Latewood Tree-Ring Δ13C Reconstruction of August–September SPEI in Northwestern Hubei, Central China, Since 1839

Hydroclimatic variability in Central China affects forest ecosystem stability, agricultural production, and regional water resources, but short instrumental records limit the long-term evaluation of recent droughts. We developed earlywood and latewood tree-ring carbon isotope discrimination (Δ13C) chronologies of Pinus massoniana from Zhushan County, Hubei Province, and reconstructed August–September Standardized Precipitation Evapotranspiration Index (SPEI) variability. During 1951–2018, latewood Δ13C showed the strongest relationship with August–September SPEI (r = 0.646, p < 0.001), and the linear regression model explained 41.7% of the observed variance. Sequential leave-20-out calibration–verification tests supported the model’s stability and predictive skill. The 1839–2022 reconstruction provides a 184-year record characterized by pronounced interannual variability and lower-frequency changes. Fourteen extreme dry years and six extreme wet years were identified using the mean ± 1.5 standard deviation criterion. The most severe dry years were 1900, 1928, 1923, 1999, and 2016, indicating that several recent droughts were also prominent in the long-term context. Spatial correlations showed that the reconstruction primarily represents moisture variability over Hubei Province and adjacent parts of Central China. These results support latewood Δ13C as a seasonal proxy for late-growing-season water-balance variability in humid subtropical forests.