Dryness and wetness variations for the past 1000 years in Guanzhong Plain

Abstract

In this study, spatial-temporal statistical technologies were utilized to interpolate a dryness and wetness grade dataset, which was reconstructed from previous Chinese historical documents, but with significant data gaps in the past 1000 years, and a complete grade dataset of dryness and wetness was developed for Guanzhong Plain including seven sites at Linfen, Changzhi, Xi’an, Fengxiang, Luoyang, Nanyang and Hanzhong. The probit model was used to interpolate the missing values at the spatial scale depending on the highest variance explanation between neighbouring stations, and the Markov chain model was used to interpolate the temporal series depending on the known features of the dataset from 1470 to 2010. On the basis of this dataset, long-term variation features and extreme drought and flood events in the Guanzhong Plain were identified. By means of wavelet analysis and ensemble empirical mode decomposition methods, the main cycles of interannual-interdecadal-centennial scales of dryness and wetness variations were detected and the relationships between periodicity and driving forces were analyzed. Results indicated that the dry-wet change of the Guanzhong Plain has had three stages in the past 1000 years, that is, the climate changed from wet to dry in 960–1150, then from dry to wet in 1151–1800, and again from wet to dry after 1801. On the half-centennial time scale, five wet periods in 960–1000, 1151–1200, 1251–1300, 1351–1400 and 1651–1900, and five dry periods in 1001–1150, 1201–1250, 1301–1350, 1401–1650 and after 1901 were identified. Extreme drought and flood events occurred with high frequency in the 17th and 19th–20th centuries, about once every two years. Extreme drought events lasting 5 years occurred in 1070–1089, 1212–1216, 1327–1331, 1431–1445, 1481–1491, 1634–1641, 1688–1692, 1714–1722, 1875–1878, 1925–1931 and 1993–1997. Extreme flood events lasting 5 years occurred in 981–985, 1647–1653, 1658–1664, 1676–1680, 1725–1730, 1848–1854 and 1882–1889. The dry-wet changes of the Guanzhong Plain has an inter-annual oscillation with a 3–7-year scale, inter-decadal oscillations with quasi-10-year, quasi-30-year and quasi-70-year scales and a centennial oscillation with a quasi-100-year scale. The climate of Guanzhong Plain tends to be drier than in a normal year in the year of the occurrence of the El Nino or the following year. On the quasi-70-year scale, the correlation of the Pacific Decadal Oscillations and the dry-wet change shows a positive (negative) relationship before (after) 1435, which suggested that the relationship between them is not stable in the long term. In addition, the solar maximum corresponds to the dry climate. It is worth noting that due to the lack of long climate series, both reconstruction and model simulation approaches are used to study climate change during historical times. The reconstructed dryness and wetness variations for the past 1000 years in Guanzhong Plain may still lack certainty, and in the future, further analyses and comparisons between the reconstructions and simulations need to be conducted, in order to diagnose the dynamic mechanisms of the climate features in Guanzhong Plain.