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·Climate Changes of the Past 100 Years in China

Climate Changes of the Past 100 Years in China

·Ren Guoyu Xu Mingzhi Tang Guoli Zhang Li Liu Hongbin Zhai Panmao,
Ren Fumin, Zou Xukai, Chu Ziying
(National Climate Center, China Meteorological Administration)

·Guo Jun
Climate Service Center, CMA, Tianjin Meteorological Bureau

·Liu Xiaoning Li Qingxiang Wang Ying
(National Meteorological Center, China Meteorological Administration)

·Chen Zhenghong, Yang Hongqing
(Hubei Institute of Meteorological Science and Technology, China Meteorological Administration)


A major unresolved issue in basic science of climate change is the detection of global and regional changes in climate and the attribution of the changes to specific factors, in particular the increased CO2 concentration in atmosphere (Houghton, et al., 2001). A study on this issue was initiated as a component of the National Key Project "Research on Global Environmental Changes and the Responding Policies" sponsored by the Ministry of Science and Technology of China. Its goals are: (1) to add or assess the time series of climate change of China on varied time scales with an emphasis of the past 50 years and 100 years, and to analyze the temporal and spatial characteristics of the changes; (2) to understand the historical changes of climate extremes in the country; and (3) to understand the possible causes of the regional climate changes of the past 100 years.

1. Data and methods

A data set of mean temperature, precipitation and other climate elements for 710 stations across Mainland of China were used. The data set has been processed carefully, and the main in-homogeneities existing in the mean monthly temperature data for the last 50 years have been checked and corrected. There were serious problems in the mean monthly temperature data prior to the pre-1950s and the biggest one is with the observation times within a day. In order to solve the problem, mean monthly temperature data obtained by averaging mean monthly maximum and minimum temperatures for the 100-year temperature series were used. The widely accepted procedures for creating area-averaged climatic time series and for calculating linear trend have been used (Jones and Hulme, 1996). Tendency of climatic variables for all stations was also calculated, which is defined as the correlation coefficient between values of a climatic variable and the numbers of its time series for each station.
Analyses have been made for annual and monthly temperature, precipitation, pan evaporation, sunshine duration, wind speed, and the frequency of major extreme climate events. Some interesting results have been obtained so far, which are summarized as follows:

2. The last 50-year temperature

Mean annual surface air temperature in Mainland of China rose by about 1.1 ℃ for the last 50 years as a whole, with a warming rate of about 0.22℃/10a. The warming in the later half 20th century is more rapid than the average values of the world and the Northern Hemisphere as given by Jones, et al. (2001) or IPCC reports (Houghton, et al., 2001). The most evident warming occurred in winter and spring as expected. Unexpectedly, however, nearly 60% of the warming occurred in the last 16 years, which account for only about 30% length of the period of 1951-2001. Large spatial difference exists in the changes of surface air temperature as well (Fig. 1). Northeast China, North China and Northwest China experienced more significant warming in terms of mean annual temperature, while a cooling trend reported in earlier studies is still continuing in southwestern China . Summer mean temperature in the middle and lower reaches of the Yangtze River also de creased in the last 50 years.

Fig. 1 Tendency of mean annual temperature in China from 1951 to 2001

As a result of warming, growing season as defined based on mean daily temperature increased 6.6 days in China as a whole over the past 40 years. More evident lengthening of growing season can be found in northern China, and the largest increase in growing season, 18.2 days for the period, occurred in the Qinghai-Tibetan Plateau. 1990s witnessed the most rapid increasing of growing season, and 1998 was a year with the longest growing season in the past 40 years.

3. The last 100-year temperature

Mean annual surface air temperature of the country for the past 100 years also experienced a significant warming, though the warming rate of 0.08℃/10a for the period analyzed is much lower compared to the last 50 years. Two warm periods, which occurred in 1937-1948 and 1987-2001, respectively, were evident, with 1946 and 1998 as the warmest ones within the record period. It is interesting to note that the temperature anomalies of 1990s were no higher than those of 1940s. Seasonal features of temperature changes for the last 100 years bore a very clear similarity with those for the last 50 years, with the most rapid warming occurring in winter and spring.

4. Problem with urbanization effect

The above-mentioned results were all based on a data set of surface air temperature without suffering any correction for urbanization bias. This might be a big problem with regard to the unprecedented urbanization processes for most of the meteorological stations. In Beijing region, for example, temperature records from two national basic/reference stations used in constructing temperature series of the past 50 years were significantly impacted by urban warming, especially for the last 20 years. Warming induced by urbanization or enhanced heat-island effect in the two stations accounts for about 70% of the total increase in mean annual temperature for period from 1961 to 2000. This case indicates the essentiality to pay more attention to the effect of urban heat island magnitude change on long-term mean temperature series in the country.

5. Changes in precipitation and other variables

Less confidence could be thrown to the precipitation data. In spite of the problems with data, it is still worth noting that no significant long-term change in the country-averaged annual precipitation was obtained for both the past 50 years and the past 100 years. However, an obvious tendency of drying in the Yellow River Basin and the North China Plain in terms of precipitation has been found for the later half of 20th century, and the largest drop in precipitation occurred in Shandong Province. Meanwhile, an insignificant wetting trend in the Yangtze River Basin and most parts of western China could be detectable. For the Yangtze River Basin, the increased annual precipitation mainly resulted from the significant rising of summer rainfall, though winter precipitation also tended to increase.

Fig. 2 Tendency of precipitation in China (1961-2002).
(Blue color: positive trend; Red color: negative trend)

Since 1956, the country-averaged pan evaporation has had a significant tendency to decrease, with a changing rate of -34.5mm/10a. The most significant decrease occurred in spring and summer in the North China Plain and the lower reaches of the Yangtze River. The largest decrease in Pan evaporation in terms of absolute values is in northwestern China. It is worth noting that average sunshine duration and wind speed were also experiencing a tremendous drop in most regions of the country during the past 50 years, and they usually bear a similarity with pan evaporation in spatial pattern of the tendencies. In parts of the North China Plain, annual sunshine duration in the recent years is almost 500 hours fewer than that of 50 years ago.

6. Extreme weather and climate events

A mixed picture could be seen for extreme weather and climate events for the past 50 years. As expected, country-averaged daily minimum temperature and days with minimum temperature below 0℃ have been decreasing since 1950. However, country-averaged daily maximum temperature and days with maximum temperature above 35℃ have not tended to significantly increase. Obvious increase in days with heavy rain in the Yangtze River Basin and in the area suffering serious drought in North China Plain and southern Northeast China has been found for the recent 50 years, while no significant change in the extreme precipitation events has been detected for the country as a whole. In addition, rainfall resulting from typhoon tended to decrease since 1954. Dust storm, a disastrous weather phenomenon in northern China, also experienced a significant decreasing trend in number of days over the last 50 years (Fig. 3).

Fig.3 Tendency of days with dust-storms in China(1960-2000).
(Blue color: positive trend; Yellow color: negative trend.)

Acknowledgments: This study was funded by the Ministry of Science and Technology of China (2001BA611B-01) and the Ministry of Water Resource of China.

(Guoyu Ren: E-mail: gyren@homeway.com.cn)

References

Houghton, J. T., Ding, Y. H., et al., eds., 2001: Climate Change 2001: The Scientific Basis. Cambridge University Press, Cambridge, 896 pp.
Jones, P. D., and M. Hulme, 1996: Calculating regional climatic time series for temperature and precipitation: methods and illustrations. International Journal of Climatology, 16: 361-377.
Jones, P. D., New, M., Parker, D.E., et al., 1999: Surface air temperature and its changes over the past 150 years. Reviews of Geophysics, 37 (2): 173-199.

Source: Climate Change Newsletter(2003/2004)

Date:Aug 02,2005