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Chen S.,Institute of Arid Meteorology | Guo J.,Meteorological Bureau of Baiyin | Wu C.,Meteorological Bureau of Baiyin
Journal of Natural Disasters | Year: 2015

By use of nearly 50a precipitation data and NECP data of 131 stations in southwest and south China and linear trend analysis, synthesis analysis, wavelet analysis, as well as power spectrum anlysis methods, the winter drought was divided into no drought, light drought, medium drought, heavy drought and special heary drought five grades based on season-scaled precipitation anomaly percentage. The results show that; in this area, each grade of drought has strengthening tendency from east to west, heavy drought and special heavy drought areas concentrate in southwestern Sichuan-Yunnan, southern Guangdong. Each grade drought climate trends are not obvious. The year 1963 was the heaviest year of drought in 50 years, followed by 1969, 2009 and 1974. But at the end of 2010, drought area increased and the intensity strengthened. Each grade of drought has 2 ∼ 3a period, special heavy drought has 6a significant period; In high frequency drought area, the consecutive drought frequency is also high. With the increase in the number of consecutive drought year, the distribution range is reduced.

Chen S.Y.,Institute of Arid Meteorology | Shi Y.Y.,Meteorological Bureau of Baiyin | Guo Y.Z.,Meteorological Bureau of Baiyin | Zheng Y.X.,Meteorological Bureau of Baiyin
Journal of Arid Land | Year: 2010

We analyzed the 1961-2006 mean surface air temperature data of 138 stations in China's northwest arid and semi-arid areas (CNASA), to measure climate change in terms of annual mean air temperature changes. We used methods of linear regression analysis, multinomial fitting, Empirical Orthogonal Function (EOF), Rotated Empirical Orthogonal Function (REOF), Mann-Kendall, Glide T-examination, wavelet analysis and power spectrum analysis. The results show that (1) the warming rate of the annual mean air temperature in CNASA was 0.35°C/10a during the 1961-2006 study period. Some places in the west part of Xinjiang and east part of the Qinghai plateau, which is impacted by the terrain of leeward slope, exhibit smaller increasing trends. However, the majority of region has shown distinct warming in line with general global warming; (2) The standard deviation of the annual mean temperature distribution is non-uniform. The south Xinjiang and east Qinghai-south Gansu areas show relatively small standard deviations, but the inter-annual variation in annual mean air temperature in the greater part of the region is high; (3) Inner Mongolia, Shaanxi, Gansu, Ningxia and Tarim Basin are the areas where the temperature changes are most sensitive to the environment. The degree of uniformity in annual mean air temperature increase is higher in the arid and semi-arid area. From the early 1970s, the trend in temperature changed from a decrease to an increase, and there was a marked increase in mean temperature in 1986. After that mean temperature went through a period of rapid increase. The entire area's 10 hottest years all occurred in or since the 1990s, and 90% of various sub-districts' hottest years also occurred after 1990. The process of temperature change appears to have a roughly 5-year and a 10-year cycle; (4) Annual mean air temperature variation has regional differences. In Inner Mongolia-Xinjiang and Shaanxi- Gansu-Ningxia-Qinghai areas, the temperature variation in their northern areas was very different from that in their southern areas; (5) Using the REOF method we divided the region into 4 sub-regions: the Northern region, the Plateau region, the Southern Xinjiang region and the Eastern region. The region's annual mean air temperature transition has regional differences. The Plateau and Southern Xinjiang regions got warmer steadily without any obvious acceleration in the rate of warming. The Northern region's warming started about 5-years earlier than that of the low latitude Eastern region. The 'Startup region' of the Qinghai-Tibet Plateau, appears to undergo temperature changes 3 to 10 years earlier than the other regions, and exhibits inter-decadal variations 1 to 2 years ahead of the other regions.

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