Spatio-Temporal Characteristics And Influencing Factors Of Extreme Dry/Wet Events In In China's Oases During 1960-2019

Under the background of global warming,extreme climate events have occurred frequently around the world,which has had a huge impact on human society,economic development and ecological environment construction,and has also caused a series of crises to world food,water resources and energy security.China's oases live deep in the hinterland of Eurasia and are distributed in arid and semi-arid areas of China.The large-scale extreme dry/wet events will lead to the change of agricultural production distribution in China's oases and seriously restrict the socio-economic development in oases.At present the study of China's oases extreme dry/wet events mainly concentrated in the fixed threshold based on different drought index for extreme dry/wet events happened frequency,intensity and variation characteristics of research,and focus on a single small area in China's oases,and the standardization of surface wetness index variables based on month of China's oases all regional extreme dry/wet research mechanism and influencing factors of the events almost rarely meet.Therefore,it is of great significance for the development of regional agricultural production and ecological construction to explore the spatio-temporal characteristics of extreme dry/ wet events and their influencing factors in China's oases.Based on the diurnal mean temperature,maximum temperature,minimum temperature,relative humidity,wind speed,sunshine duration and precipitation data of 63 national meteorological stations in China's oases from 1960 to 2019,the long-term series of extreme dry/wet events in China's oases were calculated.Based on Sen's slope,Kendall-Tau nonparametric test,empirical orthogonal function decomposition,Fourier power spectrum and regime shift detection test,the temporal and spatial variation characteristics,period and pattern changes of extreme wet/dry events were analyzed at different time scales.At the same time,the contribution rate was used to quantitatively analyze the contribution degree of major meteorological factors to the change of extreme dry/wet events.Combined with the atmospheric circulation index and NCEP/NCAR reanalysis data,partial least squares,cross wavelet and bilinear interpolation were used.To explore the possible relationship between the frequency variation of extreme dry/wet events in China's oases and the atmospheric circulation factors,geopotential height field,SST field and ENSO event,and to reveal the influence of regional atmospheric circulation and SST background field on the extreme dry/wet events in oases in China's oases.The research conclusions are as follows:(1)From 1960 to 2019,the frequency of extreme drought and extreme wet events in China's oases decreased and increased significantly at the rate of-0.24/10 a and 0.19 /10 a,respectively.Except for the oasis in Hetao Plain,the frequency of extreme drought events in the other five sub-oases showed a decreasing trend,while the frequency of extreme wet events showed an increasing trend.Extreme drought events occurred frequently in 1960 s,while extreme wet events occurred frequently in 2010 s.The frequency of extreme drought events in all seasons showed a decreasing trend,while the frequency of extreme wet events showed an increasing trend.Both extreme drought and wet events occurred the most frequently in July.(2)The main spatiotemporal modes of the occurrence frequency of extreme drought events in China's oases are consistent in the whole region except for some parts of the oasis in Hetao Plain,and the main spatiotemporal modes of the occurrence frequency of extreme wet events are consistent in the region.Extreme drought events of Spring active area distribution in Yinchuan plain oasis area,frequency,high value center in the Zhongwei city of the summer,the autumn highfrequency sub-region in karamay,winter active area in the Jiuquan city,the humid season extreme wet events active region distribution respectively in Tuli county of Tacheng prefecture,Dulan county of Haixi prefecture,Fuhai county of altay prefecture,Fukang city of Changji prefecture.(3)Regime Shift Detection analysis showed that the frequency of extreme drought events in China's oasis mutated in 1986 and 2015,while that of extreme wet events mutated in 1989 and 2015.Fourier power spectrum analysis shows that the frequency of extreme drought events in China's oasis has a cycle of 5.69 years,and the frequency of extreme wet events has a cycle of 2.12 years and 2.35 years.(4)The analysis of influencing factors showed that the contribution rates of major meteorological factors to the surface dry/wet of China's oasis were as follows: precipitation >maximum temperature >average temperature >wind speed >relative humidity >sunshine hours;The extreme drought events are mainly affected by the Qinghai-Tibet Plateau index,and the extreme wet events are mainly affected by the area and intensity of the polar vortex in the northern hemisphere.The 500 h Pa geopotential height field in the northern hemisphere is mainly negatively correlated with extreme drought events,and positively correlated with extreme wet events.Extreme dry/wet events in China's oasis are significantly correlated with ENSO index at multiple time scales.The sea area around the equatorial Pacific Ocean(3°?9°N,140°E?179°W)is the key sea area affecting the change of extreme dry/wet events in China's oasis.