Zheng Jingyun

Meiyu in the middle and lower reaches of the Yangtze River since 1736

Abstract“Yu Xue Fen Cun” records during the Qing Dynasty are used to identify the starting and ending dates of Meiyu at the period of 1736–1911. These results, along with the instrumental meteorological records, are used to reconstruct the series of length and precipitation of Meiyu during 1736–2000 over the middle and lower reaches of the Yangtze River. The characteristics of Meiyu are analyzed since 1736. Moreover, the strength of East Asian Summer Monsoon and locations of rainband are discussed, based on the relationship between the length of Meiyu and the Index of East Asian Summer Monsoon. It is found that the starting and ending dates and the length of Meiyu have significant interannual and interdecadal variations. Apart from 7–8 years, 20–30 years and 40 years cycles for the lengths of Meiyu, the centennial oscillation is also presented. The length of Meiyu, monsoon rainband movement over eastern China, and the strength of East Asian Summer Monsoon (EASM) have a very good correlation, which can be expressed in the following: during the periods of 1736–1770, 1821–1870 and 1921–1970, the EASM was stronger, and the monsoon rainband was located in North China and South China easily, corresponding to the decreased length of Meiyu. Whereas during the periods of 1771–1820, 1871–1920 and 1971–2000, the EASM was weaker and monsoon rainband usually stopped at the middle and lower reaches of the Yangtze River, corresponding to the increased length of Meiyu.

The climate regionalization in China for 1981-2010

The scheme of climate regionalization in China was conducted by the classification criteria of temperature zone, arid/humid region and climatic sub-region, and the variables used in the criteria were calculated as mean values of the 30 years by using the daily meteorological data of 658 stations from 1981 to 2010. In the classification criteria, the temperature zones were classified by the general guideline of the days with daily temperature steady above 10℃, and the secondary guideline of January mean temperature, or by their referenced variables including the accumulated temperature with daily temperature steady above 10℃ and annual minimum temperature, respectively. The arid/humid regions were classified by the annual aridity index and annual precipitation amount in turn. The climatic sub-regions were classified by the July mean temperature. The result shows that China can be divided into 12 temperature zones, 24 arid/humid regions and 56 climatic sub-regions. Compared with the climate regionalization scheme for the period of 1951- 1980, several boundaries of temperature zones in eastern China shifted northward in 1981-2010 due to the climate warming. The east part of the northern boundary of warm temperate zone shifted more than 1.0° at a maximum. On average, the east part of the northern boundary of north subtropical zone shifted 1.0°. The middle part of the northern boundary of mid-subtropical zone shifted 2.0° at a maximum. The west part of the northern boundary of south subtropical zone shifted 0.5°-2.0°. In West China, the shift of temperature zone was not significant in horizontal due to the vertical landform. However, the plateau sub-cold zone was shrunk while the plateau temperate zone was enlarged in the Tibetan Plateau. Because precipitation decreased in North China, southeastern part of Northeast China and eastern part of Northwest China, the boundary of the semi-arid and sub-humid region in Northern China shifted eastward and southward, and in which, the boundary between 36°-41°N shifted 0.5°-2.5°at longitude. Moreover, the climate in the most of arid regions and semi-arid regions in Hexi Corridor, Xinjiang and the Tibetan Plateau changed to be more humid.

Recent advances on reconstruction of climate and extreme events in China for the past 2000 years

China is distinguished by a prominent monsoonal climate in the east of the country, a continental arid climate in the northwest and a highland cold climate on the Qinghai-Tibet Plateau. Because of the long history of Chinese civilization, there are abundant and well-dated documentary records for climate variation over the whole of the country as well as many natural archives (e.g., tree-rings, ice cores, stalagmites, varved lake sediments and corals) that enable high-resolution paleoclimatic reconstruction. In this paper, we review recent advances in the reconstruction of climate and extreme events over the last 2000 years in China. In the last 10 years, many new reconstructions, based on multi-proxies with wide spatial coverage, have been published in China. These reconstructions enable us to understand the characteristics of climate change across the country as well as the uncertainties of regional reconstructions. Synthesized reconstructed temperature results show that warm intervals over the last 2000 years occurred in AD 1–200, AD 551–760, AD 951–1320, and after AD 1921, and also show that cold intervals were in AD 201–350, AD 441–530, AD 781–950, and AD 1321–1920. Extreme cold winters, seen between 1500 and 1900, were more frequent than those after 1950. The intensity of regional heat waves, in the context of recent global warming, may not in fact exceed natural climate variability seen over the last 2000 years. In the eastern monsoonal region of China, decadal, multi-decadal and centennial oscillations are seen in rainfall variability. While the ensemble mean for drought/flood spatial patterns across all cold periods shows a meridional distribution, there is a tri-pole pattern with respect to droughts south of 25°N, floods between 25° and 30°N, and droughts north of 30°N for all warm periods. Data show that extreme drought events were most frequent in the periods AD 301–400, AD 751–800, AD 1051–1150, AD 1501–1550, and AD 1601–1650, while extreme flood events were frequent in the periods AD 101–150, AD 251–300, AD 951–1000, AD 1701–1750, AD 1801–1850, and AD 1901–1950. Between AD 1551–1600, extreme droughts and flood events occurred frequently. In arid northwest China, climate was characterized by dry conditions in AD 1000–1350, wet conditions in AD 1500–1850, and has tended to be wet over recent decades. On the northeastern Qinghai-Tibet Plateau, centennial-scale oscillations in precipitation have occurred over the last 1000 years, interrupted by several multi-decadal-scale severe drought events. Of these, the most severe were in the 1480s and 1710s. In southwest China, extreme droughts as severe as those seen in Sichuan and Chongqing in 2006 are known to have occurred during historical times.

Drought/flood spatial patterns in centennial cold and warm periods of the past 2000 years over eastern China

Drought/flood spatial patterns over eastern China under centennial cold and warm regimes were investigated. The 63-site yearly dry/wet grade data set derived from Chinese historical documents was used, together with an up-to-date 2000-year long temperature series reconstructed from synthesis of 28 temperature proxies in China. We defined the index of difference between drought and flood frequency to reconstruct the drought/flood spatial patterns for five cold periods (440-540, 780-920, 1390-1460, 1600-1700, and 1800-1900 CE) and four warm periods (650-750, 1000-1100, 1190-1290, and 1900-2000 CE). The results showed that there are no consistent patterns over eastern China among all cold/warm periods. However, for most warm periods, drought (flood) dominated north (south) of the Yangtze River. The ensemble mean drought/flood spatial patterns for all warm periods illustrated a dipole pattern with drought (south of 25°N)-flood (25°-30°N)-drought (north of 30°N), with the exception of flood in the Loess Plateau. For all cold periods, the ensemble mean drought/flood spatial patterns showed an east to west distribution, with flood east of 115°E and drought dominant west of 115°E, with the exception of flood between approximately110°E and 105°E. These differences in ensemble mean drought/flood patterns suggest that the probability of drought north of the Yangtze River and flood in the valleys of the XiangJiang and GanJiang rivers south of the Yangtze River is higher in warm periods than in cold periods.

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 El-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 El-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 El-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.

Reconstruction of Temperature series in China for the last 5000 Years

A temperature series with a 100 year resolution for the last 5000 years in China has been reconstructed by using 31 longterm temperature proxy series selected from recent publications in the last 20 years. The proxy records include pollens, stalagmites, lake-sediments, peat, ice cores and historical documents. The result reveals that in the millennial scale temperature variation it was warm in 3050-250 BC and it was cold in 250 BC-1950 AD. In the above two periods there were many stages of sub-scale temperature fluctuations. The result also shows an obvious temperature discrepancy on the century to multi-century scale between the Eastern Monsoon Region, the Qinghai-Tibet Region and the Northwestern Region in 2850 BC, 2350 BC, 1350 BC, 950-350 BC, 50-250 AD, and 550 AD. A comparison between the reconstructed series of this paper and some North Hemisphere temperature series indicates that in the longterm scale change, the temperature change in China is in phrase with that of the Northern Hemisphere during the last 5000 years, while on the century to multi-century scale there are differences at the beginning and end times, which may imply that temperature change does not occur simultaneously in different regions.

ANALYSIS OF DRIVING FORCES ON THE CHANGE OF HISTORICAL FARMLAND USE IN SHANDONG PROVINCE DURING THE QING DYNASTY (1644-1911)

How land-cover has been changed by human use over the last 300 years is one of the five overarching questions guiding the Land-use/Cover Change (LUCC) Science/Research Plan. China has variety of historical documents providing unique data superiority. So the characteristics of farmaland area in Shandong Province during the Qing Dynasty (1644–1911) are summarized firstly: 1) the rising trend of farmland area was striking; 2) farmland area had remarkable fluctuation; 3) farmland area per capita decreased dramatically; 4) wasteland reclamation index increased rapidly. Then, the driving forces of farmland area change are analyzed. It is concluded that natural and human factors are jointly influential. Among the driving forces, human dimensions are the main factors of farmland area change, which direct the general tendency of the changes mentioned above. And the natural factors influence the stability of farmland area as well. Variation of the natural factors would act as the major contributory factor to farmland area change during years or periods of abrupt climatic changes, or during the intensive occurring periods of natural hazards. Besides, the passive aspects of human factors, such as war chaos also influenced the fluctuation of the farmland area. This research indicates that it is feasible to study the land-use/cover change by Chinese historical literatures, which has huge potential to provide a comprehensive picture of the growing dominance of human land-use and land-cover patterns that can be used in many global change research projects.

Dryness and wetness variations for the past 1000 years in Guanzhong Plain

In this study, spatial-temporal statistical technologies were utilized to interpolate a dryness and wetness grade dataset, which was reconstructed from previous Chinese historical documents, but with significant data gaps in the past 1000 years, and a complete grade dataset of dryness and wetness was developed for Guanzhong Plain including seven sites at Linfen, Changzhi, Xi’an, Fengxiang, Luoyang, Nanyang and Hanzhong. The probit model was used to interpolate the missing values at the spatial scale depending on the highest variance explanation between neighbouring stations, and the Markov chain model was used to interpolate the temporal series depending on the known features of the dataset from 1470 to 2010. On the basis of this dataset, long-term variation features and extreme drought and flood events in the Guanzhong Plain were identified. By means of wavelet analysis and ensemble empirical mode decomposition methods, the main cycles of interannual-interdecadal-centennial scales of dryness and wetness variations were detected and the relationships between periodicity and driving forces were analyzed. Results indicated that the dry-wet change of the Guanzhong Plain has had three stages in the past 1000 years, that is, the climate changed from wet to dry in 960–1150, then from dry to wet in 1151–1800, and again from wet to dry after 1801. On the half-centennial time scale, five wet periods in 960–1000, 1151–1200, 1251–1300, 1351–1400 and 1651–1900, and five dry periods in 1001–1150, 1201–1250, 1301–1350, 1401–1650 and after 1901 were identified. Extreme drought and flood events occurred with high frequency in the 17th and 19th–20th centuries, about once every two years. Extreme drought events lasting 5 years occurred in 1070–1089, 1212–1216, 1327–1331, 1431–1445, 1481–1491, 1634–1641, 1688–1692, 1714–1722, 1875–1878, 1925–1931 and 1993–1997. Extreme flood events lasting 5 years occurred in 981–985, 1647–1653, 1658–1664, 1676–1680, 1725–1730, 1848–1854 and 1882–1889. The dry-wet changes of the Guanzhong Plain has an inter-annual oscillation with a 3–7-year scale, inter-decadal oscillations with quasi-10-year, quasi-30-year and quasi-70-year scales and a centennial oscillation with a quasi-100-year scale. The climate of Guanzhong Plain tends to be drier than in a normal year in the year of the occurrence of the El Nino or the following year. On the quasi-70-year scale, the correlation of the Pacific Decadal Oscillations and the dry-wet change shows a positive (negative) relationship before (after) 1435, which suggested that the relationship between them is not stable in the long term. In addition, the solar maximum corresponds to the dry climate. It is worth noting that due to the lack of long climate series, both reconstruction and model simulation approaches are used to study climate change during historical times. The reconstructed dryness and wetness variations for the past 1000 years in Guanzhong Plain may still lack certainty, and in the future, further analyses and comparisons between the reconstructions and simulations need to be conducted, in order to diagnose the dynamic mechanisms of the climate features in Guanzhong Plain.

The urban land area Change in China from 1820 to 1999

According to the length of city perimeter and the administration systems recorded in the historical literatures of the Qing Dynasty, a set of methods is developed to convert the historical records into the area of urban land use, by which a set of preliminary estimated urban land use data of the 18 provinces during the Emperor Jiaqing (1820AD) in the Qing Dynasty, is achieved. Based on the above achievements, the regional differences of urban land use are analyzed, and the comparison in urban land use between the Qing Dynasty and present (1999) is made.