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Jiang Y.,Northwest Regional Climate Center | Ming J.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Ma P.,National Climate Center | Wang P.,National Climate Center | Du Z.,CAS Institute of Atmospheric Physics
Geomatics, Natural Hazards and Risk | Year: 2016

Based on MODIS data, we analyzed the spatial distribution and the intra- and inter-annual variations of the snow cover in the Qilian Mountains. In addition to discussing regional climate, we discussed the reasons for the snow cover pattern variations. The spatial distribution of the snow cover in the Qilian Mountains is uneven, and the snow cover in the west is significantly greater than that in the east. The difference in the intra-annual variations of the snow cover at different altitudes is large, and the general seasonal cycle exhibits two maxima and one minimum. The snow cover and precipitation in the Qilian Mountains were consistently increasing from 2000 to 2005, but they generally decreased from 2008 to 2013. The influences of temperature, wind speeds and precipitations on snow cover variation at different altitudes vary greatly, with the snow cover being more sensitive to precipitation in the winter, while temperature and precipitation are the major factors that affect the snow cover in the spring. © 2016 The Author(s). Published by Taylor & Francis. Source


Liu H.-L.,Zhangye Meteorological Bureau | Zhang Q.,Institute of Arid Meteorology | Zhang J.-G.,Zhangye Middle School | Guo J.-Q.,Northwest Regional Climate Center | Wang S.,Jinta County Meteorological Bureau
Chinese Physics B | Year: 2015

In this study, we analyze spring precipitation from 92 meteorological stations spanning between 1961 and 2012 to understand temporal-spatial variability and change of spring precipitation over Southwest China. Various analysis methods are used for different purposes, including empirical orthogonal function (EOF) analysis and rotated EOF (REOF) for analyzing spatial structure change of precipitation anomaly, and the Mann-Kendall testing method to determine whether there were abrupt changes during the analyzed time span. We find that the first spatial mode of the precipitation has a domain uniform structure; the second is dominated by a spatial dipole; and the third contains five variability centers. The 2000s is the decade with the largest amount of precipitation while the 1990s is the decade with the smallest amount of precipitation. The year-to-year difference of that region is large: the amount of the largest precipitation year doubles that of the smallest precipitation year. We also find that spring precipitation in Southwest China experienced a few abrupt changes: a sudden increase at 1966, a sudden decrease at 1979, and a sudden increase at 1995. We speculate that the spring precipitation will increase gradually in the next two decades. © 2015 Chinese Physical Society and IOP Publishing Ltd. Source


Wang L.,Hubei Engineering University | Wang L.,Collaborative Innovation Center for Geospatial Technology | Wang L.,Hubei University | Gong W.,Hubei Engineering University | And 6 more authors.
Energy | Year: 2014

Measurements of ultraviolet (UV) radiation at 38 stations from Chinese Ecosystem Research Network during 2006-2012 were used for reconstructing the historical UV levels in China for the first time. UV models were introduced by analyzing the dependence of UV irradiation on clearness index (Kt) and cosine of solar zenith angle under any sky conditions in each station. Mean bias error (MBE), mean-absolute bias error (MABE) and root-mean-square error (RMSE) were used for assessing the model performance; relative differences between UV estimates and measurements were generally lower than 10% at most stations, which indicated that our all-sky UV models can produce acceptable estimates in China. Long-term UV values during 1961-2012 were then reconstructed for investigating the spatiotemporal characteristics of UV radiation in China based on daily global solar radiation (G) at 115 meteorological stations from China Meteorological Administration. Annual mean daily UV radiation ranged from 0.55MJm-2d-1 to 0.65MJm-2d-1 with average value being about 0.61MJm-2d-1. It was also discovered that UV radiation decreased slightly at about -2.72kJm-2d-1 per decade during the study period and there was an increasing trend since 1991 (0.7kJm-2d-1 per year). © 2014 Elsevier Ltd. Source


Zhang T.,Northwest Normal University | Zhang B.,Northwest Normal University | Wang Y.,Northwest Normal University | Wang Y.,Northwest Regional Climate Center | And 4 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013

The Shiyang River Basin in Gansu Province is located in a semiarid area of northwestern China. In the context of global warming, the intensity and frequency of the drought in the area have experienced significant changes, which brings serious influences to agriculture in the area. The area of the drought in Shiyang River Basin was expanding in the past 50 years. So the drought has become one of the key and hot topics in climate change research, especially in a semiarid area of northwestern China in recent year, and it is necessary to choose a more effective method to analyze temporal and spatial distribution of drought. Based on the observed data of 5 meteorological stations from 1962 to 2010, the method of a series of mathematical statistic theory, GIS spatial analysis techniques and a composite index (CI) of the meteorological drought was applied to analyze the temporal and spatial characteristics of the drought in the area. According to the national standard "Classification of Meteorological Drought" (GB/ T20481-2006), CI was calculated by using the standard precipitation index of the last 30 days (equivalent to monthly scale), the last 90 days (equivalent to seasonal scale) and the relative moisture index of the last 30 days. According to the day-to-day CI index, the drought process of the stations and the drought events of different periods during the recent 50 years were calculated, and the occurrence frequency, coverage area intensity, and annual mean days of the drought in each station were analyzed to reveal the temporal and spatial pattern of meteorological droughts in the Shiyang River Basin. The results are as follows: (1)The seasonal occurrence frequencies of the meteorological drought in the area generally decreased from north to south but it was also different. The highest occurrence frequency was in summer, and the lowest was in winter; The minimum frequency in four seasons all occurred in the Wushaoling Station. However, the maximum in spring, summer and winter was observed in the Minqin Station with exception of the Wuwei Station in autumn. (2) The large-area drought in the Shiyang River Basin occurred mostly in summer and autumn but the least one in winter during 1962-2010. Meanwhile, there are 22 years and 11years of drought in summer and autumn, respectively,whereas there is 3 years in winter. (3) The drought days of different grades which was negatively correlative with precipitation distribution reduced from north to south in general, and were higher in summer and lower in winter in the Shiyang River Basin. (4) In the Shiyang River Basin, drought is mainly controlled by the Eastern Asian Monsoon and Southwest Monsoon, while the runoff factors should also be considered. This study can reflecet the fact and provide a reference for developing appropriate measures to reduce droughts in the Shiyang River Basin. Source


Hao X.-C.,Northwest Regional Climate Center | Hao X.-C.,Institute of Arid Meteorology | Zhang Q.,Institute of Arid Meteorology | Zhang Q.,Lanzhou University | Yang Z.-S.,Lanzhou University
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2016

There are few quantitative researches focused on the influence of inhomogeneous land surface condition on sensible heat fluxes measured by Large Aperture Scintillometer (LAS) and Eddy Covariance System (ECS) at present. In this paper, based on the observed land surface process data in two prevailing wind directions (E-SE and SW-W) at Qingyang site in the Loess Plateau during June and July 2012, firstly, a quantitative index representing the degree of land surface inhomogeneity was established, and then an analysis was made of the relationship between surface inhomogeneity and surface temperature variability and its influence on the difference between LAS and ECS measured sensible heat fluxes. Results showed that the land surface inhomogeneity η had a good correlation with surface temperature variability г with a correlation coefficient up to 0.566, indicating that η can well represent land surface inhomogeneity. η also had a good consistency with the difference between LAS and ECS measured sensible heat fluxes (HLAS-HECS), its correlation coefficient being up to 0.634. η significantly influenced the difference between LAS and ECS measured sensible heat fluxes. The more inhomogeneous η was, the greater HLAS-HECS was. For the two prevailing wind directions, η had a correlation coefficient of 0.430 with HLAS-HECS in E-SE wind direction, the fitting coefficient being 1.279; η had a correlation coefficient of 0.680 with HLAS-HECS in SW-W wind direction, the fitting coefficient being 1.297. LAS and ECS measured sensible heat fluxes will have a greater difference when the influence of land surface inhomogeneity is larger. © 2016, Science Press. All right reserved. Source

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