Tree-ring reconstruction of streamflow for Palgong Mountain forested watershed in southeastern South Korea

Tree-ring chronologies from pine,oak and black locust tree species were used to reconstruct annual streamflow and examine hydrological drought years for Palgong Mountain forested watershed in southeastern South Korea for the period from 1954-2015. The backward elimination multiple regression analysis provided the statistically significant predictor chronologies of streamflow. The final calibration and verification test models accounted for 84.8% and 81.6%,respectively,of the variability in streamflow observed in the gage data. Further verification of the validity of the reconstructed model was undertaken with the Pearson Correlation Coefficient,the Reduction of Error Test,and the Durbin-Watson Statistics and indicated fidelity of the model for reconstructing the annual streamflow. Analyses of the reconstructed annual streamflow indicate that the most persistent years of high flows above the median annual discharge occurred from 1986-2008.This period included 7 single or multiple years of highest flow above the 90 th percentile discharge and multiple years of high flows with a time interval of 2-6 years,although with intervening multiple years of low flows below the 10 th and 50 th percentile. In comparison,the most persistent years of low flows below the median annual discharge occurred from 1954-1985 and 2009-2015. This period included 8 single or multiple years of lowest flow below the 10 th percentiledischarge and multiple years of low flows with a time interval of 2-9 years,although also with intervening multiple years of high flows above the 50 th percentile. No single years of extreme hydrological droughts below the 10 th percentile were identified from 1986-2015 whereas a greater proportion of high flows above the 90 th percentile occurred during this period. The persistent single or multiple years of lowest flows between 1954 and 1985 were the recent most critical hydrological drought years identified in the Palgong Mountain forested watershed providing supportive evidence of the severity of past hydrological droughts during that period,applicable to the southeastern South Korea where the study watershed is located. This interpretation agrees with the hydrological drought event years identified from 1951 to the early 1980 s in a related national study that used precipitation proxy data to reconstruct past occurrences of droughts in Korea.