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A Multi-scale Spatiotemporal Analysis Of Extreme High Temperature Events In China Based On Multiple Indices

Posted on:2017-02-15Degree:MasterType:Thesis
Country:ChinaCandidate:M ZhangFull Text:PDF
GTID:2180330485462768Subject:Physical geography
Abstract/Summary:PDF Full Text Request
Global warming has caused increases in extreme high temperature events, which leads to profound impacts on sustainability of human society and ecosystem. Particularly, China may increasingly suffer extreme high temperature events due to the ageing, high density and migration of population, the increasing social wealth and the relatively insufficient measures for adapting to climate change. Therefore, it is necessary to properly identify the spatial and temporal variations of extreme high temperature events for a comprehensive understanding of the challenges and opportunities in adapting to and mitigating of climate change in China. This paper presents a comprehensive analysis based on daily maximum temperature of 494 meteorological stations during 1961–2014. It uses both the percentile-based threshold(TX90) and fixed threshold(35 °C, 37 °C and 40 °C) to construct indicators of high temperature’s strength and frequency and heat wave’s frequency, intensity, duration, amplitude and occurrence days. This analysis is performed at both station scale and region scale. The main findings and conclusions are as follows:(1) The spatial patterns of high temperature events and heat waves were investigated. As for high temperature event, percentile-based extreme high temperature frequencies mainly concentrated in 7 to 15 times per year, and displayed in the Xinxiang autonomous region, the central region, the southwest and northeast China is relatively low, while there are significant regional differences in intensity. Strongest intensity was located in Xinjiang province and the eastern monsoon region, followed by north China excluding Xinjiang region; the intensity of the Qinghai-Tibet plateau is minimal. Using fixed thresholds, however, high temperature events cover less areas and no high temperature events occurred in Qinghai-Tibet plateau. Fixed-threshold high temperature events mainly have high values in Xinjiang province and the middle and lower reaches of the Yangtze River basin and Yellow River basin. Heat waves occur across the country Using percentile-based threshold, while the fixed threshold heat waves are mainly distributed in Xinxiang province and east China’s Yangtze river and in the middle and lower reaches of the Yellow River basin. The average intensity of heat waves is greater in north China than south China using fixed thresholds while this relation is reversed when using percentile-based threshold.(2) The trends of high temperature events and heat waves were examined from a spatial perspective. As for high temperature events, the intensity of percentile-based high temperature event displayed a decreasing trend in the Xinjiang province and the eastern China while the rest stations show an increasing trend; the intensity and frequency of fixed-threshold high temperature events as well as the percentile-based threshold frequency declined in central China and Xinjiang province and increased in the eastern monsoon region and Xinjiang autonomous region. As for heat waves, percentile-based heat waves indexes showed significantly upward trends in the Tibetan plateau and a downward trend about heat intensity and amplitude in the eastern monsoon region. There are no fixed threshold heatwaves on the Tibetan plateau; the heat wave indexes show a downward trend at lots of central stations. In a word, percentile based heat wave frequency increased faster in the northern region than southeastern coast at the regional scale, while fixed threshold heatwaves show opposite trend.(3) The regional differences in trends of high temperature events and heat waves were explored. Overall, high temperature events and heat waves are on a rising trend in the whole nation, northern China and the southeast coastal area of China and a declining trend in the central China. The heat wave frequency and heat wave days are increasing in the north, southeast coastal area and the entire China, while a decreasing trend is revealed in the central region. The duration of percentile-based heat waves are increasing across the country, north and southeast coastal area, and decreasing in the central region; in contrast, the duration of fixed-threshold heat waves are increasing in the southeast coastal areas and decreasing in others. The intensity and amplitude of percentile-based heat waves are increasing across the country and three typical areas, while their fixed-threshold counterparts are increasing across the country, north and southeast coastal area, and decreasing in the central region.(4) “U-shape” temperal changes in high temperature events and heat waves were revealed, which was further used for policy implications. On the whole, the time series of high temperature events and heat waves in typical regions and the entire China have three phases and display a typical "U-shape" structure characteristics. The three phases can be identified as 1961-1979, 1980-1989 and 1979-1980. High temperature events and heat waves largely declined during 1961-1979, remained relatively stable during 1980-1989, and accelerated during 1990-2014. “Warming hole” and “hiatus” would not reduce China’s national scale and regional scale of the probability of extreme high temperature events. Despite the current thought since 1998, global warming stagnation, but the 1990-2014 national and three typical area, extreme high temperature and heat waves was accelerated. Climate change and human activities may lead to increasing heat wave frequency and heat waves days in northern China and southeast coastal areas; moreover, heat wave’s amplitude is bigger and bigger.These results indicate that the spatiotemporal analyses of high temperature event and heat waves depend on their definitions and specific thresholds. Percentile-based threshold high temperature events and heat waves distributed more widely in China, which displayed a more evenly spatial distribution. Fixed-threshold high temperature events and heat waves showed significant variations among diiferent regions. Taking into account the definition of percentile-based threshold and fixed threshold, the(right) tail variation percentile-based threshold temperature may be more suitable for describing the frequency distribution of the station, but it is difficult to reflect the pressure and impacts on the socio-economic system. The fixed threshold temperature can characterize virulence global temperature changes according to uniform standards, more suitable for the analysis of climate change and pressure on social economy. These results reveal the frequency and intensity of high temperature events and heat waves have accelerated during 1990–2014, which deserves more attention and analyses. If this trend continues, it will have a serious impact on China’s socio-economic and natural environment, health and safety.
Keywords/Search Tags:China, Extreme high temperature, heat wave, spatio-temporal distribution, region time series
PDF Full Text Request
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