Defined Reversal of the Wind Directions Between Sum- Mer and Winter. In

February 1992 P. K. Wang 423

Recent Studies of the Reconstruction of East Asian Monsoon

Climate in the Past Using Historical Literature of China

By Pao K. Wang

Department of Meteorology, University of Wisconsin, Madison, WI 53706, U.S. A.

and

De'er Zhang

Academy of Meteorological Science, State Meteorological Administration, Beijing, People's Republic of China (Manuscript received 5 August 1991, in revised form 7 December 1991)

Abstract

Recent work on the reconstruction of past climate of the part of China that is influenced by the East Asian monsoon based on Chinese historical literature are reviewed. General climate information that can be extracted from historical documents are described and some examples are given. The sources of available documents useful for more quantitative reconstruction purposes are given and assessed. Reconstruction of winter and summer temperature series and dryness/wetness series are then reviewed and discussed. The reconstruction of temperature series were generally based on climatological interpretation of phenological records such as the dates of lake or river freezing, bird migration, or the beginning and ending of snow. Reconstructed temperature series for various parts of China are given. Next, the reconstruction of humidity series are reviewed. The data sources for this purpose are mainly flood, drought, and rain records. Some high quality data sources, such as the daily weather reports, the Clear and Rain Records of Qing Dynasty, are also discusses. The reconstructed series are then used to summarize the general evolution of the monsoon climate of China from 300 to 1900 AD. A brief conclusion is made.

1. Introduction defined reversal of the wind directions between summer and winter. Monsoon phenomenon is the central feature of the In this paper, we will summarize recent studies on climate in East Asia and it has been recognized by the reconstruction of past monsoon climate in East ancient people of this area for a long time. Be- Asia based on the historical documents of China. cause of the relatively early civilization of this area, The referencesare drawn mostly from the work done many monsoon-related weather and climate records by Chinese researchers. It would have been ben- are kept in written documents such as chronicles, eficial to include the work done by researchers in city, county, and provincial records, memoirs to the the neighboring countries such as Japan and Korea. throne, travel reports, agricultural books, private di- Unfortunately, the limitation of time has prevented aries, etc. (for example, Zhu, 1973; Wadachi, 1958; such an effort. Yoshino, 1978, 1981; Wang, 1979, 1980; Kim and In the succeeding sections, we will first review Choi, 1987; Wang and Zhang, 1988). Since mon- some general features of the records containing monsoon plays such a dominant role, virtually all climate soon climate information in historical documents. records in the ancient literature of China, Japan, The use of them to extract quantitative informa- Korea, and other countries in this region can be con- tion of climate will be briefly described. Then, a sidered as reflecting the monsoon influence. In this relatively detailed review of the research on the re- review, we shall take this broad interpretation of construction of past climate based on these records monsoon climate. However, sometimes we shall re- will be given. The reconstruction was usually fer the monsoon phenomenon as the more narrowly done either for the temperature or humidity (dry- (c)1992, Meteorological Society of Japan ness/wetness) series, although some other climatic

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Fig. 1. A map of China showing the geographical locations mentioned in the text.

parameters such as wind and the positions of pres- northeastward to Guangzhou.1 The above passage sure centers can also be deduced in some cases. Fi- indicates that the winter monsoon in Indian Ocean nally, the findings of these studies will be summa- then was NE so that the ship sailed to the SW. Sec- rized. ondly, his 5 month stay in Java was apparently not 2. Monsoon climate records in Chinese his- sightseeing but for the purpose of waiting for the torical literature SW summer monsoon to return to Guangzhou (Zhu, 1954). ,2.1 General literature related to monsoon The trade between China and Arab countries be- One of the earliest records in China concerned came more frequent in Song (960-1287 AD) and directly with monsoon was that written by Bud- Yuan (1280-1368AD) Dynasties. Such trades were dhist monk, Faxian, of East Jin Dynasty (317-419 accomplished mainly via oceanic routes which must AD) who traveled from today's Xian (the ancient have depended heavily on monsoon and there were Changan, the the Capital of China) to India by land reports saying that the foreign merchants usually in 399 AD but returned via an oceanic route fifteen arrived at China sometimes after the summer sol- years later. He reported on his return trip: "Sail- stice (in June) and went back to their countries in ing southeastward on the sea, we were helped by the "10th Month" around November). The timing the early winter trade wind and arrived at the Lion was obviously coincident with the change of mon- Country (i. e., today's Sri Lanka) in 14 days and soon wind direction. nights." He stayed in Sri Lanka for another 2 years Associated with the summer monsoon in East and eventually went to Java and stayed there for 5 Asia is the rainy season called Meiyu in China and months. Then, on "4th Month, 16th Day" (around Baiu in Japan, both meaning "plum rain," as the

May in the Gregorian calendar), he boarded a large 1 A map indicating the location of places mentioned in this ship along with other 200 some passengers and sailed paper is given in Fig. 1.

,294 February 1992 P. K. Wang 425 season coincides with the time when plum ripens. general contents of these documents. Some descrip- The plum rain is closely related to the SE mon- tions were also given by Wang (1979, 1980), Wang soon and for this reason the SE monsoon had been and Chu (1982), and Wang and Zhang (1988). called "drop plum wind" in Interpretation of Cus- The most well known source of historical climate toms (Feng Su Tong, by Ying Shao, circa 200 AD). records is the official dynastic histories of China. The famous Song poet, Su Shi (1036-1101 AD), These histories were normally (although no always) wrote an introduction to his poem Ship Wind say- written by officially appointed scholars of the dy- ing, "After the Meiyu has passed in Wu (around nasty succeeding the previous one. For example, Suzhou) area, there would be refreshing wind for the scholars of Yuan Dynasty wrote the OfficialHis- tens of days. It occurs every year. Local folks tory of the Song Dynasty. The materials used for call it the ship wind. This is also the time when these histories were that compiled by imperial his- seafaring ships return and the wind comes at the torians of the previous dynasty. The format of these same time with the ships." A Ming Dynasty book, histories are almost unchanged ever since Ban Gu Chats of Yuzhi Hall (Yuzhi Tang Tan Hui, edited (32-92 AD) wrote the History of Han. In addi- by Gu Mie and Xu Yingqiu), gave the SE monsoon tion to political events, most of these histories also another name: "In the 6th Month in the south there contain records of weather and climate. As a rule, are long southeast winds called the yellow sparrow only unusual phenomena or severe conditions were wind." Though the names are different, they all refer recorded. These records are usually found in either to the SE monsoon. the Book of Five Elements (Wuxing Zhi in Chinese Monsoon climate is known for its large spatial and pronunciation in pinyin system) or Book of Por- temporal variabilities. For example, the Meiyu rain- tents (Zaiyi Zhi) of each history. Occasionally, the fall can vary greatly from one year to the other. calamities were so severethat they became the steer- This too can be seen in ancient literature. For ing force of the political course of the country and example, a Song poet Sima Guang (1019-1086) therefore were recorded in the Biographies (Ben Ji, wrote in one of his poems that "In the yellow Shi Jia, or Lie Zhuan). plum season/Rains in every family." Another poet, The recognized official histories are the so-called Zeng Yu (1073-1135), also of Song, wrote, "When Twenty Four Histories which include a series of plums turn yellow/Every day is sunny." Yet another books starting with Shi Zi ( The Book of History) Song poet, Dai Fugu (1167-?), wrote, "Ripen plum by Sima Qian (145-86 BC) and Han Shu by Ban weather/Half sunny, half cloudy." (one of the easiest Gu down to the History of Ming Dynasty. Reprints sources to find these poems is the Poems of Thou- of these histories are widely available commer- sand Scholars (Qian Jia Shi)). All three observa- cially. The History of Qing Dynasty (1644-1911 tions are still valid today in general. AD) has not been published but a draft version Due to such large variabilities, flood and drought Qing Shi Gao, is commercially available. In addi- are not unusual in the monsoon climate zone in tion, a pre-Han Dynasty chronicle, the BambooAl- China. There are folklores that associate flood and bum (Zhu Shu Ji Nian), is also considered as having drought to monsoon. One example is given in Folk- the status of an officialhistory. lores of Farmers (said to be written by Tsui Shi of The relevant weather and climate records in these Han Dynasty, but quoted by Tao Zungyi (circa 1400 histories consist of flood, drought, excessiverain, un- AD) of Ming in his book Suo Hu): "When ship wind usual cold and hot weather, severe wind or thun- and clouds arise/The Drought Demon is immensely derstorms, dust rains, excessive snow, and heavy happy." This lore associates the SE monsoon with hailstorms. There are also other records such as drought condition. Zhu (1954) explained this rela- the dates of lake or river freezing, arrival of mi- tion in terms of the influence between the Pacific grating birds, blossom of certain flowers, records Subtropical High. of harvest, grain prices, famine or harvest, and lo- There are also many other records which can cust infestation that could reflect the climatic con- be used to qualitatively understand monsoon phe- ditions indirectly. Figure 2 shows an example of the nomenon in historical time. Some information is weather records (Hail Damages) in the History of given in Zhu (1979) and Zhu and Yuan (1973). Song Dynasty. Some examples of the weather and climate records are translated into English by Wang 2.2 Historical records for quantitative monsoon studies (1979). The records in earlier dynasties normally have In addition to the qualitative materials that we time resolution of about a year. Sometimes a res- described above, there are many more materials in olution of a season is also possible. The records in Chinese historical documents that can serve as data later dynasties often have time resolution as good as sources from which quantitative information of past a day. monsoon activities can be retrieved. It is the pur- The major advantage of the climatic information pose of this section to briefly describe the nature and extracted from the officialhistories is in the quality

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nasty, it became more abundantly available after that. The time resolution of climatic information from local records is usually from one seas to one year, although occasionally a resolution of one day is also possible for some places. The contents of the entries related to climate are similar to that in the official histories. Recently, the flood and drought entries in these records had been combed through carefully and compiled and a Yearly Charts of Dry- ness/Wetness in China for the Last 500 YearPeriod (Academy of Meteorological Science, 1983, hence- forth called the Yearly Charts) was published. Nu- merous studies of the climatic changes in China in the last 500 years were performed based on this extensive data set. The main advantage of this data set is the coveragewhich essentially covers the whole of China, although the records for the eastern half of China are much more complete than the western half due to historical reasons. Since the data were derived from collections of local records, the quality of observation and the uniformity of the data sets are probably not as high as that of the official histories, considering that the observers and reporters were not professionally trained. Because of the importance of weather and climate to agriculture, which was the main economy of China in the past 2,000 (perhaps even 3,000) years, the emperors often paid great attention to them and sometimes demanded special weather reports from local officials. One of these special reports is the Clear and Rain Records (Qing-yu-lu) Fig. 2. A page of The History of Song Dynasty which are daily weather reports in the Qing (1643- (typeset in 1345 AD) depicting hailstorms 1911) Dynasty (Wang and Zhang, 1988). These re- and thunderstorms. ports were compiled by local officialsand submitted to the emperor on a monthly basis. An entry in of observation. The main reason is that observations these reports includes the year, month, day, and the were made by government officials who were trained weather conditions. The weather conditions include systematically and were reported regularly. Obser- sky conditions (overcast, clear, fog, or rain), wind vations made by private sources were more sporadic directions (N, S, E, W, NE, SE, NW, SW) precip- and of nonuniform technical quality. The disadvan- itation types (such as rain, snow, light rain, light tage is in the coverage-records from official histories snow, heavy rain, heavy snow, thunderstorms, etc.), were mostly events occurred at or near the national and duration (start and ending hours). The time capitals. Other locations were covered only occa- resolution is one hour. Figure 3 shows an example sionally. For a wider coverage, we must turn to other of the Clear and Rain Records of Nanjing in May sources. 1724. For more detailed descriptions of the contents Despite their limitations, the official records have of the Clear and Rain Records, see Wang and Zhang been used for long term climatic studies. For exam- (1988). ple, Wang (1980) used the records of winter thunder- Although the Clear and Rain Records are cer- storms in official histories of China to study the long tainly one of the best ancient non-instrumental term variations of the electrical climate of China. weather reports available, many are already lost. Of More examples will be discussed in later sections. the remaining records known so far, only those of Local records (Fang Zhi) form another important Beijing, Nanjing, Suzhou, and Hangzhou are com- category of documents from which weather and cli- plete enough to warrant analysis. Beijing's records mate information can be extracted. There are re- are the longest, being from 1724 to 1903. The portedly more than 7,000 volumes of these records lengths of another three sets of records are shorter (Hong and Chen, 1983). These include records and are limited to the 18th century only. There are of cities, counties, prefectures, and provinces. Al- Clear and Rain Records for another forty some cities though local records existed before the Ming Dy- but they are not continuous and only available for

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Fig. 3. The second half of the Clear and Rain Records of Nanjing in May, 1724.

Fig. 5. A snow record contained in a memoir to the throne.

There is another kind of weather record in the Qing Dynasty that is potentially useful for retrieval of precipitation in the historical time. This is the Inches of Rain and Snow (Yu-xue-feng-cun). Unlike the Clear and Rain Records, these are strictly precipitation records. Figure 4 shows an example of snow records. The snow depth in this report refers to the depth above ground. The precipitation reports were sometimes combined with the memoirs to the throne and an example is shown in Fig. 5. Fig. 4. An example of the Inches of Rain and Note that the number of inches of rain reported in Snow. Fig. 5 refers to the depth of soil seeped through by rain water and is often called "underground inches." very short periods (e. g., a few months). The Clear This set of data covers a wider area than the Clear and Rain Records of Beijing, Nanjing, Suzhou and and Rain Records and is currently being compiled. Hangzhou have been analyzed and will be discussed More details of the Inches of Rain and Snow can be later2 (see, for example, Zhang and Wang, 1989, found in Wang and Zhang (1988). 1991; Wang and Zhang, 1991). The documents mentioned above were compiled or archived by either the imperial or local govern- 2 The computer -coded data sets of the Clear and Rain ment. There are also private sources that contain Records and the reconstructed monthly precipitation series weather and climate information. The best of these of Nanjing, Suzhou, and Hangzhou for the months of May- August have been completed. Researchers interested in these are the diaries. Many of the existing diaries contain data should contact the authors of this paper. daily weather information, although not as detailed

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lies reflects mainly the change in the anticyclonic system and hence the winter monsoon circulation. However, it has been recently realized that in order to understand the change in summer monsoon circulation, it is necessary to reconstruct the summer temperature series. The fluctuation of summer temperature anomaly, together with the summer precipitation fluctuation, reflect the change in the western North Pacific Subtropical High which is a dominant factor of the summer weather in China. Thus, the reconstruction of summer temperature series is now receiving increasing attention. In the following, we shall review first the reconstruction of winter temperature series. The review of the summer temperature series will then follow. 3.1. Reconstruction of winter temperature series Due to the lack of thermometers, no direct temperature series were available for China before 1891. Thus all temperature series were reconstructed from the inference of other climatic indicators. In this section, we will review the reconstruction of winter temperature series in China. Some studies pertain to the averaged conditions in China. Others pertain Fig. 6. A page of Zeng Guofan's diary. to specific regions. Zhu (1973) studied the climatic change of China as that in the Clear and Rain Records. Figure 6 in the last 5,000 years by using a wide assortment shows a page of the diary written by Zeng Guofan of data sources, mostly documentary. These sources (1811-1872AD), a well known scholar-generalof the included entries in official histories, local records, Qing Dynasty. There are numerous other diaries some diaries, and even ancient poems. To obtain similar to this that can be used for retrieval of past information for the very early periods (such as the climate information. Gong et al. (1983) have used Shang Dynasty and beyond), fossil and oracle bone some diaries to reconstruct past climate of China. data were used. The main emphasis of his study was on the fluctuation of winter temperature of China as 3. Reconstruction of temperature series a whole. based on historical documents Most of the natural phenomena considered by Zhu In this section, various studies concerned with the as climatic indicators are phenological such as the reconstruction of the climate of China in histori- freezing dates of lakes and rivers, starting and end- cal time are reviewed. The time spans of climate ing dates of snow and frost, arrival dates of swallow, covered by these studies vary greatly; some for sev- blossoming dates of flowers, distribution of bamboo eral thousand years, others a few decades. Most forests and plum trees, etc. Variations of these in- of the reconstruction work focused on either the dicators in time thus represent climatic change. For warm/cold conditions or the humidity conditions. example, the frequent reports of "no snow," "no ice" The former are often expressed in terms of temper- in the Histories of Sui and Tang Dynasty (589-907 ature anomaly series whereas the latter are often ex- AD) can be interpreted as having relatively warm pressed in terms of precipitation or wetness/dryness winters. There are also supporting evidence of this anomaly series. interpretation such as the planting of citrus trees in It is well known that temperature distributions the then national capital, Changan (today's Xian). have higher spatial uniformity than precipitation in It is impossible to grow citrus trees in that area un- East Asian monsoon climate zone. Furthermore, der the present climatic condition. Thus he con- winter temperatures have higher regional uniformity cluded that the winter temperatures during the Sui than summer temperatures. Thus winter tempera- and Tang Dynasties were higher than present. On ture anomaly is often taken as the indicator of the the other hand, the citrus trees in Lake Taihu area climatic change of China (Zhu, 1973). Consequently, in the Lower Yangtze region were completely wiped most temperature series reconstructed were those in out by the extremely cold winter in 1111 AD in the winter time. Since the winter weather at the surface Southern Song Dynasty. The reports of extended level in China is largely influenced by the Siberian periods of snow during this time tend to support High, the fluctuation in winter temperature anoma- this interpretation. Zhu (1973) estimated that the

298 February 1992 P. K. Wang 429

In addition, since the numbers in this curve were derived from phenological interpretation, as opposed to instrumental records, relatively large error bars should be attached to them. Nevertheless, it it be- lieved that the curve shows a realistic relative fluctuation of winter temperature. A study of the fluctuation of winter thunderstorm frequency in China by Wang (1980), although not a proof of the above conclusion, shows at least that the temperature fluctuation curve was derived from consistent data sources. Winter thunderstorm is rare in China and was considered as a bad omen when it occurred. As such, it was the imperial astronomer/historian's duty to write it down in records. Thus the records of winter thunderstorms would be relatively complete as compared to that occurring in summer which was considered as normal. Wang's data were compiled completely from the officialhistories. Instead of counting the total number of winter thunderstorm reports, the number of years with thunderstorm in a certain interval (say, 30-years) was determined. Since most records per- tained to the condition in the national capital, this Fig. 7. Temperature fluctuations of China data set is relatively similar to the temperature data (Zhu, 1973). set obtained by Zhu (1973). Figure 8 shows the comparison of these two series. It is seen that the temperature of Hangzhou (30.15N, 120.10E) in April two have a substantial negative correlation with a in the 12th century was about 1-2°C lower than coefficient of r=0.68±0.05. This correlation coef- present based on the delayed ending dates of snow ficient may not seem very high. It is very signifi- then. cant, however, considering the completely different Figure 7 shows the results obtained by Zhu (1973). nature of the two series. Unlike Zhu's series which The fluctuations of the temperature over time is depends on the interpretation of qualitative pheno- clear. For example, there was an extended warm logical descriptions, the winter thunderstorm series period from 7th to the middle of the the 11th cen- was constructed based on quantitative counting of tury relatively warm in China. Although the curve the events. Thus, we can say, at least, that the data is supposed to represent the average condition of sources used by these two studies would provide con- China, we have to remember that each data point sistent pictures of climatic change. was actually derived from only a few (and most fre- The negative correlation of the two series says quently, just one-usually the national capital) sta- that the colder the climate, the more likely winter tions. Naturally, we have to use discrimination when thunderstorm would occur in China. Since winter we apply this conclusion to any individual station. thunderstorms in China are essentially frontal, this

Fig. 8. Comparison of temperature fluctuations and winter thunderstorm frequency variation in China (Wang, 1980).

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Fig. 9. Frequency of dustfall (in 10-year interval) in China (Zhang, 1984). Dashed curve is the 10-year moving average.

Fig. 10. Frequency of cold winters (in 10-year interval) in China (Zhang and Gong, 1979). C. P. stands for "cold period" .

would indicate that frontal activity would be general. This latter fact will be discussed in a later stronger in colder climate. This clearly had to be section. For now, this indicates that the dustfall a result of the change in the winter monsoonal cir- events should be more frequent during drier periods culation in East Asia in the cold years, although it which seems to make intuitive sense. is not clear yet what the changes were. Frequent dustfall would mean a relatively turbid Zhang (1984) presented an analysis of the 1156 atmosphere which tends to scatter more solar radi- dustfall records compiled from official histories, lo- ation back to space and hence results in a cooler cal records, private notes, etc., excluding those due climate, similar to the effect of volcanic eruption to volcanic eruptions and local dust storms. It is (see, for example, Lamb, 1972; Bryson, 1989). How- known that dustfall is more frequent in northern ever, it cannot be said here that the correspondence China where climate is drier. This was also true in of cold climate with frequent dustfall indicates any the historical time, as Zhang's study shows. But the cause-and-effect relation. But there might be an in- frequency distribution is used to represent the aver- fluence of the latter on the former although the de- age condition over the whole country as the studies gree of which is unknown. of Zhu (1973) and Wang (1980). The time series of Zhang and Gong (1979) studied the frequency dustfall is shown in Fig. 9. Again, it is seen that the of cold winters using information in local records, pattern looks very similar to the two curves in Fig. 8, notes, and diaries. Figure 10 shows the decadal fre- once more confirming the consistency of the histori- quency of cold winters compiled from them. It is cal documents. Here we see that dustfall events were seen that, compared to 17th and 19th centuries, the more frequent during colder periods. A comparison climate of the 18th century was relatively warm. Be- of the dustfall series with the moisture index series cause the winter temperature at a specific location of eastern China by Zheng et al. (1986) revealed that depends primarily on the temperatures of the cold the colder periods corresponded to drier periods in air masses entering China and the routes they take,

300 February 1992 P. K. Wang 431 it is possible to trace back the motion of the cold were fairly synchronous, especially in the long wave air masses by examining the spatial variation of the components (170-190 year cycles). cold winter frequency distribution. This was done Gong et al. (1983) used the snowfall probability of by Zhang and Gong (1979) who determined that in Nanjing, Suzhou, and Hangzhou in the 18th century the warmer periods (1551-1600, 1721-1830, 1901- to study the winter temperature fluctuation in the 1950) the cold air frequency moved along the east- Lower Yangtze reaches. They first obtained a set ern routes (east of 115°E) while in colder periods of regression relations between the temperature and (1500-1550, 1601-1720, 1830-1900) they took more snowfall probability using modern data sets. Then frequently the western routes (west of 115°E). Po- they applied these relations to regress winter tem- tentially this knowledge, when coupled with other perature series of these three stations in the 18th knowledge (such as the pattern of precipitation and century using the snowfall probability determined wind direction), will allow the determination of win- from the respective Clear and Rain Records. They ter monsoon circulations in East Asia during these concluded that the mean winter (Dec. -Feb.) tem- years. perature at the Lower Yangtze reaches was about The length of the growing season of crops is also 1.0°C (for Suzhou and Hangzhou) to 1.5°C (Nan- an indicator of climate, especially the temperature jing) lower than present. But the spring (Mar.- condition. Gong and Chen (1980) studied the vari- May) mean temperature was somewhat warmer ation of the length of growing season of some crops. than present, according to their analysis based on One of the interesting facts mentioned by them was records in some private notes and diaries. the experiment of planting rice in two seasons in They also analyzed the wind direction series of Jiangsu Province in the 18th century. Such practice Hangzhou from the Clear and Rain Records and was done before in the 5th and 8th centuries. The found that the NW wind frequency in Nov-Jan experiment was conducted by an official named Li Xi in the 18th century was about 10% higher than initially in Suzhou area and was gradually expanded present, while the NE wind frequency in spring and to other areas in the province. However, it had to summer was also higher than present. The more be abandoned in the 19th century due to the colder frequent NE winds would imply a more humid cli- climate. Unaware of the climatic effect, Li Xi re- mate. This point will be further discussed in a later ported in a memoir to the emperor that the success section. in the 5th and 8th centuries was because "ancient 3.2 Reconstruction of summer temperature series farmers were smarter" but their techniques were un- As mentioned above, most of the studies were fortunately lost. mainly concerned with the winter situation. Sum- In an attempt of refine the spatial resolution, mer temperatures are subjected to higher spatial Zhang (1978, 1989) studied the winter temperature variability and it is more difficultto find a reliable in- of southern half of China (south of Qinling Moun- dicator. Recently, Zhang and Liu (1987) studied the tains and the Huai River, roughly bounded by 33°N, summer temperature variation of Beijing form 1724 98°E,and the coastline) in the last 5 centuries. The to 1903 by using the Clear and Rain Records. As data were compiled from local records and the Draft mentioned previously, the Clear and Rain Records of the History of the Qing Dynasty. The study are are mainly concerned with precipitation. However, was divided into 8 regions: (I) Lower Yangtze, (II) it is known that the correlation between the temper- Middle Yangtze, (III) Hunan and Jianxi Provinces, ature and number of precipitation days in Beijing (IV) Ming River and Ou River area (in Fujian is relatively good in summer, especially June and Province), (V) Tropical China (Southern Fujian, July where the coefficientswere -0.692 and -0.639, Guangdong, and Guangxi), (VI) Nanling Moun- respectively, in the period of 1951-1982. This is tains, (VII) Sichuan and Guizhou Provinces, and presumably due to two factors: (1) the cloudy sky (VIII) Northern Yunnan Province. A year was de- in a rainy day reduces direct solar radiation; and fined as cold if there were reports of frozen lakes or rivers, severe cold, heavy snow, or crop or tree dam- (2) the continuous rain is often caused by the invasion of cold air masses. Since it is possible to con- age due to cold weather. A year was warm if there struct the rainy day series from the Clear and Rain were reports of warm winters, no snow in winter, or Records, the temperature series can be retrieved by peach and plum blossoms in winter. In this way a using the above two factors. Zhang and Liu (1987) decadal winter temperature index ti was defined ac- first established a set of regression relations between cording to the decadal frequency of cold years (n1) the rainy day number and the monthly mean tem- and warm years (n2): ti=-[n1+0.3(10-n1+n2)]. perature using modern data sets. Then, assuming The results are shown in Fig. 11. It is seen that the that these relations are also valid for earlier times, 18th century was relatively warm compared to the they regressed the monthly mean temperature se- 16th and 19th centuries, the latter being the coldest ries of June and July of 1724-1903 from the rainy period. While some regional differences existed, it day number series of the Clear and Rain Records. appears that the variations of winter temperature

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Fig. 11. The curves of winter temperature indices in regions I-V and their 50-year running mean curves (solid lines), and the 10-year running mean values in regions VI-VIII. Dashed curve is from Zhu (1973).

The results are shown in Fig. 12. Since instrumental measurements of temperature were available for Beijing from 1891 and on (see Wang and Zhang, 1988), Zhang and Liu compared their reconstruction with the measured series as shown in Fig. 13. It is seen that the two have similar trends. Thus the reconstructed temperature series should reflect the actual variation relatively well. It appears that this method may also be applicable to other locations if similar data are available and the correlation between temperature and precipitation is good. Note that Fig. 12 shows the summer temperature so it is inappropriate to compare them with those winter temperature series mentioned above. 4. Reconstruction of humidity series using Fig. 12. Reconstructed monthly mean tem- historical documents perature series (A) and monthly mean maximum temperature series (B) of Bei- Monsoon activity manifests itself prominently in the precipitation. It is well known that the mon- jing in July (Zhang and Liu, 1986). soon rainfall is crucial to the crop yield in India (e. g., Lamb, 1972). This is true also to East Asia Lion records in Chinese historical documents because (Zhu, 1973; Yoshino, 1976). As mentioned previ- of its central importance to agriculture. ously, there exists a very large amount of precipita- Since the majority of precipitation in China oc-

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summer and fall. The remaining were occurring in other seasons. While results of these studies can provide information about the distribution of drought, they are not necessary equal to the annual humidity condition for one could have drought in one season and flood in another season during the same year. It is then difficult to determine whether this was a dry or wet year. In another earlier study (Nanjing University, 1977), the ratios of the flood frequency to drought frequency in a certain period were analyzed for the 17 provinces in the eastern half of China3. Fig- ure 14 shows the fluctuation of these ratios during a 50-year interval. It was suggested that the fluctuations of the two provinces in northern China Fig. 13. Comparison between measured and (Hebei and Shandong) were similar; that of the reconstructed annual temperature series of three provinces the middle reaches of the Yangtze Beijing, (Zhang and Liu, 1986). River (Hubei, Hunan, Jiangxi) were similar; and the two provinces in the south (Fujian and Zhejiang) curs in summer (see, for example, Tao, 1986; Sheng, were similar, albeit some differences in small fluctu- 1986), it is not surprising that most of the historical ations. The authors suggested that this shows that records about precipitation, such as flood, were also there were no dramatic changes in the monsoonal concentrated in summer. However, there were also circulations in the last 500 years. They also ob- records of continuous rain in spring and fall which served that the difference between Guangdong and often resulted in damage to crops but not necessar- Guangxi, which are roughly at the same latitudes, ily causing floods. Thus in historical records, both exceeded that between Fujiang and Guangdong. It damages from flood and continuous rain were re- was suggested that this would indicate that the pre- ported. Drought can occur in any season, but mostly cipitation of Guangdong is primarily due to the SE in summer, spring and fall. monsoon while that of Guangxi is partially due to The most extensive effort to reconstruct the hu- the SW monsoon. Combining the statistics of sev- midity conditions in the historical time in China eral provinces to represent the variation of larger ar- was carried out in the middle 1970s and early 1980s eas, the results are shown in Fig. 15. It shows that by a special task force involving hundreds of me- the phase of humidity variation in northern China teorologists, climatologists, geographers, historians, (e. g., Hebei and Shandong) was opposite to that of and other scholars. The final product is the book southern China (Fujian, Zhejiang, Hubei, Hunan, Yearly Charts as mentioned previously. The data and Jiangxi), especially in the 18th and 19th cen- sources were mainly local records, although a mul- turies. This pattern of "wet in the south, dry in titude of other types of documents were also uti- the north" or vice versa seems to persist even today. lized. The main kinds of records of concern were But it did not seem to exist in the 16th and 17th floods, droughts, and rains. Each entry was assigned centuries. This suggests that the monsoon circula- a grade from 1 to 5 based on the severity of the sit- tion at that time might be different from the recent uation, 5 being very dry, 4 dry, 3 normal, 2 wet, and 300 years. 1 very wet. A total of 120 stations were selected Zhang (1981) used the Yearly Charts data set to and their wetness/dryness grades of each year were study the variation of drought in China. A dryness determined. Then a wetness/dryness map was plot- index, ID=2D/N, is defined where D is the number ted for each year from 1471 to 1979. There are some of stations with wetness/dryness grade 4 or 5, and missing data in earlier years since not all 120 stations N is the total number of stations considered, so it possess adequate records. In addition to the maps, is actually the percentage of stations suffering from the original data used for plotting the maps are also the drought. Figure 16 shows the 10-year moving appended at the end of the book. Many analyses of average series of ID using the data of 100 stations in the humidity situation of China were based on this the eastern half of China. It is seen that the climate set of data. in the 16th and 17th centuries were relatively dry Earlier, Xiao et al. (1964) studied the drought 3 These provinces are Hebei , Shandong, Jiangsu, Anhui, conditions of the Henan province in the historical Hubei, Hunan, Jiangxi, Zhejiang, Fujian, Taiwan, Guang- time, taking their data mostly from local records. dong, Guangxi, Yunan, Guizhou, Sichuan, Henan, and They pointed out that in the period of 1630-1900, Shanxi. The data for the 15 were compiled by Xu Jinzhi 36% of the droughts occurred in summer, 26% in while the last two were compiled by Xiao Tingkui and Nie Shuren. both spring and summer, 18% in spring, and 13% in

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Fig. 15. Same as Fig. 15 except for combined areas. Curve-L is for Shanxi in this figure (Nanjing University, 1977).

while the 18th and 19th centuries were relatively wet. The 20th century appears to be a relatively dry century. Xu and Wang (1981) analyzed the wetness/ dryness grade series of the Yearly Charts data set. They pointed out that the frequency of severe drought increased with latitude. Thus northern Fig. 14. The ratios of number of flood-affected China (30° ～40°N) was the place with most frequent counties to the number of drought-affected and continuous severe drought. In fact, the dryness counties in each century for various index series of this region is highly correlated with provinces. the series for the whole country with a coefficient of 0.75 at better than 1% level. On the other hand, there was no obvious rule for high wetness, only that its frequency correlated well with severe drought, that is, very wet conditions usually occurred in the same periods of severe drought. Spectral analysis

Fig. 16. Dryness index series (10-year moving average) of eastern-half of China from 1470 to 1977 (Zhang, 1981).

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both the 10.4 and the 270 year periodicities may be associated with the solar activities. Xu and Wang also studied the relation between the humidity conditions and sea surface pressure. They calculated the correlation fields of the dryness index series of various latitudinal belts and found that the highest correlation regions, with negative coefficients, are located in the middle latitudes of the South Pacific, as shown in Fig. 17, the highest correlation being better than 0.1% level. This indicates that the winter subtropical high of South- ern Hemisphere has strong influence on the summer monsoon and precipitation of China. Xu and Wang explained this by the fact that a strong South Pa- cific High would push the ITCZ further to the north, a condition favorable to the formation of typhoons that would bring precipitation to the southern part of China. Figure 17 also shows that the highest correlation center moves further to the east as the drought belt of China moves further to the north. The reason of this relation is not yet clear. Patterns of the spatial distribution of humidity has been studied by Wang and Zhao (1981) and Xu and Zhang (1983). Wang and Zhao (1981) performed empirical orthogonal function (EOF) analysis on the Yearly Charts data set for 25 stations. The first three eigenvectors show mainly zonal distributions of humidity conditions (Fig. 18) while the higher-order eigenvectors give mainly meridional distributions. The significance of the zonal patterns is, of course, to be expected from the generally east- west orientations of climatic zones of China. Wang and Zhao (1981) suggested that the first eigenvector may be related to low frequency variations in the Southern Oscillation Index (SOI) which are linked with the western Pacific subtropical high. The second eigenvector also appears to be related to the position of subtropical high, specifically whether it extended north of the Yangtze River or not. The third eigenvector may be related to high frequency variations in the East Asian Circulation Index. The higher-order eigenvectors, although less dominant, nevertheless accounted for non-negligible vari- ance. Wang and Zhao suggested that the fourth eigenvector, which shows a reversal feature between the east and west of North China, may be associated Fig. 17. Correlation fields between drought with the presence or absence of high pressure over indices and July sea surface pressure. The the Sea of Japan. The fifth eigenvector, showing op- inner-most curve represents 0.001, the posite extremes in the eastern and western parts of middle curve 0.01, and the outer-most South China, may be associated with the frequency curve 0.05 significant level. (A) Region-1 of the occurrence of tropical cyclones over the south- (B) Region-2, and (C) Region-3, (Xu and east coast of China. Thus all these eigenvectors seem Wang, 1981). to have physically realistic interpretations. Based on these analyses, they divided the spatial patterns of showed that both the time series of dryness index historical humidity distribution into 6 types. and the wetness/dryness grade possessed periodici- Xu and Zhang (1983) extended the work of Wang ties of 2.4, 5.1, 10.4, and 270 years at more than 95 and Zhao (1981) by performing EOF analysis on the % confidence level. Xu and Wang conjectured that yearly charts data set for 100 stations. The first

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frequencies of Type-1 and 6 were about the same in the 16th and 17th centuries while in the 18th and 19th centuries Type-1 was more frequent than Type- 6 and Types-1, 2 and 3 were more frequent than Types 4, 5, and 6. In the present century Type-4 to 6 are most frequent. This is consistent with the findings of Zhang (1981). Chen (1989) studied the humidity conditions of Lake Taihu (in the Lower Yangtze region) in the period from 1121 to 1983 AD. Historical records of this region is especially abundant. There were only 21 years of missing records in the 863 years, thus rep- resenting a high quality data source. Most of the records were extracted from official histories, hy- drological records, and local records. The annual precipitation of this region is mainly due to Meiyu which is itself an indicator of the monsoon circulation. Figure 20 shows the results of this study where two main wet periods each spanning 200 years, were identified by Chen: 1300-1500 AD, and 1650-1850 AD. There were, of course, smaller fluctuations in these two periods. The Clear and Rain Records mentioned before have been utilized for the reconstruction of precipitation. The earliest work was that done by the Cen- tral MeteorologicalBureau of China (Central Me- teorological Bureau, 1975) for the reconstruction of monthly precipitation series of Beijing. The Clear and Rain Records of Beijing covers the period of 1724-1904. The retrieval of precipitation from it is facilitated by the existence of instrumental precipitation data for Beijing form 1841 and on. Thus, there was a period (1841-1904) when both instrumental observation and traditional observation used in the Clear and Rain Records existed. The instrumental data therefore can be used to calibrate the qualitative descriptions in the Clear and Rain Records. Figure 21 shows the reconstructed annual precipitation of Beijing from 1724 to 1904. It is clear that the late 18th and 19th centuries were wet periods of Beijing while the decades around 1750 and 1850 were relatively dry periods. More recently, Zhang and Wang (1989) and Wang Fig. 18. The first three eigevectors of drought and Zhang (1991) have carried out a detailed study and flood indices from 1470 to 1977 (Wang of the summer precipitation in the Lower Yangtze and Zhao, 1981). region using the Clear and Rain Records of Nan- jin, Suzhou, and Hangzhou. In order to convert the qualitative descriptions in the Clear and Rain three eigenvectors look very similar to that of Wang Records into quantitative precipitation series, they and Zhao (1981), thus confirming the above results. studied first the relations between the monthly pre- They also divided the flood-drought spatial patterns cipitation with the total frequency of monthly rainy into 6 types as shown in Fig. 19. Statistically, Type- days and the frequencies of various rain intensities 3 (wet in the south and dry in the north) occurred in these three cities using modern data and estab- most frequently in the last 500 years, averaging once lished a set of regression relations between them. every 4 years. Type-6 (dry in the whole country) was Applying these set of relations to the Clear and Rain rarest at once every 10 years. Type-1 (wet in the Records, they obtained the monthly precipitation whole country) occurred once every 7 years, while series of these three stations in the 18th century for Types-2, 4, and 5 occurred once every 6 years. The the months of May-August. These are shown in Fig.

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Fig. 19. Patterns of flood and drought distributions in China (Xu and Zhang, 1983).

22. These figures should reflect best the Meiyu (and sets. hence the summer monsoon) of China in the 18th Since the Meiyu is caused by the summer mon- century. Since the Clear and Rain Records are rela- soon front, its variation should reflect the monsoonal tively high quality historical data, the series, derived variation. Zhang and Wang (1991) studied the pre- from them can be used to check against other data cipitation series derived above to examine the char-

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Fig. 20. Humidity conditions of Taihu area from 1121-1983 AD. The curve represents the 30-year moving average of the dryness grades. Note the greater grades represent drier conditions. A grade of 5.0 is considered normal (Chen, 1989).

inactive cold air masses in the 40s-70s. The May frontal zones in the East Asian westerlies tended to be situated further to the north and the climate was warmer in general than other periods. Based on the modern observations in the relations between the subtropical high and Meiyu, Zhang and Wang (1991) also pointed out a sketch of the behavior of the western North Pacific High in the 18th century. 5. A sketch of the history of monsoon climate as revealed by the historical documents of China The reconstruction of past temperature and humidity series in China using Chinese historical literature has been reviewed above. Obviously there are Fig. 21. Reconstructed annual precipitation still many gaps of knowledge to be filled. However, series of Beijing based on the Clear and from the materials available at present time, we can Rain Records. (Central Meteorological at least sketch a general picture of the evolution of Bureau, 1975). the monsoon climate in China. This effort is further facilitated by the fact that not only one but several climate series are available, that is, we not only acteristics of summer monsoon circulation in East have temperature or humidity series, but also others Asia in the 18th century. Figure 23 shows the Meiyu such as winter thunderstorm and dust fall series. It seasons in the 18th century as determined by Zhang is often difficult to pinpoint the actual climate pro- and Wang (1991). Their study further shows that: cess if only one series is available. For example, it (1) There existed 2-3 and 5-6 quasi-periodicities is difficult to say from the precipitation series alone of Meiyu rainfall in the 18th century. The empty which circulational change was really responsible for Meiyu phenomenon (very low Meiyu rainfall) oc- a particularly wet period. But with the help of other curred once every 5-6 years. (2) Early Meiyu was series, the cause of the wet period can be made more more frequent in the 40s-70s, with 60s the climax certain. period in the 18th century. This seems to indicate

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Fig. 22. Reconstructed monthly precipitation series of May-August in (a) Nanjing, (b) Suzhou, and (C) Hangzhou based on Clear and Rain Records (Wang and Zhang, 1991).

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Fig. 22. (Continued)

5.1 Circulation types in warm and cold periods It is natural to expect that circulation types would change from a warm period to a cold period, and vice versa. In order to identify the differences in circulation types in different periods, we need to have some circulation indicators. In the present study, we can use the winter thunderstorm phenomenon as such an indicator. In explaining the negative correlation between the winter thunderstorm frequency and air temperature, Wang (1980) suggested that winter thunderstorms in China occur more often in colder climates because they are caused by the stronger frontal instability from the increased baroclinity. This requires that the meridional temperature gradients over the frontal zone would be greater in cold periods. The greater temperature gradient must have been caused by either a lower overall temperature of the cold air mass from the north or the more frequent invasion of cold polar air masses so that the above negative correlation can be explained. In other words, the colder winters must have been due to stronger cold Fig. 23. Meiyu seasons in Lower Yangtze air activities. reaches in the 18th century (Zhang and It is known from the studies of modern weather Wang, 1991). that stronger cold air mass activity corresponds to a lower index, or more meridional, circulation. This more north-south oriented circulation is favorable

310 February 1992 P. K. Wang 441

for cold air masses to move into China, causing se- the summer monsoon circulation is dominated by vere winters. On the other hand, a more zonal cir- the activity of North Pacific High. As mentioned culation would be unfavorable for cold air invasions. before, this is mainly reflected in the Meiyu phe- Thus it can be reasoned that during the colder pe- nomenon. From the study of modern Meiyu, the riods, the time-averaged circulations would be more following circulation types are found to be associ- meridional than in warmer periods. ated with certain Meiyu anomalies: (see Sheng et The more extreme form of the cold air activity al., 1986) is the cold outbreak phenomenon. Thus, by study- ing the conditions for cold outbreaks to occur in the (a) Early and High Meiyu-Meiyu started earlier modern time, we can gain some insights of the cir- than normal, usually in late May as opposed to culation patterns in the historical time. According the middle of June in normal years. In their re- to Sheng et al. (1986), there are three main routes cent study, Zhang and Wang (1991) found that via which cold outbreaks enter China: early Meiyu is well correlated with high Meiyu rainfall. For this situation to occur, the North (a) Northwestern route (NW)-Cold air enters Pacific High would move to the north earlier from the Ordos bend of Yellow River, passes than usually whereas the circulations in middle through Central China, and moves out from and high latitudes and in the upper levels above Middle and Lower Yangtze Basins. Occasion- Indian subcontinent would still remain similar ally the cold air can enter South China as well. to the spring pattern. The overall intensity of The typical weather caused by this type of cold the North Pacific High is rather weak. The 500 outbreak is characterized by high winds, rapid mb ridge of this High is more to the north. cooling, and dustfall. It also causes wide spread rainy and snow weather to the south of Yangtze (b) Low or Empty Meiyu-In low Meiyu years, the River. middle and high latitudes show little persistent meridional circulations. Westerlies in the lower (b) Eastern route (E)-Cold air enters from the latitudes are weak. The overall intensity of the northern part of North China or the southern North Pacific High is strong, its center position plains of Northeast China (Manchuria). The more to the east and south. main body of the cold air then moves to the Sea of Japan while the remaining parts move The summer circulation is somewhat more com- through North China and Lower Yellow River plicated than the winter, and its relation with Meiyu reaches and enter Hunan and Hubei Basins. needs to be further clarified. But the general behav- This type of outbreak often causes high NE ior of the Northern Pacific High as described above winds in the areas of Bohai Gulf, Yellow Sea, appears to be reasonable and can be used to describe and Lower Yellow River Reaches. It also caused the circulations associated with Meiyu. Due to the snowy and cold weather in the region north of lack of a detailed understanding of the summer mon- Yangtze River. soon situation at present, the following discussion will focus on the winter conditions. (c) Western route (W)-Cold air enters from Xin- jiang Province, passes through Gansu and east- 5.2 Monsoon climates and circulations in the histor- ern Sichuan Provinces, and then moves south- ical time of China eastward. The intensity of this type is the low- Using the knowledge described in the above sec- est of the three and influences mainly north- tions, we can now sketch the general climate condi- western, southwestern, and southern China. tions and the associated circulations in the historical The magnitudes of cooling are usually smaller time. than the other two types. Figure 24 shows the superimposition of the win- Zhang (1991) studied the relation between the ter temperature fluctuations of China by Zhu (1973), cold air outbreaks and the winter temperatures in the winter thunderstorm series, and the dust fall se- Shandong, Jiangsu, and Guangdong Provinces in ries for the period of 300-1900 AD. The latter two the last 500 years and found that the NW and W series are expressed in terms of the 50-year running types of cold outbreaks dominated in cold periods mean of the decadal frequency. All three series rep- whereas dominated in warm periods. The NW and resent the overall conditions of China and appear to W types also correspond to the situation where the be fairly consistent with each other. Note that the Main East Asian Trough is located more to the west temperature curve is presented in an "upside down" and deeper, as revealed from the studies of modern manner so that the higher on the curve means colder data. This should be also the dominant circulation temperature. From this figure, we can make the fol- in colder periods. lowing sketch of the general climatic change of China In contrast to the above winter monsoon circu- in the past 1600 years: lation which is dominated by the cold air activity,

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Fig. 24. Superimposition of winter thunderstorm frequency (Wang, 1980) dustfall frequency (Zhang, 1984), and winter temperature (Zhu, 1973). The frequency curves represent the 50-year moving average of decadal frequencies.

(1) 300-500 AD-This was a period of relatively (3) 800-1100 AD-This appears to be another rel- cold climate, corresponding the the relatively atively warm period but had the tendency of turmoil period of West and East Jin and North becoming colder at the end of this period. Win- and South Dynasties of China. It was also a pe- ter thunderstorms, which were dormant in the riod of more frequent winter thunderstorms, al- previous period, became more frequent. Dust- though the dust fall frequency was only slightly fall also picked up its activities. This period higher than the subsequent period. It is not extended from the late Tang Dynasty to early known whether this latter discrepancy is due to Song Dynasty (960-1279). In between these the inadequacy of data or a special circulational two dynasties was the so-called "Five Dynas- condition. From our reasoning above, the gen- ties and Ten States" period, a relatively unsta- eral circulation would be more meridional over ble time politically. Plum trees became extinct China in the winter time. in North China. Lake Taihu was frozen for the first time in history in 1111 AD. The lake ice (2) 500-800 AD-The climate became warmer. was thick enough to allow vehicle traffic. Cit- There was a minimum of dustfall frequency in rus trees in Taihu area were destroyed. Clearly 550-650 AD which might indicate a relatively more meridional mean circulations prevailed in humid period. Winter thunderstorm frequency this period. dropped to zero at this time. These indicate that circulations were more zonal and the cold (4) 100-1400 AD-Climate quickly turned to very air activities were weak. cold, as seen in the temperature curve. Both Politically, the year 581 marked the end of the winter thunderstorms and dustfall occurred very frequently in this period. This means that fragmentary state of China and the establish- cold outbreaks occurred frequently and severe, ment of a unified Sui Empire. Although Sui causing great suffering of people. It was also a last only 37 years (581-618), the Tang Dynasty relatively dry period, as indicated not only by (618-907) that followed it enjoyed a relative sta- bility and was considered as one of the golden the high dustfall frequency but also the wet- ages of Chinese culture. Trade activities on the ness/dryness grade of Taihu area in Fig. 20. Silk Road reached its peak (may be also climate The Song Empire had been greatly weakened related?). The favorable climate in China at when Emperor Huizong assumed the throne in 1100 AD. The Northern Song Dynasty soon this time was characterized by the warm winters as the frequent reports of "no snow in winter" ended and the Southern Song Dynasty started in the History of Tang Dynasty could attest. in 1131 AD. It was replaced by the Yuan (Mon- Citrus trees could be grown and bear fruits in golian) Dynasty (1280-1368 AD). The Yuan Xian-an impossibility in present climate. navy invaded Japan twice but met with ty-

312 February 1992 P. K. Wang 443

Fig. 25. Superimposition of (1) winter temperature series of Hunan and Jiangxi Provinces (Zhang, 1980), (2) decadal frequency series of cold winters (Zhang and Gong, 1979), and (3) Dryness index series (Zhang, 1981).

phoons in both occasions. This might say some- briefly sketch the general situations. thing about the summer monsoon circulation at this time. Figure 25 shows the superimposition of several series indicating the temperature and humidity conditions. (5) 1400-1500 AD-This appears to be a brief In the following, we shall combine Fig. 24 and 25 for warm period. Both winter thunderstorms and discussions. dustfall were rare. Figure 20 indicates a wet climate in the Lower Yangtze region at this time. (a) 1470-1520 AD-This period was marked by high frequencies of both winter thunderstorms This was the early part of Ming Dynasty (1368- and dustfall and cold winter temperature. The 1644 AD) during which China enjoyed some trend was also very clear in Fig. 25 which also prosperity. The famous ocean expeditions by Admiral Zheng He occurred in the years be- indicates an unmistakably dry climate. There 6 tween 1405 and 1433. The rarity of winter thun- years during which lakes and rivers in Yangtze and Huai River regions were frozen. Unusually derstorms indicated a more zonal winter mon- severe cold outbreaks and heavy snowfalls oc- soon circulation. curred in 1493 in the east coast. Snowfall con- Later in this period, the climate turned colder. tinued off and on for 5 months. The sea water A major severe drought occurred in 1470, caus- near the northern coast of Jiangsu was frozen. ing widespread famine in Northern and Cen- Figure 20 shows a dry climate at this time in tral China. As we have seen, drier conditions Taihu area. tend to be associated with colder climates in (b) 1520-1620 AD-Another brief mild period. general in the long term sense (>30 years). The dip in winter thunderstorm and dustfall Thus droughts tend to occur more frequently frequencies were obvious. in colder periods. Although the rebellion by the famine refugees was suppressed this time, (c) 1620-1720 AD-The climate became cold and more were to come in the following period. dry again. Both winter thunderstorms and dustfall frequencies reached all time high. (6) 1500-1900 AD-The period between 1400-1900 There were 10 years where the freezing of was the so-called little ice age. This also hap- lakes and rivers in Yangtze and Huai River pened to be the time when Chinese scholars regions were reported. Citrus plantations in compiled thousands of volumes of local records Jiangxi Province, established since Tang Dy- which provide a rich source for the climate re- nasty, were completely destroyed in the two se- construction, as mentioned before. Detailed de- vere winters of 1654 and 1676. The climate in scriptions of the wet and dry conditions can be this period also showed great variability. Ex- seen in the Yearly Charts. Here we shall only tremes occurred frequently. For instance, in

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of Chinese historical documents. The reconstructed climates show clear fluctuation. Cold periods were usually associated with dry climates and vice versa. Unusual weather phenomena such as thunderstorms in winter and dustfall tended to occur more often in colder climates. Extreme weather also tended to occur more frequently in colder periods. All these indicate that colder climates are usually associated with greater variabilities. Although the details are still pending, it can be said that the circulations of winter monsoon in China would be more meridionally oriented in colder periods judging from the negative correlation between the temperature and winter thunderstorm frequency. Thus the northerly components of the winter monsoon must have been particularly strong in these periods. It would be desirable to have other evidence to support this conclusion. The summer monsoon conditions would be revealed by the more detailed studies of the Meiyu fluctuations. This Fig. 26. Comparison of the climatic changes work is still on-going. between China, Europe, and Japan. "C" represents cold and "W" represents Finally, when the more detailed studies be- come available, it will be possible to compare the warm. (Zhang, 1991). global climatic change and the associated circulation changes. Recently, Zhang (1991) compared the cli- 1609, both Jiangxi and Fujan Provinces suffered matic changes between China, Europe, and Japan, from heavy flood with death toll in hundred of and the results are shown in Fig. 26. It is obvious thousands in both places. In the same year that the fluctuations in these three places were more severe locust disasters occurred in Shandong or less synchronous, although some shifts in phase Province and severe drought occurred in Shanxi existed. Whether the climatic change in Europe oc- Province. Famine refugees rebelled in 1628 af- curred earlier than in China or vice versa is still be- ter another severe drought occurred in North- ing debated. With more information in the future, ern China. This rebellion, led by Li Zicheng, it is hopeful that these issues can be resolved. finally toppled the Ming Dynasty. Heavy snow were reported in 1653 (as thick as 3 meters on Acknowledgements the ground) and 1670 (snow continued for 20 days, coastal sea ice piled up and extended for This work is partially supported by U. S. NSF several kilometers offshore). Grants ATM-9002299, ATM-8511905, and Univer- sity of Wisconsin Graduate Research Fund 135-3169 (d) 1720-1830 AD-This was another warm pe- and 135-3341. riod. Again both thunderstorms in winter and dustfall were rarer in this period, as seen by the References gap in Fig. 24. This kind of consistency makes the results and interpretation more credible. Academy of Metorological Science. 1983: Yearly Charts of Dryness/Wetness in China for the Last 500 Year (e) 1830-1890 AD-a cold period. There 9 years Period. Photograph Publishing House, Beijing, with reports of frozen lakes and rivers. In 1845, 332 pp (in Chinese). both Yellow and Huai Rivers were frozen for Bryson, R.A. and T. J. Murray, 1977: Climates of about 40 days and river ice was thick enough Hunger. Univ. of Wisconsin Press, Madison, 171 pp. to allow vehicle traffic. Heavy snow and ex- Bryson, R.A., 1989: Late quaternary volcanic modula- tremely cold weather were also reported in the tion of Milankovitch climate forcing. Theor. Appl. same year. Climatol., 39, 115-125. Central Meteorological Bureau, 1975: Annual Precipi- All the above descriptions can be seen in Zhu tation of Beijing. Central Meteor. Bureau, Beijing, 46 pp (in Chinese). (1973). Chen, Jiaqi, 1989: A preliminary research on the regu- 6. Conclusions larity and factors of changes of flood and drought in Taihu Lake Basin since the Southern Song Dynasty. It is seen above the past monsoon conditions in Acta Geogr Sinica, 9, 25-33 (in Chinese). China can be reconstructed using the rich sources

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過去の東アジアモンスーン気候を中国の歴史文献より再構築する最近の研究

P.K.Wang (ウィスコンシン大学気象学教室) D.Zhang (国家気象局気象科学研究院)

中国の歴史文献に基づく、東アジアモンスーンの影響を受けた中国の地域の気候を再構築する研究をレビューする。歴史文献より求められる一般的な気候情報を議論し、いくつかの具体例を示す。より定量的な再構築のために有用な文献を挙げ、その評価を行う。しかる後に冬と夏の気温及び乾燥/湿潤のシリーズの再構築をレビューし、議論する。気温の再構築は主として湖や川の凍結、鳥の渡り、降雪の開始や終了といった生物気候学的な記録の気候的解釈に基づいている。中国の様々な地域における気温のシリーズの再構築例を示す。ついで湿度のシリーズの再構築をレビューする。この目的のための資料源は主として洪水、干ばつ、及び降雨の記録である。毎日の気象報告や清朝晴雨録のような高品質の資料源についても議論する。これらの再構築をもとに紀元300年から1900年の期間における中国のモンスーン気候の一般的な動向をまとめ、短い結論を述べる。

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