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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.

PubMed | Beijing Normal University, Northwest Regional Climate Center and Peking University
Type: Journal Article | Journal: PloS one | Year: 2016

Estimating gross primary production (GPP) and net primary production (NPP) are significant important in studying carbon cycles. Using models driven by multi-source and multi-scale data is a promising approach to estimate GPP and NPP at regional and global scales. With a focus on data that are openly accessible, this paper presents a GPP and NPP model driven by remotely sensed data and meteorological data with spatial resolutions varying from 30 m to 0.25 degree and temporal resolutions ranging from 3 hours to 1 month, by integrating remote sensing techniques and eco-physiological process theories. Our model is also designed as part of the Multi-source data Synergized Quantitative (MuSyQ) Remote Sensing Production System. In the presented MuSyQ-NPP algorithm, daily GPP for a 10-day period was calculated as a product of incident photosynthetically active radiation (PAR) and its fraction absorbed by vegetation (FPAR) using a light use efficiency (LUE) model. The autotrophic respiration (Ra) was determined using eco-physiological process theories and the daily NPP was obtained as the balance between GPP and Ra. To test its feasibility at regional scales, our model was performed in an arid and semi-arid region of Heihe River Basin, China to generate daily GPP and NPP during the growing season of 2012. The results indicated that both GPP and NPP exhibit clear spatial and temporal patterns in their distribution over Heihe River Basin during the growing season due to the temperature, water and solar influx conditions. After validated against ground-based measurements, MODIS GPP product (MOD17A2H) and results reported in recent literature, we found the MuSyQ-NPP algorithm could yield an RMSE of 2.973 gC m(-2) d(-1) and an R of 0.842 when compared with ground-based GPP while an RMSE of 8.010 gC m(-2) d(-1) and an R of 0.682 can be achieved for MODIS GPP, the estimated NPP values were also well within the range of previous literature, which proved the reliability of our modelling results. This research suggested that the utilization of multi-source data with various scales would help to the establishment of an appropriate model for calculating GPP and NPP at regional scales with relatively high spatial and temporal resolution.

Han L.,Institute of Arid Meteorology | Han L.,Northwest Regional Climate Center | Han L.,Lanzhou University | Zhang Q.,Meteorology Bureau of Gansu | And 4 more authors.
Acta Geographica Sinica | Year: 2014

Drought is a meteorological disaster that causes huge losses to agricultural yields every year. This paper analyzed drought trends based on statistical disaster data, which included drought-induced areas, drought-affected areas, and lost harvests under the effects of global warming. The results showed that droughts are becoming more critical and frequent in China. The agricultural effects of drought for drought- induced areas, drought- affected areas, lost harvest areas and comprehensive loss rate increased in the last 60 years in each province of Southwest China. It is important to examine the spatial and temporal changes in the agricultural effects of drought in guiding disaster mitigation work. This paper analyzed the drought conditions in large farming areas of Southwest China, which were frequently hit by serious droughts. Total drought area ranked first in Sichuan Province, second in Guizhou Province, and third in Yunnan Province. The average annual comprehensive loss rate accounted for 3.9% in Southwest China, and increased in recent years. Drought tolerance of all provinces is related to regional climate change effects, such as temperature, precipitation, moisture, and vegetation coverage.

Jiang Y.,Meteorological Bureau of Gansu Province | Jiang Y.,Northwest Regional Climate Center | Ma P.,Northwest Regional Climate Center | Han T.,Northwest Regional Climate Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015

Using the MOD13A3 data from 2000 to 2013, Analyze the change of time and space by using the methods of maximum synthesis, trend line analysis, and Hurst index; at the same time, calculate and analyze the vegetation coverage in Hexi area with dimidiate pixel model. The result shows an obvious and overall increasing trend of the vegetation index in Hexi area, Gansu province from 2000 to 2013; the area with strong sustainable variation is the largest as a percentage of the total Hexi area, which is 18.1%, the area with strong anti-sustainable variation is only 0.2% as a percentage of the total Hexi area; the high and medium vegetation coverage areas in 2013 has increased than that in 2000,the association between the variation of high vegetation coverage area in Hexi and annual precipitation is smaller, and generally, the vegetation coverage area in Hexi, Gansu province has a subtle increasing trend. © 2015 SPIE.

Han L.,Institute of Arid Meteorology | Han L.,Northwest Regional Climate Center | Guo N.,Institute of Arid Meteorology | Li Y.,Institute of Arid Meteorology | And 2 more authors.
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

Wetland Ecosystem is one of important ecosystem in forest, ocean and wetland ecosystems. The wetland ecosystem is very important in global climate change and environmental protection. At present, remote sensing and GIS are widely applied to environmental research. In this paper, based on MODIS from 2002s to 2010s and combined with field data from 2001 to 2010, using GIS techniques and the human-machine interactive remote sensing interpretation method, which is adopted to analysis spatial statistics and avoid the lose and overlap of information, the dynamic monitoring of temporal and spatial variation of wetland ecosystem in Maqu County, Gansu Province, China was conduced. The result found that the wetland area decreased from 431.21 km2 to 183.00 km2 from 2002s to 2010s in Maqu County. The meteorological data from 1970s to 2010s was carried out and showed that warming and arid climate played important roles in the wetland degradation over Maqu County. © 2012 IEEE.

Yang Z.,Chengdu University of Information Technology | Yang Z.,Institute of Arid Meteorology | Zhang Q.,Institute of Arid Meteorology | Hao X.,Northwest Regional Climate Center
Advances in Meteorology | Year: 2016

There have been few studies conducted on the changes in actual ET over the Loess Plateau, due to the lack of reliable ET data. Based on ET data simulated by the Community Land Model, the present study analyzed the changes in ET over the Loess Plateau. The results showed the domain-average ET to have decreased in the past 31 years, at a rate of 0.78 mm year-1. ET fluctuated much more strongly in the 1990s than in the 1980s and 2000s, and, apart from in autumn, ET decreased in all seasons. In particular, ET in summer comprised about half of the annual ET trend and had the sharpest trend, dominating the interannual decline. ET also decreased more sharply in the semiarid than semihumid regions. The declining trend of ET was attributed to declining precipitation and air humidity. Locally, the ET trend was closely related to local mean annual precipitation: in areas with precipitation less than 400 mm, ET showed a decreasing trend; in areas with precipitation larger than 600 mm, ET showed an increasing trend; and in areas with precipitation in the range of 400-600 mm could be classified as a transitional zone. © 2016 Zesu Yang et al.

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.

Fang F.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Fang F.,Northwest Regional Climate Center | Guo J.,Northwest Regional Climate Center | Sun L.,Shanghai Climate Center | And 2 more authors.
Theoretical and Applied Climatology | Year: 2014

Using data collected from 22 urban and 65 rural meteorological stations in northwestern China between 1961 and 2009, this paper presents a study concerning the effects of urbanization on air temperature trends. To distinguish among the potential influences that stem from the economic development levels, population scales, and geographic environments of the cities in this region, the 49-year study period was divided into two periods: a period of less economic development, from 1961 to 1978, and a period of greater economic development, from 1979 to 2009. Each of the cities was classified as a megalopolis, large, or medium-small, depending on the population, and each was classified as a plateau, plain, or oasis city, depending on the surrounding geography. The differences in the air temperature trends between cities and the average of their rural counterparts were used to examine the warming effects of urbanization. The results of this study indicate that the magnitude of warming effects due to urbanization depends not only on a city's economic level, but also on the population scale and geographic environment of the city. The urbanization of most cities in northwestern China resulted in considerable negative warming effects during 1961-1978 but evidently positive effects during 1979-2009. The population scale of a city represents a significant factor: a city with a larger population has a stronger warming influence, regardless of whether the effect is negative or positive. Among the three geographic environments of the cities considered, plateaus and plains more significantly enhance warming effects than oases. The urban population trend has a very significant logarithm relationship with the urban temperature effect, but no clear relationships between urban temperature effects and city elevation were detected. The majority of the temperature trends, accounting for more than 60 % of the trends during 1961-2009, can be explained by natural factors, although urbanization has had some obvious effects on temperatures in northwestern China. © 2013 Springer-Verlag Wien.

Feng L.,Northwest Regional Climate Center | Feng L.,Hubei University | Wang L.,Hubei Engineering University | Gong W.,Hubei Engineering University | And 2 more authors.
Theoretical and Applied Climatology | Year: 2015

Total ultraviolet (UV) irradiation (290–400 nm) observed at Sanya (SY, 109°28′E, 18°13′N), China during 2005–2012 was used to investigate UV variability and its relationship with global solar radiation under various sky conditions in Southern China for the first time. Monthly mean daily UV irradiation generally increased from 0.585 MJ m−2 in December to 0.965 MJ m−2 in July with annual mean value being about 0.767 MJ m−2. Monthly mean daily FUV (ratio of UV to G) changed from 4.19 % in December to 4.68 % in July with annual mean being about 4.45 % at SY, China. By analyzing the dependences of hourly UV irradiation on optical air mass, clearness index, and cosine of solar zenith angle, respectively, under various sky conditions, three different UV estimation equations have been introduced and validated at SY, Inner Mongolia, and Lhasa. The statistical results indicated that estimation Eq. 3 (based on clearness index and cosine of solar zenith angle) produced the most satisfied estimates at Sanya: mean bias error, mean absolute bias error, and root-mean-square error were only −0.72 % (−0.23 %), 4.67 % (4.45 %), and 6.43 % (5.88 %), respectively, at hourly (daily) basis. Hourly and daily UV irradiation during 1992–2012 were then reconstructed, it was discovered that UV irradiation increased slightly during the study period and the most significant increases (0.904 MJ m−2 day−1 decade−1) were observed in summer. © 2014, Springer-Verlag Wien.

Wang L.,Hubei Engineering University | Wang L.,Wuhan University | Gong W.,Hubei Engineering University | Gong W.,Wuhan University | And 3 more authors.
International Journal of Climatology | Year: 2015

Ultraviolet radiation (UV) observed at Fukang (FK), China from 2004 to 2012 was used to investigate UV variability and its relationship with global solar radiation (G) under various sky conditions in Northwest China. Clearness index (Kt) was used for characterizing the sky conditions and UV model development, it was discovered that clear skies were the dominated sky conditions (48.72%), followed by partly cloudy (32.56%) and overcast (18.72%) skies. Daily FUV (fraction of UV to G) increased from November to June with an annual mean of 4.00% at FK. Meanwhile, an efficient all-sky UV model under any sky conditions has been proposed by investigating the dependence of hourly UV irradiations on Kt and cosine of solar zenith angle μ The model was assessed through the statistical indices: mean bias error (MBE), mean absolute bias error (MABE) and root mean square error (RMSE) whose values were 1.27 (-0.24), 4.64 (4.56) and 6.26% (6.14%), respectively at hourly (daily) basis. The model has also been tested at three other sites with distinctly different climates in China. Finally, daily UV radiation during 1961-2012 in Northwest China was reconstructed and annual mean daily UV irradiation was about 0.603MJm-2d-1. UV decreased at 0.62KJm-2d-1decade-1 during the whole study period and the decreases were sharpest in spring (3.28KJm-2d-1decade-1), however, there was an increasing trend at the rate of 2.16KJm-2d-1year-1 since 1991. © 2015 Royal Meteorological Society.

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