May–June relative humidity variation recorded by tree ring widths of Pinus armandii Franch since 1863 in the Funiu Mountains, central China

Long-lasting drought records can provide valuable insights into the history of hydroclimate change in central China, but meteorological records are too short to capture long-term variability of the humidity. In this study, we established a tree-ring width chronology of Pinus armandii Franch in the Funiu Mountains region of central China. Correlation analyses showed that tree radial growths were mainly limited by hydrothermal combination in May–June. The results of the moving correlation analysis further showed that the response relationship between tree growth and relative humidity in May–June (RH_MJ) was the most stable. This relationship has been reconstructed since 1863. The variance of the reconstructed RH_MJ was explained by 41.7% (40.6% after adjusting for degrees of freedom). Over the past 158 years, there were 3 wet periods and 4 dry periods. The spectral analysis revealed that the reconstructed RH_MJ exhibited quasi-periods of 2-4a and 31.6a, and cross-spectrum analysis showed that the reconstructed RH_MJ may be related to ENSO, PDO, solar activity and the East Asian summer monsoon. The spatial correlation analysis revealed that the reconstructed RH_MJ accurately depicted the fluctuations in humidity within the Huanghe-Huaihe Plain. Furthermore, the reconstructed RH_MJ exhibited a strong negative correlation with the sea surface temperature (SST) of the subtropical North Pacific, while it displayed a highly significant positive correlation with the SST of the eastern equatorial Pacific from the previous May to the current April. This also indicated a possible link between humidity fluctuations in the Huanghe-Huaihe Plain and the Pacific internal variability in climate system. Therefore, this research aims to expand and complement the existing meteorological records, providing important reference significance for forest management, agriculture, and animal husbandry.