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TEMPERATURE AND PRECIPITATION INTERDECADAL VARIABILITY IN CHINA SINCE 1880

WANG Shaowu and ZHU Jinhong

Department of Atmospheric Sciences, School of Physics, Peking University, Beijing 100871, China

ABSTRACT

Reconstruction of homogeneous seasonal temperature and precipitation series of China is crucial for proper understanding climate change over China. The annual mean temperature anomaly series of ten regions are founded from 1880 to 1990. Positive anomalies over China during 1920s and 1940s are noticeable. Linear trend for the period of 1880-1999 is 0.62°C/100a, a little greater than that of the globe (0.60°C/100a). 1998 was the warmest year in China since 1880, it is in agreement with estimation of the global mean temperature.

The mean precipitation in national scale depends mainly on that over the East China. Variations of precipitation in some areas of the West China show negative correlation to the national mean. It is evident that the 1920s was the driest decade for the last 120-years. The most severe drought of national scale occurred in AD 1928. Severe droughts also occurred in 1920, 1922, 1926 and 1929 in the North China. It is noticeable that precipitation over the East China was generally above normal in the 1950s and 1990s and severe floods along the Changjiang River in 1954, 1991 and 1998 just occurred in these two wet decades. Increasing trend in precipitation variations observed in West China was not found in East China, where 20 to 40-year periodicities are predominated.

 

I. INTRODUCTION

Examination of climate change depends fully on the availability of a homogeneous and consistent data set. Systematical observations on national scale in China began at 1951. This data set consists of monthly mean temperature and monthly total precipitation observations at 160 stations, which cover nearly the whole land area of the nation except Taiwan. However, observational data are still scarce in some local areas, for example, over the southwest of Tibet.

Analyses of temperature changes since 1951 indicated that temperature decreased from 1950s to early 1970s, and then increased gradually, the highest warming was found during the later part of the series in winter over north part of the country (Hulme et al. 1992,1994, Ding et al. 1995). Temporal change of annual precipitations differed greatly from that of temperatures. Usually, a decline trend was found from 1950s to 1980s in annual total precipitation changes (Li et al. 1990, Wang B M 1996). Interdecadal variability plays a prominent role in this time interval, positive anomalies predominated from early 1950s to middle 1960s, from early to middle 1970s and in early 1980s.

50-year length of the data set seems not enough for understanding the long-term trend and interdecadal variability of temperature and precipitation. Many efforts had been made to extend the climate series back to the beginning of the 20th century or the end of the 19th century (Yang 1956, Yang 1962, Zhang and Li, 1982, Weather and Climate Institute, 1984). A grade series of monthly mean temperature and total precipitation was carried out in Weather and Climate Institute, China Meteorological Administration. Therefore, monthly mean temperatures for a calendar month and for each station have been grouped into five grades according to the absolute values of temperature. This method is exactly as same as which was used by Namias (1953) in studying long range forecast in the U S. It avoids of finding a consistent normal time to calculate departure from the normal. Grading of observational data is nearly free of impact of gaps in the series. The missing data of grade are easy to interpolate according to the grades in neighbor stations.

Zhang et al. (1982) firstly indicated on the basis of temperature grade data that temperature changes over China nearly parallel to that over the globe. Considering the limitation of grade series of temperature, Wang (1990) constructed an annual mean temperature series of China, which was combined stational data (1880-1910) and grade data (1911-1988) that had been transformed into temperature anomalies. Lin X C et al. (1990,1995) also extended the temperature series back to 1873 using observational data. But the number of stations used in the study varied significantly from only 5 at the end of 19th century to 330 in 1950.

The first series of precipitation over China longer than 50 years was established by Zhang M L (1993). Chen and Ding (1996) updated temperature and precipitation grade data set to 1990 and indicated that precipitations were relatively plentiful in the 1910s, 1930s and 1950s. The driest decade occurred in 1920s, but did not appear in the second half of the 20th century. Those researches improved understanding on the trend and variability of precipitation.

The reconstruction of new temperature series over China is described in section two. And the construction of seasonal precipitation series of the East China and decadal variability of annual precipitation in West China will be presented in subsequent sections.

 

II. RECONSTRUCTION OF NEW TEMPERATURE SERIES OVER CHINA

Both identical number and similar coverage of stations are essential to construct a homogeneous national series of temperature. Variance of national mean temperature depends on the number of stations used in construction. Great portion of land area of the country left blank in meteorological observations during the late 19th and the early 20th century. It influences significantly the representative of the mean value for the nation.

Therefore, the first step in construction of national mean temperature series is to divide the land area of the country into some regions. The key stations for each region and the name of each region are listed and each of central stations is marked with star (Table 1). Geographical locations of the stations are shown in Fig.1.

 

 

Fig.1. Ten climatic regions named by number and position of 160 stations over China, the key stations and central stations are marked by dots and stars, respectively.

 

Table1. Regionality of Temperature Changes of China

No.

Region

Stations

1

Northeast

Qiqihar, Jiamusi, Harbin*, Changchun, Shenyang

2

North

Beijing*, Taiyuan, Jinan, Zhengzhou, Xuzhou

3

East

Nanjing, Shanghai*, Hangzhou, Jiujiang, Wenzhou

4

South

Nanning, Guangzhou*, Shantou,Xiamen, Zhanjiang

5

Taiwan

Taipei*, Taizhong, Tainan, Penghu, Hengchun

6

Central

Wuhan*, Yichang, Changsha, Changde, Zhijiang

7

Southwest

Chengdu, Chongqing, Xichang, Guiyang, Kunming*

8

Northwest

Yanan, Xi¢ an, Lanzhou, Xining, Jiuquan*

9

Xinjiang

Altay, Urümqi, Hami, Kashi, Hetian*

10

Tibet

Lhasa*, Qamdo, Yushu, Maduo, Ganzi

Identification of key and central stations is made according to correlation coefficients (CCs) among the stations, considering the availability of observational data. Then, regional temperature series are constructed by averaging the observational data over the five key stations for each of the ten regions for the period of 1951-1999.

During the second period (1911-1950), temperature grade data are available (Weather and Climate Research Institute, 1984) for the seven regions except Xinjiang, Tibet and Taiwan. Temperature observations are available in Taiwan for this period. Temperature grades for the other seven regions are transformed into temperature anomalies according to the ratio of grade to temperature anomaly, which varies from month to month and from place to place. Studies indicate that temperature anomalies in Xinjiang are closely correlated to ice core d18O in Guliya (Wang et al. 1998). CCs vary from 0.25 to 0.35, which reaches significance at 95% of confidence level. Therefore, annual mean anomalies of d18O in Guliya from 1880 to 1950 are normalized relative to the normal period of 1961-1990, then multiplied by temperature variance of Xinjiang for the period of 1961-1990 to construct the temperature anomaly series represented temperature variations in Xinjiang before 1951. In Tibet, few temperature observations are available before 1951. The gaps in the observations are filled with tree-ring data. It is believed that the latter correlates closely to temperature anomalies in Tibet (Lin Z Y and Wu X D 1977).  

Since no grade data can be used during the first period (1880-1910), construction of temperature series has to rely upon single stational observations in the first five regions. Even though, only the series of Shanghai and Beijing are complete, the series of Harbin, Guangzhou and Taipei began some later than 1880. Wang (1990) filled the gaps in the series of Harbin and Guangzhou with observational data of Nemuro in Hokkaido, Japan and of Hong Kong, respectively. A few gaps of Taiwan¢s series are filled with documentary data. In both Central and Southwest regions, annual temperature grade is identified according to documentary data when observation is obscure (Wang et al. 1998). Firstly, temperature grade is estimated based on historical documentations, and then transformed into temperature anomalies using normal distribution of temperatures for the period of 1961-1990. Methodology of the transformation was described in detail by Wang et al. (1998). δ18O anomalies in Dunde were used to reconstruct temperature in the Northwest region as done for the Xinjiang.

 

 

Fig.2. Ten regional temporal variations of annual mean temperature anomalies from 1880 to 2000, from top to bottom, each one represents the annual mean temperature anomalies for each climatic region outlined in Table 1. The solid line is for filtering line considered Gauss weights.
Finally, the annual mean temperature anomaly series of ten regions are founded from 1880 to 1990. Figure 2 gives ten regional series of annual mean temperature anomalies from 1880 to 2000. Temperature anomalies are founded relative to the normal of 1961-1990. Figure 3a shows the temperature series of China, which is averaged over ten regions considering the regional weights. Global mean temperature anomaly series is also shown in Fig.3b for comparison. Positive anomalies over China during 1920s and 1940s are noticeable. Linear trend for the period of 18801999 is 0.62°C/100a, a little greater than that of the globe (0.60°C/100a). 1998 was the warmest year in China since 1880, it is in agreement with estimation of the global mean temperature (Wang et al., 2000; 2001). The warming trend found on the basis of new series is much greater than that estimated by using incomplete data (Wang 1990, Yi and Wang 1992).

 

 

Fig.3a. Temporal variations of annual mean temperature anomalies over the east part of China from 1880 to 2000, positive anomalies are shaded. The solid line is for filtering line considered Gauss weights.

 

Fig.3b. Temporal variations of annual global mean temperature anomalies from 1880 to 2000, positive anomalies are shaded. The solid line is for filtering line considered Gauss weights.

III. CONSTRUCTION OF SEASONAL PRECIPITATION SERIES OF THE EAST CHINA

It has been demonstrated that variability of precipitation over China depends mainly on that over the East China (east of 110° E) (Wang et al. 2000). Variations of precipitation in some areas of the West China even show negative correlation to the national mean. Therefore, precipitation variations should be studied separately for the east and west part of China.

There is also another strong reason to examine precipitation variability in the east independently to the West China. Proxy data sources of precipitation are quite different in these two parts of the country. Documentary data of precipitation are plentiful in the east, but is obscure in the west. Fortunately, a great deal of tree-ring data provides important information of precipitation variability in the west China.

 

Table 2.  Availability of Observational Precipitation Data

 

 

Station

 

Beginning

Missing data

 

 

Station

 

Beginning

Missing data

1880-1899

1900-1950

 

1880-1899

1900-1980

Harbin

1898

18

8

 

Xinyang

1922

20

41

Changchun

1909

20

13

 

Yichang

1882

2

12

Shenyang

1906

20

10

 

Wuhan

1880

1

9

Caoyang

1908

20

26

 

Changsha

1909

20

16

Hohhot

1920

20

21

 

Jian

1930

20

30

Beijing

1840

4

7

 

Guilin

1916

20

16

Taiyuan

1916

20

29

 

Nanning

1907

20

7

Jinan

1916

20

16

 

Guangzhou

1908

20

7

Zhengzhou

1931

20

41

 

Shantou

1880

0

7

Xuzhou

1915

20

28

 

Zhanjiang

1951

20

51

Yantai

1886

16

12

 

Yinchuan

1935

20

47

Nanijing

1905

20

6

 

Lanzhou

1932

20

32

Shanghai

1873

0

0

 

Xian

1922

20

25

Jiujiang

1885

5

12

 

Chengdu

1906

20

17

Wenzhou

1883

4

0

 

Chongqing

1891

11

0

Fuzhou

1880

7

0

 

Guiyang

1921

20

0

Taipei

1897

17

0

 

Kunming

1901

20

7

Hengchun

1897

17

0

 

total

 

542 77.4%  553  31.0%

 

Totally 35 stations are selected to form a homogeneous series according to the availability and quality of observations (Table 2). By the way, all of these 35 stations are located in the area with 0.2 or greater CCs to the national mean precipitation. Availability of precipitation observations is much better than that of temperatures. Totally 13 stational series with complete precipitation observations began at 19th century, while only 4 to 5 for the temperature observations. However, there are still 77.4% missing data for the period of 1880-1899, and 31.0% for the period of 1900-1950. These gaps in observations are filled based on documentary data. Reconstruction of drought/flood grade maps for the last 500 years (AD1470-1979) provided valuable information of precipitation variability in the east China. These maps referred mainly to the summer time. It is easy to transform the grade of drought/flood into the rainfall anomalies in percentage according to the definitions: grade 1-50%, grade 2: 25%, grade 3:0%, grade 4:-25%, grade 5:-50%. Usually, several items of records are used to estimate the precipitation grade in one season at a station, where stational observation is not available.

 

Only observations are applied for the period of 1951-1999. Figure 4 gives seasonal precipitation series averaged for 35 stations during the period of 1880-1999. The lower panel of Fig.4 shows annual precipitation variations. A decreasing trend in precipitation variations has been found based on the observations since 1951. However, it seems end in the 1980s. A weak increasing trend is observed in the 1990s. At the same time, no linear trend occurred during the first period from 1880 to 1950. 20-40 year-periodicity is predominated for the whole series. Power spectrum analysis (not shown) indicates a significant peak around 30-years, and a weaker peak near 3-years.

 

 

 

Fig.4.  Seasonal precipitation anomalies averaged for 35 stations during the period of 1880-1999 (mm), positive anomalies are shaded. The solid line is for filtering line considered Gauss weights.

IV.  DECADAL VARIABILITY OF ANNUAL PRECIPITATION IN WEST CHINA

In the most area of the West China, documentary data are scarce and constructions of precipitation series in early time rely mainly upon tree-ring data. The climate characteristics over there belong to arid or semi-arid type and annual precipitation is usually less than 200 or 400 mm except in southeast of the Tibetan Plateau and in the far west of Xinjiang. Changes of tree-ring width in West China reflect in great extent the precipitation variations. A lot of papers have contributed to reconstructing local precipitation series in the West China.

Only the decadal mean precipitation anomalies in percentage, which represented the low frequency variability of precipitations, show greater reliability than the high frequency part. For example, the width of tree-ring in each year depends usually not only on the climatic condition in this year, but also on that in last year or even in the year before last year. CCs between decadal mean widths and precipitations show higher confidence level than the yearly data. It needs to note that it is very difficult to estimate the absolute amount of precipitation, for all of the tree-ring data was taken in the border of the forest where usually no observatory occurred. In general, the CCs between width and precipitation vary from 0.4 to 0.5. Therefore, the part of the precipitation variance interpreted by the width only varies from 15% to 25%. The tree-ring data are normalized relative to the normal period of 1961-1990, and then multiplied by the variance of annual precipitation in the nearby station. This procedure avoids in some extent reduction of the variance of reconstructed series. Most of the series of proxy data ended in 1980s. Then they were updated with the help of observational data. Figure 5 gives the mean precipitation anomalies from 1900s to 1990s relative to the normal (1960s-1980s). It shows tremendous drought in 1920s-1930s and an increasing trend from 1930s to the end of the 20th century.

 

Fig.5. Decadal mean precipitation anomalies in percentage for the period of AD 1900s-1990s over the western China, positive anomalies are shaded.

V. CONCLUSION

The new temperature series over ten climatic regions of China and whole China were reconstruction. The homogeneity and coverage of these series were considerably improved. According to this series, linear trend of surface air temperature over China for 1880-1999 is 0.62°C/100a, a little greater than that of the globe, and its variability is much greater. Both seasonal precipitation series over the eastern part of China and decadal variations of annual precipitation in West China were reconstructed. It is quite different of precipitation variation for East and West China. There was no linear trend during 1880-1999 and 20-40a oscillation is predominated for the whole series of the eastern part of China. On the contrary, the increasing trend of precipitation in west China is very noticeable in the second half of 20th century.

Acknowledgments: This work was supported by National Key Basic Research Special Funds of China (G1998040900) and Natural Science Funds (40205011).

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