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Lhasa, China

Du J.,Institute of Plateau Meteorology | Du J.,Tibet Climatic Center | Ma P.,Tibet Climatic Center | Pan D.,Lhasa Meteorological Service of Tibet
Dili Xuebao/Acta Geographica Sinica | Year: 2016

Based on 6- hourly (02:00, 08:00, 14 00 and 20:00 Bejing time (BJT)) air temperature data of 38 meteorological stations over Tibet from 1981 to 2014, the spatialtemporal distribution and climate abrupt characteristics of air temperature are analyzed by using the methods including linear regression and Mann- Kendall test. Also, the correlation between the change rates of surface air temperature and latitude (longitude, and altitude) is discussed. The results showed that, the seasonal air temperature in Tibet exhibits unanimously increasing trend with a rate of 0.14-0.80℃/10a during the past 34 years, and the most significant increase occurred in winter. In terms of the rate per decade for the 6- hourly air temperature observations, 08:00 BJT during summer experienced the highest increasing rate, while 14:00 BJT showed the highest values for the other three seasons. The maximum rate for the increasing air temperature ranges from 0.36℃/10a (P < 0.001) to 0.94℃/10a (P < 0.001). Among all the 38 stations, there were only 32% (about 12) showing the peak time with the highest rate of changes at 08:00 BJT air temperature, which are predominantly located in much of Qamdo, Ngari prefecture and at weather stations such as Nagqu, Lhasa and Xigazê, while the rest of weather stations showed the highest increasing rate at 14:00 BJT. In spring and autumn, as the increasing rate was related to longitude, it has a larger rate in western than that in eastern Tibet. In winter, the highest increasing rate of air temperature occurred in the regions with higher altitudes and latitudes, and the higher increasing rate of air temperature was observed at higher latitudes in summer. As for the decadal characteristics of 6- hourly air temperature, the 1980s experienced negative anomalies, compared with positive anomalies in the first decade of the 21st century. Additionally, it was found with abrupt change test that at the annual and seasonal scales most of hourly air temperatures have abrupt change. For instance, the abrupt change of all four hourly air temperatures in summer occurred in the first decade of the 21st century. In winter, the abrupt change of air temperature at 02:00 and 08:00 BJT occurred in the late 1990s, while that at 14:00 and 20:00 BJT was found in the first 10 years of the 21st century. As can be seen in the article, many factors such as topography, various meteorological elements in the plateau and the atmospheric circulation play important roles in the surface air temperature change in Tibet. © 2016, Science Press. All right reserved.

Bi X.,CAS Research Center for Eco Environmental Sciences | Bi X.,University of Chinese Academy of Sciences | Luo W.,CAS Research Center for Eco Environmental Sciences | Gao J.,CAS Research Center for Eco Environmental Sciences | And 10 more authors.
Science of the Total Environment | Year: 2016

The Central Himalayas are not only a natural boundary between China and Nepal but also a natural barrier for transport of air masses from South Asia. In this study, 99 samples of surface soil were collected from five regions of Nepal on the southern side of the Central Himalayas, and 65 samples of surface soil were obtained from the northern side on the edge of the Tibetan Plateau, China (TPC). Concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils were measured to determine their distribution, potential for accumulation, and sources, as well as risks to humans and the environment. Mean concentrations of σ16PAHs were 2.4 × 102 and 3.3 × 102 ng/g dry mass (dm) in soils collected from the TPC and Nepal, respectively. Significant correlations between concentrations of lower molecular weight PAHs (LMW-PAHs) in soils and altitude were found. Total organic carbon (TOC) in soil was positively but weakly correlated with concentrations of PAHs in the study area, which suggested little role of TOC in adsorption of PAHs. The cities of Kathmandu and Pokhara in Nepal and Nyemo (especially Zhangmu Port), Shigatse, and Lhasa on the TPC, were areas with relatively great concentrations of PAHs in soils. The main sources of PAHs identified by positive matrix factorization were emissions from motor vehicles and combustion of coal and biomass in the Central Himalayas. Calculated total benzo[a]pyrene potency equivalents of 0.23-44 ng/g dm and index of additive cancer risk of 3.8 × 10-3-9.2 × 10-1 indicated that PAHs in almost all soils investigated posed de minimis risk of additional cancer to residents via direct contact and had no significant risk of additional cancers through consumption of potable water. Mean risk quotient values indicated that 39% of soils had a slight risk to wildlife and the ambient environment of the Central Himalayas. © 2016 Elsevier B.V.

Du J.,Institute of Plateau Meteorology | Du J.,Tibet Climatic Center | Lu H.,Tibet Climatic Center | Jian J.,Shannan Meteorological Service of Tibet
Acta Geographica Sinica | Year: 2013

Based on homogeneity-adjusted daily temperature (maximum, minimum and average) data of 18 stations, spatial and temporal changes of extreme temperature events over Tibet were analyzed for the period 1961-2010. The result shows that the number of frost days and ice days reduced significantly, with the most significant reduction in northern Tibet for ice days, but more extensively across the autonomous region for frost days. The length of growing season (GSL) presented a statistically significant increasing trend at a rate of 4.71 d/10a, especially in Lhasa and Zedang. The extra-maximum air temperature (TXx) and extra-minimum air temperature (TNn) generally increased. TXx significantly increased along the east section of the Yarlung Zangbo River and in Nagqu Prefecture, and decreased at the southern edge of Tibet, while TNn significantly increased across the region of Tibet, especially during 1981-2010 with a rate of 1.06°C/10a. Significant reduction at a rate of 9.38 d/10a (4.96 d/10a) occurred on cool nights (days), and significant increase at a rate of 10.99 d/ 10a (6.72 d/10 a) occurred for warm nights (TN90p) (days (TX90p)). There is a close correlation between the trends of most extreme temperature indices and altitude, i.e., positive correlations between altitude and TNn, negative correlations between altitude and TXx, TX90p, TN90p and GSL. In terms of decadal variations, TXx, TNn and other warm indices showed an increasing trend, while the cold indices and GSL decreased. It is also found that the abrupt change points of the TNn, warm (cool) nights and GSL were mainly observed before the mid-1990s, while frost days, ice days and warm (cool) days occurred in the early 2000s. In most cases, the linear trend magnitudes of extreme air temperature indices in Tibet were larger than those in the whole country, Tibetan Plateau and its surrounding areas (Qinghai Province, Hengduan Mountains), which show that the extreme air temperature indices response are more sensitive to the regional warming.

Du J.,Institute of Plateau Meteorology | Du J.,Tibet Climatic Center | Yang Z.,Tibet Climatic Center | Shi L.,Tibet Climatic Center | Ma P.,Tibet Climatic Center
Acta Geographica Sinica | Year: 2011

According to the China national standard, the warm winter is classified into two groups by space and intensity grades. In the space group the warm winter is divided into two spatial grades as single station warm winter, and regional warm winter. In the intensity group, there are two grades as weak warm winter (warm winter) and strong warm winter. Average winter air temperature is divided into three probability categories to define the threshold of warm winter for single station and its warm winter intensity. Then the division criteria for regional winter warm intensity are calculated according to percentile rank of warm winter stations. In accordance with this standard, the grade of single station and regional cold winter are determined. On the basis of the division method for cold and warm winter, the characteristics of cold and warm winter from 1961 to 2010 over Tibet are analyzed. The results show that the mean temperature in winter has increased over Tibet with a rate of (0.29-1.04)°C/10a in recent half century, and the maximum value is in Bangoin. Especially in recent 20 years (1991-2010), the warming amplitude becomes stronger with a rate of (0.73-2.36)°C/10a. Regional warm winter index has an obvious rising trend at a decadal rate of 16%, which is higher than that in Northeast China, North China and Northwest China. Frequency of single station warm winter is 32%-52% with 6%-26% of strong warm winters. There are 21 regional warm winter years over the 50 years with 10 strong warm winters, and there are more occurrences of warm winter in the 2000s, while the most extensive and strongest of regional warm winter occurred in 2006 and 2009. The results also show that the frequency of single station cold winter is 18%-40% with 2%-20% of strong cold winters, and that regional cold winter index has a decreasing trend at a decadal rate of 12%. There are 16 regional cold winter years over the 50 years with 8 strong cold winters, and more occurrences of cold winter was observed in the 1960s. Additionally, the year 1962 witnessed the most extensive and strongest regional cold winter, followed by 1968 and 1983.

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