Temporal-spatial Variation Characteristics of the Extreme Precipitation Days over South China from 1961 to 2010

[ Objective] The research aimed to analyze temporal-spatial variation characteristics of the extreme precipitation days over South China from 1961 to 2010. [ Method] Based on the daily precipitation data in meteorological stations over South China, extreme precipitation thresholds were determined according to the percentiles distribution for different stations. Temporal-spatial variation characteristics of the extreme precipitation days over South China were studied by the methods of fuzzy clustering, trend coefficient, wavelet analysis and cross spectrum analysis, etc. [ Re- suit] Four sub-regions were identified over South China. They were respectively Nanling area, west Guangxi area, Coast area and Hainan area. Occurrence seasons of the extreme precipitations in each sub-region were significantly different. Extreme precipitation clays in four sub-regions all had increase trends, and those of Nanling area and Coast area were significant. From wavelet analysis and cress spectrum analysis, there were significant periodic variation characteristics. Extreme precipitation days in each sub-region all had significant same-phase evolution trends at the peri- od of 2 -5 years, but backward time length was different. [ Conclusion] The research provided background materials for forecast and influence as- sessment of the extremely heavy precipitation over South China.

Temporal Variability of Extreme Precipitation in Jiangxi during 1961-2018

Using 58 years (1961 to 2018) of daily rainfall data, this study focuses on determining trends in the annual and seasonal precipitation extremes of Jiangxi, China, by choosing four extreme precipitation indices, including strong precipitation amount (SPA), mean precipitation intensity (MPI), strong precipitation days (SPD), and strong precipitation frequency (SPF). The monotonic trends are tested by using the Mann-Kendall test for the trends and Sen’s method for the magnitude of the trends. The effective sample size (ESS) method was used to eliminate the influence of serial correlation in the Mann-Kendall test. The results indicated that station Zixi had the strongest extreme precipitation, while Wanzai had the weakest. The trends for each index showed an obvious regional feature over Jiangxi. Increasing trends in annual extreme precipitation indices were found at almost all stations, and the annual variability of the extreme precipitation indices was pronounced, especially for the mean precipitation intensity and the strong precipitation frequency;the majority of these positive trends were shown by the statistical tests. In spring, four indices exhibited significant increasing trends in Northeast and Southwest Jiangxi;however, in summer, only MPI had a remarkable positive trend across almost all of Jiangxi. For the other indices, few stations had remarkable trends. In autumn, MPI and SPF showed remarkable increasing trends in most regions of Jiangxi, while SPA and SPD showed increasing trends at only 6 stations and 3 stations, respectively, which were scattered in the northern and middle parts. In winter, the stations with remarkable upward trends in SPA and SPD were mainly located in the middle of the region, whereas the significant patterns of MPI and SPF were located in the south and middle of the region.

Trends in Graded Precipitation in China from 1961 to 2000

Daily precipitation rates observed at 576 stations in China from 1961 to 2000 were classified into six grades of intensity, including trace （no amount）, slight （≤ 1 mm d^-1）, small, large, heavy, and very heavy. The last four grades together constitute the so called effective precipitation （〉 1 mm d^-1）. The spatial distribution and temporal trend of the graded precipitation days are examined. A decreasing trend in trace precipitation days is observed for the whole of China, except at several sites in the south of the middle section of the Yangtze River, while a decreasing trend in slight precipitation days only appears in eastern China. The decreasing trend and interannual variability of trace precipitation days is consistent with the warming trend and corresponding temperature variability in China for the same period, indicating a possible role played by increased surface air temperature in cloud formation processes. For the effective precipitation days, a decreasing trend is observed along the Yellow River valley and for the middle reaches of the Yangtze River and Southwest China, while an increasing trend is found for Xinjiang, the eastern Tibetan Plateau, Northeast China and Southeast China. The decreasing trend of effective precipitation days for the middle- lower Yellow River valley and the increasing trend for the lower Yangtze River valley are most likely linked to anomalous monsoon circulation in East China. The most important contributor to the trend in effective precipitation depends upon the region concerned.

Analysis of China's Haze Days in the Winter Half-Year and the Climatic Background during 1961–2012

The characteristics of haze days and the climatic background are analyzed by using daily observations of haze,precipitation,mean and maximum wind speed of 664 meteorological stations for the period of 1961–2012.The results show that haze days occur significantly more often in eastern China than in western China.The annual number of haze days is 5–30 d in most parts of central-eastern China,with some areas experiencing more than 30 d,while less than 5 d are averagely occurring in western China.Haze days are mainly concentrated in the winter half-year,with most in winter,followed by autumn,spring,and then summer.Nearly 20%of annual haze days are experienced in December.The haze days in central-eastern China in the winter half-year have a significant increasing trend of 1.7 d per decade during 1961–2012.There were great increases in haze days in the 1960s,1970s and the beginning of the 21st century.There was also significant abrupt changes of haze days in the early 1970s and 2000s.From 1961 to 2012,haze days in the winter half-year increased in South China,the middle-lower reaches of the Yangtze River,and North China,but decreased in Northeast China,eastern Northwest China and eastern Southwest China.The number of persistent haze is rising.The Longer the haze,the greater the proportion to the number persistent haze.Certain climatic conditions exacerbated the occurrence of haze.The correlation coefficient between haze days and precipitation days in the winter half-year is mainly negative in central-eastern China.The precipitation days show a decreasing trend in most parts of China,with a rate of around–4.0 d per decade in central-eastern China,which reduces the sedimentation capacity of atmospheric pollutants.During the period of 1961–2012,the correlation coefficients between haze days and mean wind speed and strong wind days are mainly negative in central-eastern China,while there exists positive correlation between haze days and breeze days in the winter half-year.The mean wind speed and strong wind days are decreasing,while breeze days are increasing in most parts of China,which is benefitial to the reduction of the pollutants diffusion capacity.As a result,haze occurs more easily.

Precipitation changes in the mid-latitudes of the Chinese mainland during 1960–2014

Based on daily precipitation data from 163 meteorological stations, this study investigated precipitation changes in the mid-latitudes of the Chinese mainland（MCM） during 1960–2014 using the climatic trend coefficient, least-squared regression analysis, and a non-parametric Mann-Kendall test.According to the effects of the East Asian summer monsoon on the MCM and the climatic trend coefficient of annual precipitation during 1960–2014, we divided the MCM into the western MCM and eastern MCM. The western MCM was further divided into the western MCM1 and western MCM2 in terms of the effects of the East Asian summer monsoon. The main results were as follows：（1） During the last four decades of the 20^（th） century, the area-averaged annual precipitation presented a significant increasing trend in the western MCM, but there was a slight decreasing trend in the eastern MCM, where a seesaw pattern was apparent. However, in the 21^（st） century, the area-averaged annual precipitation displayed a significant increasing trend in both the western and eastern MCM.（2） The trend in area-averaged seasonal precipitation during 1960–2014 in the western MCM was consistent with that in the eastern MCM in winter and spring. However, the trend in area-averaged summer precipitation during1960–2014 displayed a seesaw pattern between the western and eastern MCM.（3） On an annual basis,both the trend in rainstorms and heavy rain displayed a seesaw pattern between the western and eastern MCM.（4） The precipitation intensity in rainstorms, heavy rain, and moderate rain made a greater contribution to changes in the total precipitation than precipitation frequency. The results of this study will improve our understanding of the trends and differences in precipitation changes in different areas of the MCM. This is not only useful for the management and mitigation of flood disasters, but is also beneficial to the protection of water resources across the MCM.