Zheng Duan

Highlights: What are the main findings? A ~32-year aridity cycle is detected across China through Fourier spectrum analysis of 1950–2022 aridity data. An arid–humid climate divide is revealed by entropy-based climate stability indicators. Recent remote sensing data show a nationwide expansion of surface water bodies and localized groundwater recovery. What are the implications of the main findings? The identified ~32-year aridity cycle provides a basis for anticipating future dry–wet transitions and improving long-term climate adaptation planning in China. The contrasting response times of surface water and groundwater indicate that surface water responds rapidly to climatic wetting, whereas groundwater shows delayed and regionally heterogeneous responses. Global warming profoundly affects hydrological processes and regional aridity. However, the shifts in the arid–humid transition zone and its relationship to divergent surface and subsurface hydrological responses remain not fully understood. This study investigates the spatiotemporal aridity changes in China using hydroclimate datasets (1950–2022) and examines associated hydrological responses via remote sensing (RS) since the early 2000s. The results reveal that: (1) a pronounced ~32-year oscillatory pattern governs both the expansion and contraction of drylands and non-drylands, with China currently in a wetting phase; (2) a distinct climatic transitional zone is identified, and a distinct boundary emerges separating drylands and non-drylands, here referred to as China’s Arid–Humid Divide, reflecting the climatic equilibrium shaped by multiple monsoon systems and local topography; and (3) the nationwide expansion of surface water bodies, following the increase of groundwater storage in partial areas, was detected via recent RS data. These findings provide new insights into the mechanisms driving long-term aridity transitions and support climate adaptation and sustainable land management in China.