Reconstruction of the starting time series of rainy season in Yunnan and the evolvement of summer monsoon during 1711-1982

According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yunnan during 1711-1982 has been reconstructed. The analysis indicates that there are obvious fluctuations in the starting date of the rainy seasons in Yunnan in a year or years, and long fluctuation on the decadal scale. The rainy season comes earlier in the early 18th century, later in the 19th century and earlier again in the 20th century. This reflects to a certain degree the gradual change of the summer monsoon in Yunnan. There exists an obvious quasi-3 years cycle, which is related to EI-Nino＇s quasi-3 years cycle, and a 11.3-year cycle which is notably related to the 11-year cycle of the solar activity of starting date of the rainy seasons in Yunnan. Meanwhile, the dissertation finds that the EI-Nino is very important to the starting date of the rainy seasons in Yunnan. The starting date of the rainy seasons in Yunnan often comes later or normally in the year of EI-Nino. However, there is an obvious imperfect period in such influence, which in turn may mean that there is a certain fluctuation in the effect of ENSO on Asian summer monsoon.

Variations of the thermal growing season during the period 1961–2015 in northern China

Researching into changes in thermal growing season has been one of the most important scientific issues in studies of the impact of global climate change on terrestrial ecosystems. However, few studies investigated the differences under various definitions of thermal growing season and compared the trends of thermal growing season in different parts of China. Based on the daily mean air temperatures collected from 877 meteorological stations over northern China from 1961 to 2015, we investigated the variations of the thermal growing season parameters including the onset, ending and duration of the growing season using the methods of differential analysis, trend analysis, comparative analysis, and Kriging interpolation technique. Results indicate that the differences of the maximum values of those indices for the thermal growing season were significant, while they were insignificant for the mean values. For indices with the same length of the spells exceeding 5°C, frost criterion had a significant effect on the differences of the maximum values. The differences of the mean values between frost and non-frost indices were also slight, even smaller than those from the different lengths of the spells. Temporally, the starting date of the thermal growing season advanced by 10.0–11.0 days, while the ending dates delayed by 5.0–6.0 days during the period 1961–2015. Consequently, the duration of the thermal growing season was prolonged 15.0–16.0 days. Spatially, the advanced onset of the thermal growing season occurred in the southwestern, eastern, and northeastern parts of northern China, whereas the delayed ending of the thermal growing season appeared in the western part, and the length of the thermal growing season was prolonged significantly in the vast majority of northern China. The trend values of the thermal growing season were affected by altitude. The magnitude of the earlier onset of the thermal growing season decreased, and that of the later ending increased rapidly as the altitude increased, causing the magnitude of the prolonged growing season increased correspondingly. Comparing the applicability of selected indices and considering the impacts of frost on the definitions are important and necessary for determining the timing and length of the thermal growing season in northern China.

Characterizing Spatial Patterns of Phenology in Cropland of China Based on Remotely Sensed Data

This study used time-series of global inventory modeling and mapping studies （GIMMS） normalized difference vegetation index （NDVI） datasets at a spatial resolution of 8 km and 15-d interval to investigate the spatial patterns of cropland phenology in China. A smoothing algorithm based on an asymmetric Gaussian function was first performed on NDVI dataset to minimize the effects of anomalous values caused by atmospheric haze and cloud contamination. Subsequent processing for identifying cropping systems and extracting phenological parameters, the starting date of growing season （SGS） and the ending date of growing season （EGS） was based on the smoothed NVDI time-series data. The results showed that the cropping systems in China became complex as moving from north to south of China. Under these cropping systems, the SGS and EGS for the first growing season varied largely over space, and those regions with multiple cropping systems generally presented a significant advanced SGS and EGS than the regions with single cropping patterns. On the contrary, the phenological events of the second growing season including both the SGS and EGS showed little difference between regions. The spatial patterns of cropping systems and phenology in Chinese cropland were highly related to the geophysical environmental factors. Several anthropogenic factors, such as crop variety, cultivation levels, irrigation, and fertilizers, could profoundly influence crop phenological status. How to discriminate the impacts of biophysical forces and anthropogenic drivers on phenological events of cultivation remains a great challenge for further studies.

Variations in the starting date of the pre-summer rainy season in South China, 1736-2010

The starting dates of the pre-summer rainy season during historical times （1736- 1911） in Fuzhou and Guangzhou of South China, were determined and reconstructed on the basis of historical documents in the Yu-Xue-Fen-Cun archive, together with observed features of precipitation during the pre-summer rainy season. In addition, starting dates of the pre-summer rainy season from 1953 in Fuzhou and from 1952 in Guangzhou were reconstructed for the instrumental period. These data allowed for analyses of inter-annual and inter-decadal changes in the starting dates of the pre-summer rainy season in South China over the past 300 years. Results show that the mean starting date of the pre-summer rainy season in South China was the first pentad of May; in addition, periodicities in the starting dates of 2-3 years, 10 years, and 40 years were detected during the period 1736-1911, and of 2-3 years, 10 years, and 22 years during the instrumental period. From 1736 to 1911, the earliest starting dates at Fuzhou and Guangzhou both occurred at the fourth pentad of April, while the latest starting dates were at the sixth pentad of May in Fuzhou and the first pentad of June in Guangzhou. During the instrumental period, the earliest and latest starting dates were at the fourth pentad of April and the first pentad of June, respectively, in both Fuzhou during 1953-2010 and Guangzhou during 1952-2010. The maximum difference between neighboring decades during 1736-1911 was 2.2 and 1.6 pentads in Fuzhou and Guangzhou, respectively, and during the instrumental period it was 2.5 and 2.4 pentads in Fuzhou and Guangzhou, respectively.