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The Current Climate Characteristics And Topographic Climate Effect On Tibetan Plateau

Posted on:2009-02-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:H F FanFull Text:PDF
GTID:1100360245481182Subject:Physical geography
Abstract/Summary:PDF Full Text Request
IPCC (Intergovernmental Panel on climate change) at Paris presented a record stating that global warming trend has become clear and it has been widely accepted that human activities are the dominant factors. The latest studies show that the significant increase trends of the atmosphere carbon dioxide concentration and the temperature can only be observed in the climatic records of early Cenozoic. Therefore, amounts of interest s have been invoked in the driving forces of past climate changes and especially those of geologically abrupt warming events; the knowledge about the driving forces, processes and the influences of past climate change can help us better understand the current climatic changes. The Tibetan Plateau, with an average elevation of 4500 m, account for a quarter of China's land. It is the highest plateau on the earth, and known as "the roof of the World". It attracts many scholars to explore tirelessly and concerned deeply because it's young geological history, unique geography environment and complex biogeographic realm, especially about the plateau uplift and the climate vary. In order to investigate the temperature changes at different altitudes on Tibet Plateau area and the relationship of temperature vary with elevation height, latitude and longitude; the different temperature vary in different Tibetan Plateau area; Tibetan Plateau influence to the surrounding area, we applied advanced data analysis and graphic software to deal with the average month ground temperature and precipitation data in the three period: 1936 to 1964,1965 to 1977,1978 to 2000.The chief results obtained in this study as follow:(1) Under conditions of global climatic changing warming, the area in Tibetan plateau, comparing to the global climate, in which the temperature rising is more tantivy. From 1965 to 1977,the global climatic changed little and stabilization. Then it became uplifted fast in 1978 to 2000, besides, the trend of the air temperature ascending extent is larger in the former than the latter time in Tibetan plateau. The climatic changing warming is earlier than other places, which might prove the theory that Tibetan plateau is a amplifier of global climatic changing(Pan Baotian et al,1995,1996)(2) The temperature and elevation in Yangtze River valley of which is located in the eastern of Tibetan Plateau have the relationship of T=-0.0046×H+18.2725 (T represents average temperature, H represents elevation); (3) Three relationships were obtained by processing temperature data collected from 1206 observatories, they are: T= -0.0041×H+16.91, T= -0.0020×H-0.3210×N+26.24, T= - 0.0020×H-0.2692×N-0.0216×E+26.21 (T represents average temperature, H represents elevation, N represents latitude, E represents longitude). There are 342 observatories could pass the 0.01confidence testing of the first relationship, which mainly located in the eastern of the Tibetan Plateau; there are 332 observatories could pass the 0.01confidence testing of the second relationship, which mainly located in the southeast of the Tibetan Plateau; there are 251 observatories could pass the 0.01confidence testing of the third relationship, which mainly located in the northeast of the Tibetan Plateau. The other 281 observatories chiefly situated on the Tibetan Plateau. This phenomenon probably link to the plateau topography, but the cause need further investigation.(4) The average temperature was increasing from past 23 years in the Tibetan Plateau and surrounding area and the extent is linked to the elevation. The annual spring temperature increase rate in the elevation of less than 2500m, 2500m to 3000m, 3000m to 3500m, 3500m to 4000m, more than 4000m are 0.033, 0.035, 0.036, 0.040, 0.046℃/a, respectively; and in winter are 0.038,0.039,0.030,0.031,0.024℃/a, respectively; and summer are 0.024,0.033,0.031,0.020,0.038℃/a, annual average values are 0.034,0.039,0.037,0.032,0.036℃/a. In general, the change amplitude of temperature above 2500m of the plateau is more than the elevation below 2500m. However, the change amplitude of temperature shows decreasing trend above 2500m. The rate of warming trend increase accompany with the elevation rising in spring, whereas the rate of warming decreases accompany with the elevation rising in winter. The rate of warming trend of winter is greater than summer in the same elevation (the elevation of above 4000 m is exception); summer temperature in 1981 is abnormally high and winter temperature in 1983 is abnormally low.(5) Generally speaking the precipitation is increasing in recent 36 years, but the increasing extent exists some differences in different seasons, different regions. The precipitation increased obviously and the amplitudes are 8.20mm and 11.23m. However the precipitation is decreasing distinctly in the northeast of the Tibetan Plateau, such as the Dachaidan observatories which the precipitation varies are 3.76mm, -14.86mm, -1.09mm, 0.67mm in spring, summer, autumn and winter, respectively. Although the precipitations in spring and winter had increased, the total annual values also decreased and the amount is -11.52mm. The precipitation of the rivers and valleys in the southeast of the plateau exhibited distinctly increasing trend, such as Gong Mountain and Bomi Mountain which are 166.35mm and 145.95mm respectively. We tentatively identify the June to September as the flood season and its distribution characteristics are precipitation increased in the eastern Qinghai region and reduce in the south, whereas the precipitation in the south of Tibetan Plateau, southeast and North Tibet Plateau increased obviously. Since the 1980, the flood season increased obviously in the Tibetan especially in the Yarlungzangbo River, whereas precipitation significantly reduced in the eastern part of Qinghai Rivers particularly in the source area of the river. Another characteristic of the plateau precipitation is the inverse change trend in the North and South from which basically along with the Tanggula Mountain. According to this boundary, Tibetan Plateau could be divided into two regions—west area (Tibetan area) and north area (Qinghai area). In Qinghai area, the precipitation in 1970 is more than in 1980 and the turning point is 1990. Tibetan area displayed unique variation in winter and spring. In the late 1970s to the 1990s the precipitation became more. Actually, flood season precipitation represents the annual rainfall changes. Precipitation in Qinghai and Tibetan Plateau in flood season has inverse relationship but this relationship is not strong just because the difference between the two mutations and rainfall in Qinghai area is lag than Tibetan area.(6) Climate variation characteristics of Zigetongco region are described as follow: (a) the lake area of Zigetangco is increasing gradually from 1970,1977,1992, 2001, 2006 years if the annual change of the lake area is not considered, (b) the annual temperature of the Nagqu, Bangor and Anduo areas increased significantly since 1970 to 2000 years, the temperature change extent are 0.45℃/ 10 a, 0.32℃/ 10 a and 0.16℃/10a, respectively. The average annual temperature is higher in summer but did not change significantly in winter. The precipitation in summer and winter of the three observatories has also increased obviously.Climate changes probably have certain impacts on the Lake area variation. The lake area of the Zigetangco expanded gradually these years and it might be due to the precipitation increased and evaporation decreased in summer and winter.
Keywords/Search Tags:Tibet Plateau, climate effect, temperature, precipitation Atmospheric circulation, Dynamic effect, thermodynamic effect, monsoon
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