity nexus modulated regional energy partitioning through two divergent hydro-edaphic pathways. In reclaimed irrigated cropland, management interventions alleviated ambient matric and osmotic constraints, while intensifying regional water consumption. In contrast, non-irrigated restored grasslands exhibited a functional decoupling between canopy greening and evaporative cooling, reflecting conservative stomatal regulation enforced by compound soil matric and osmotic stresses. The marginal warming accompanying desertification indicated an impaired surface evaporative buffer following vegetation loss and secondary salinization. By elucidating how the salinity-aridity nexus modulates land-surface water-energy coupling, these findings highlight the necessity to align restoration strategies with local hydro-edaphic capacities, balancing the microclimatic cooling of irrigated agriculture against the long-term hydrological sustainability of natural grasslands under accelerating global change.