Research On The Spatio-temporal Characteristics Of Drought-Flood Disasters As Well As Cold-Warm Changes Of Southwest China In Qing Dynasty

In recent years,the extreme meteorological disasters events had intensified in China.I collected the historical data of drought and flood disasters and cold-warm events from 1644 to 1991 in Southwest China,established the database of historical drought-flood disasters and cold-warm events data,reconstructed the drought-flood and temperature grade series and verified the reliability by comparing them with the precipitation sequence of western China,the oxygen isotope sequence of Dongge cave and the mean winter temperature of Kunming in this paper.Many modern climate statistical methods,such as the ensemble empirical mode function(EEMD),moving average method,cross-wavelet power spectrum and cross-wavelet coherence spectrum was used to analyze the spatial-temporal evolution of flood and drought disasters as well as cold-warm in Southwest China in Qing Dynasty,and to explore its mechanism.The results show:(1)Collecting and compiling the data of drought and flood disasters in Southwest China from 1644 to 1911,and establishing the historical drought and flood disaster grade of each state and the whole region.By using the trend fitting method,I found that from the whole time series,the drought and flood disaster grade series in Southwest China showed a trend that lasting increase and decline in turn and smoother from 1654 to 1754.(2)The results of temporal characteristics of the drought-flood grade sequence in Southwest China in Qing Dynasty as follow:? The Qing Dynasty was divided into five periods and fitted the trend of drought and flood frequency,I found that the flood disasters in all periods are higher than the drought disasters,and both showed a increasing trend;?There were obvious phased changes in the drought and flood disaster grade series in Southwest China in Qing Dynasty.It has five drought periods and four waterlogging periods by moving average method and accumulative anomaly method;?By using significance test method,the mutation of the drought and flood disaster grade series occurred four times when n=50 and after 1656 the drought turned to be flood;?There are significant cycles of 2.3a,10.7a,26.9a,42.8a and 126.7a in the drought and flood disaster grade series by EEMD.(3)The results of spatial characteristics of the drought-flood grade sequence in Southwest China in Qing Dynasty as follow:?Drought disasters of Southwest China from 1644 to 1911 in Shunqing,Xuzhou,Chongqing,Zunyi and Yunnan state are more serious.Flood disasters in Chengdu,Chongqing and Yunnan state are more occurred frequently;?From the spatial distribution maps of droughts and floods disasters,it can be seen that the region which happened drought disasters also had flood disasters and disasters occurred most frequently in the eastern and central of Yunnan in Southwest China in Qing dynasty;? The average annual disaster distribution map of drought and flood disasters,it was similar to spatial distribution characteristics of the flood and drought disasters,and also some differences.(4)By using cross-wavelet coherence and wavelet phase-spectrum,I found that there are different degrees of correlation between ENSO indexes,sunspot numbers and drought and flood disasters in Southwest China in different time-scales.The cross wavelet power spectrum showed that there is a close relationship from 7 to 16 years,while the wavelet coherence spectrum shows that there is a strong resonance period of from 0 to 6 years.(5)The cold-warm series in Southwest China from 1644 to 1911 was reconstructed and and found the cold index showed a trend that lasting increase and decline in turn and the amplitude is small before 1840,but it had a significant decline and then rise trend from 1840 to 1911 by the trend fitting method.I also analyzed its phased distribution characteristics,mutation characteristics,periodic characteristics,and the relationship between it and ENSO indexes as well as drought-flood grade sequence,the result showed as below:?In Qing Dynasty,the climate of winter in the Southwest China was divided into two cold periods,namely 1778-1809a and 1856-1901a,and one warm period,namely 1660-1690a;?The mutation of the cold-warm sequence of in Southwest China obviously occurred in 1780 by significance test method;?There is a significant 5a quasi-period of the cold-warm series in Southwest China in Qing Dynasty by Fourier analysis;?By using wavelet phase-spectrum,the cold and warm grade series and the ENSO indexes in Southwest China showed that there is a close relationship between the 0-6a cycles;? The drought-flood sequence in the southwestern Qing dynasty was negatively correlated with the winter warm-cold sequence,but the correlation was not significant.