Tree-Ring Latewood Width Based July–August SPEI Reconstruction in South China since 1888 and Its Possible Connection with ENSO

Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me-teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorological records back for centuries to help us better understand hydroclimatic conditions. In this study, we reconstructed the July–August standardized precipitation–evapotranspiration index (SPEI_Jul–Aug) based on a newly developed 127-yr adjusted latewood width chronology from Tsuga longibracteata, South China. The chronology explained 40% of the actual SPEI_Jul–Aug variance in the period 1953–2014. The reconstructed SPEI_Jul–Aug can represent large-scale July–August SPEI variations over South China, including northern Guangxi, Hunan, and Guizhou provinces. From the perspec-tive of the past 127 years, the extreme summer drought in 2013 was not unusual because more extreme drought events occurred in the first half of the 20th century. A significant 2.0–3.6-yr hydroclimatic cycle existed in the reconstruction, which indicated that the SPEI_Jul–Aug might be driven by El Niño–Southern Oscillation (ENSO). We further checked the time-dependency of the relationship between SPEI_Jul–Aug and ENSO and found that it was unstable. Their relationship was weak before the 1950s, became significant from the 1950s to early 1990s, and then dropped to be weak again and even out of phase since the early 1990s, which may be attributable to the significant westward extension of the western Pacific subtropical high.