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The Spatial And Temporal Characteristics Of Temperature And Precipitation In Arid And Semi-Arid Regions Of China

Posted on:2015-02-17Degree:MasterType:Thesis
Country:ChinaCandidate:J J RanFull Text:PDF
GTID:2250330431451101Subject:Science of meteorology
Abstract/Summary:PDF Full Text Request
Using the each site’s monthly mean temperature data, monthly precipitation data, daily precipitation data and NECP/NCAR monthly mean reanalysis data, the temperature, the annual precipitation and the space-time distribution features of extreme precipitation events in arid and arid areas of China are analyzed in detail. And the atmospheric circulation are synthetic analysis, which tried to analyze the physical mechanisms of the change. The main three conclusions are as follows:1.We have detailedly investigated the seasonal and regional characteristics of the warming in China by analyzing55-year monthly homogenization surface air temperature of713stations from the National Climate Center of China. In particular, we analyzed the atmospheric circulation before and after cold season warming of arid and semi-arid region. The interannual variation shows that warming began in the mid1980s, and increased fast in the1990s, then gradually slowed down in the early21st century. The annual average warming trend in semi-arid and arid areas is1.7times that in humid and semi-humid areas. As for seasonal characteristics, the warming trend during cold seasons is1.9times that during warm seasons. The warming trend is comparatively fast in arid and semi-arid areas with more than0.3℃/10a and particularly notable in the Tibet Plateau, middle inner Mongolia, northeast and north China. However, the warming trend in humid and semi-humid areas is relatively slow, in which the central and west regions is slower than east coast. The cold season temperature in arid and semi-arid areas experienced a significantly abrupt change from cold to warm at1986. A composite analysis is used here to investigate the response of the atmospheric circulation. We found that the arctic polar vortex, Eastern Asia Trough, Shallow Trough in Europe and Siberian High become weakening, and anomaly cyclonic circulation occurred, as well as abnormal southeast wind occurred in eastern of china which all could induce the warming in semi-arid and arid areas.2.Using monthly precipitation data from756stations of China from1951to2011, we analyzed the warm-season precipitation change of arid and semi-arid areas over northern China. The results indicated that precipitation of arid and semi-arid areas showed the opposite trend during the recent60years. The warm-season precipitation increased overall in arid areas with0.27mm/a and decreased in semi-arid areas with0.80mm/a. The difference existed mainly because the two regions were controlled by different circulation system, that is the arid areas by westerlies and semi-arid areas by monsoon. The composite analysis of atmospheric circulation in this two areas for years with more(less) precipitation showed that when westerly flow strengthening and southward, the water vapor of the Black Sea, the Caspian Sea and Lake Balkhash was carried to our arid region, conducive to the precipitation of this areas, and vice versa. When the East Asian summer monsoon was strong, the water vapor going westward to the central Gansu (105°E), and northward to the entire north and northeast China, the precipitation of semi-arid areas increased, and vice versa.3. The floods over arid and semiarid regions are highly associated with the number, intensity and duration of the extreme precipitation events, which also determine the number and severity of the floods and its secondary geological disasters over the regions. In this study, we analyzed the number and the characteristics of extreme precipitation events in the arid and semiarid regions, in order to provide some scientific basis for the further study. The results showed that the number of days of extreme precipitation events has increased since the21st century over the arid and semi-arid areas west of110°E, but decreased to the east of the region. The trend of extreme precipitation shows positive sign in the west and negative sign in the east of the arid and semiarid regions, in addition, the fraction of extreme precipitation changes over the total precipitation changes is over40%in most of the regions, and could reach50%or even100%to200%in some areas. The seasonal variation shows that the extreme precipitation increased in spring over the north of Mountains, southern Xinjiang, and the north of Dunhuang, Gansu and Inner Mongolia; In summer, the extreme precipitation increased dramatically over the arid and semiarid regions west of110°E; And in autumn, the extreme precipitation increased over Yulin in northern Shanxi, Erdos in Inner Mongolia, Hohhot, Baotou and some other places. Based on the above results, we also did some basic analysis on the spatial and temporal characteristics of floods over the arid and semiarid regions.
Keywords/Search Tags:Arid and semi-arid regions, Cold-season warming, Precipitation, Atmospheric circulation, Extreme precipitation event
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