Reconstruction of sunspot activity, cold and warm events, and drought and flood events in the central plain of China during the northern Song Dynasty using historical documents

Abstract

The Northern Song Dynasty was an important and prosperous dynasty in the history of China, and it existed during a period of climate abnormality. Climate change research for the Northern Song Dynasty era has significance for understanding the interaction between agricultural civilizations in the central plains and nomadic populations in northern China, transfer of the economic and cultural centers of China, and the vicissitudes of the Northern Song Dynasty. There is currently considerable disagreement regarding climate change in the Central Plain during the Northern Song Dynasty era. Many precious and valuable historical documents and records about the Northern Song Dynasty have been collected, and abundant records of sunspot activity, cold and warm weather, drought and flood events have been compiled. Using the Mann-Kendall test, wavelet analysis, R/S analysis, and frequency analysis etc. mathematical statistics methods, sunspot activity, cold and warm events, and drought and flood events were quantitatively reconstructed. There are 15 sunspot maximum years and 16 sunspot minimum years, the cycle length of sunspot activity is 8–14 years, and the average cycle length is 11 years. Hot years account for 11.3% of the total years; warm years account for 12.7%; cold years account for 20.7%; and freezing cold years account for 3.3%. Mann-Kendall test results show that cold and warm variations are natural fluctuations, and there is no indication of abrupt climate change during the Northern Song Dynasty. Morlet wavelet analysis indicates that there are weak high-frequency oscillations and short oscillation periods with three years before 1052 AD, and there are oscillation periods of six years and clear alternations between warmth and cold during 1060-1120 AD. R/S analysis indicates that the Hurst index (H) of cold and warm index series is 0.6155, and the fractal dimension (D) is 1.3845. Since 0.5 < H < 1 and 1 < D < 1.5, fractal structures are evident in the time series of cold and warm indexes, past increments are positively correlated with future increments, and the average cycle length in the time series for cold and warm indexes is 6 years. Temperatures first decreased rapidly followed by a slow increase with long-term fluctuations, and the mean temperature during the Northern Song Dynasty era is 0.4 °C higher than that in the period 1880–1979 AD. Severe drought, moderate drought, moderate flood, severe flood and normal years account for 15.3%, 25.3%, 11.3%, 6.7%, 41.4% of all years, respectively. Frequency analysis indicates that cooling, warming, drought and flood events show a close relationship to sunspot activity.