Spatial And Temporal Variation Of Precipitation In China

Precipitation is one of the most important climatic indices and the most basic step in water cycle.Its variation is very complex due to the impacts of many factors such as the general atmospheric circulation,latitude,elevation and terrain.The uneven spatial and varying temporal distribution of precipitation can directly cause meteorological disasters such as droughts and floods.Therefore,observations of precipitation and the analysis of its spatiotemporal variation can serve as references for predicting and preventing floods and droughts.It is very crucial for industrial and agricultural production,food security,water development,flood control of rivers,engineering management,reducing socio-economic loss and ensuring people's security of property and lives.Since in summer and fall(from June to November),precipitation is at higher level than that in winter and spring,precipitation in summer and fall has decisive influence on annual total precipitation.Therefore,this research focuses on spatial and temporal variation of summer and fall precipitation,based on daily precipitation data at 756 national ordinary,reference and automatic meteorological stations from 1954 to 2017,these stations cover 31 provinces,autonomous regions and municipalities across China.This research employed appropriate methods according to different types of sample data,to make estimation results accurate and credible.First of all,linear trend analysis,Mann-Kendall test and moving t-test were employed on summer and fall total precipitation as well as precipitation intensity,in order to determine the directions,significance and abrupt change points of the trends.Theil-Sen slope estimation was adopted towards series with extreme precipitation,to robustly estimate change rate of trends and eliminate the impact of outliers.Then based on the feature of overdispersion and following discrete and skewed distribution,a trend analysis on maximum consecutive dry days(CDD)was carried out by(quasi)Poisson regression model,and variation of extreme dry condition in summer and fall was revealed.Then average consecutive dry days(ACDD)index was proposed based on the definition of CDD,which can measure overall dry condition.According to its feature of following continuous,skewed distribution,stochastic ordering theory and non-parametric El Barmi-McKeague test were introduced to compare ACDD in 3 periods: 1960-1965,1985-1990 and 2010-2015 in the sense of probability distribution,and changes in precipitation patterns were analysed combining the variation of multiple precipitation indices.Then inverse distance weighting,radial basis functions and Kriging interpolation methods were implemented on average annual summer and fall total precipitation as well as precipitation intensity,to analyse spatial distribution of precipitation in the two seasons.Finally,hierarchical clustering and k-means were employed on yearly summer and fall total precipitation in all regions to obtain precipitation regionalization based on optimal clustering results,and precipitation characteristics of different sub-regions were interpreted.Precipitation regionalization results in the 1960 s,1970s,1980 s,1990s and 2000 s were compared,link between dynamic changes of precipitation regionalization results and inter-decade fluctuations of precipitation was established.Based on the researches above,main conclusions are as follows:1.There are 5 regions(Jiangxi,Qinghai,Shanghai,Xinjiang and Zhejiang)showing significant increasing trends in summer total precipitation from 1954 to 2017,abrupt changes mainly happened before the year 2000,which were all increasing abrupt changes.3 regions(Beijing,Hebei and Tianjin)show significant decreasing trends without abrupt changes.18 regions show significant increasing trends in summer precipitation intensity,including Chongqing,Fujian,Guangdong,Guangxi,Guizhou,Heilongjiang,Hunan,Jiangsu,Jiangxi,Jilin,Liaoning,Qinghai,Shaanxi,Shandong,Shanghai,Xinjiang,Yunnan and Zhejiang,with abrupt changes mainly happening before 2000.8 regions(Anhui,Beijing,Hebei,Liaoning,Ningxia,Shaanxi,Shanxi and Tianjin)which are mainly located in northern China show significant increasing trends in summer maximum consecutive dry days,while 5 southern regions(Fujian,Guizhou,Sichuan,Yunnan and Zhejiang)show significant decreasing trends,indicating that extreme drought condition changes in opposite directions in north and south China.2.Only Xinjiang has a significant increasing trend in fall total precipitation,with increasing abrupt change in the year 1980,while 2 regions(Jilin and Liaoning)show significant decreasing trends,with no abrupt changes.There are 23 regions showing significant increasing trends in fall precipitation intensity,including Anhui,Beijing,Chongqing,Fujian,Guangdong,Guangxi,Guizhou,Hainan,Hebei,Henan,Hubei,Hunan,Jiangsu,Jiangxi,Qinghai,Shaanxi,Shanghai,Sichuan,Tianjin,Xinjiang,Xizang,Yunnan and Zhejiang,with abrupt changes mainly happening before 2000.7 regions(Heilongjiang,Jiangsu,Jilin,Liaoning,Shanghai,Tianjin and Xizang)show significant increasing trends in fall maximum consecutive dry days,while 3 regions(Gansu,Neimenggu and Sichuan)show significant decreasing trends.3.Comparing summer ACDD in 3 periods(1960-1965,1985-1990 and 2010-2015),results show that summer ACDDs in all regions except Hunan,Xinjiang and Zhejiang increase stochastically from period 1 to period 2 or 3,or from period 2 to period 3,indicating that average duration of drought in summer has prolonged in China.In addition,summer precipitation patters in 9 regions(Anhui,Fujian,Guangdong,Guangxi,Hubei,Jiangsu,Jiangxi,Qinghai and Shanghai)have changed.Precipitation days and dry days tend to appear intensively,increasing occurrence rate of droughts and floods.Such precipitation change rule was revealed by ACDD,but was not reflected by precipitation indices such as total precipitation,precipitation intensity,precipitation days and CDD.4.Kriging gives the most accurate result in interpolation analysis of average summer total precipitation over 1954-2017.Interpolation map indicates that south Yunnan,south Guangxi,south Guangdong,and Hainan have large amount of average summer precipitation,while Xinjiang,northwest Xizang,northwest Qinghai,Gansu and west Neimenggu have low level of precipitation.Kriging gives the most accurate result in spatial interpolation of summer precipitation intensity as well,interpolation map indicates that south Yunnan,Guangxi,Guangdong,Hainan,central Sichuan,south Anhui and southeast Zhejiang have high precipitation intensity,while Xinjiang,northwest Gansu,west Neimenggu,northwest Xizang and northwest Qinghai have low precipitation intensity.Some areas in southeast Liaoning and southeast Jilin have slightly larger precipitation intensity than other areas within the provinces.In terms of fall total precipitation,Kriging gives the most accurate interpolation result.Compared to summer,in fall,regions with abundant precipitation in southwest Yunnan,Chongqing and southeast Zhejiang expand,and wet regions in central Sichuan,north Anhui,south Guangxi and south Guangdong shrink.On the other hand,dry regions in southeast Neimenggu,north Hebei,north Shanxi,north Qinghai,and northwest Xizang expand.Kriging gives the most accurate result in spatial interpolation of fall precipitation intensity as well.Compared with summer,regions with relatively high precipitation intensity in southwest Yunnan,Chongqing,central Hunan and southeast coast in Zhejiang expand,while regions with relatively high precipitation intensity in south Anhui,central Sichuan,Guangxi,Fujian and Guangdong shrink.On the other hand,regions with relatively low precipitation intensity in central and east Neimenggu,Hebei,west Northeast China,north Shanxi,central and west Xizang expand.5.For time span of 1954-2017,summer precipitation regionalization result based on clustering analysis contains 4 clusters,roughly representing Northwest China,Northeast and North China,East,Central and Southwest China,and South China respectively,with precipitation increasing from Cluster 1 to Cluster 4.Fall precipitation regionalization result contains 5 clusters,roughly representing Northwest China,Northeast and North China,Central China,Southwest,South and East China,and Hainan respectively,with precipitation increasing from Cluster 1 to Cluster 5.Both summer and fall precipitation in Northeast and North China decreases significantly.Precipitation regionalization results are very different in the 1960 s,1970s,1980 s,1990s and 2000 s.Most regions transfering from clusters with low precipitation to those with high precipitation have increased precipitation among decades,while most regions transfering from clusters with high precipitation to those with low precipitation have decreased precipitation among decades.