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Yang F.,Institute of Arid Meteorology | Yang F.,CAS Institute of Botany | Zhou G.,CAS Institute of Botany | Zhou G.,Chinese Academy of Meteorological Sciences
PLoS ONE | Year: 2013

Arid grassland ecosystems have significant interannual variation in carbon exchange; however, it is unclear how environmental factors influence carbon exchange in different hydrological years. In this study, the eddy covariance technique was used to investigate the seasonal and interannual variability of CO2 flux over a temperate desert steppe in Inner Mongolia, China from 2008 to 2010. The amounts and times of precipitation varied significantly throughout the study period. The precipitation in 2009 (186.4 mm) was close to the long-term average (183.9±47.6 mm), while the precipitation in 2008 (136.3 mm) and 2010 (141.3 mm) was approximately a quarter below the long-term average. The temperate desert steppe showed carbon neutrality for atmospheric CO2 throughout the study period, with a net ecosystem carbon dioxide exchange (NEE) of -7.2, -22.9, and 26.0 g C m-2 yr-1 in 2008, 2009, and 2010, not significantly different from zero. The ecosystem gained more carbon in 2009 compared to other two relatively dry years, while there was significant difference in carbon uptake between 2008 and 2010, although both years recorded similar annual precipitation. The results suggest that summer precipitation is a key factor determining annual NEE. The apparent quantum yield and saturation value of NEE (NEEsat) and the temperature sensitivity coefficient of ecosystem respiration (Reco) exhibited significant variations. The values of NEEsat were -2.6, -2.9, and -1.4 μmol CO2 m-2 s-1 in 2008, 2009, and 2010, respectively. Drought suppressed both the gross primary production (GPP) and Reco, and the drought sensitivity of GPP was greater than that of Reco. The soil water content sensitivity of GPP was high during the dry year of 2008 with limited soil moisture availability. Our results suggest the carbon balance of this temperate desert steppe was not only sensitive to total annual precipitation, but also to its seasonal distribution. © 2013 Yang, Zhou.

Zhang Q.,Institute of Arid Meteorology | Sun Z.-X.,Institute of Arid Meteorology | Sun Z.-X.,Institute of Plateau Meteorology | Wang S.,Institute of Arid Meteorology
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2011

By using the long-term integrated data of a variety of land-surface physical quantities observed over the Loess Plateau, based on analyzing the basic characteristics of soil temperature and soil moisture, the variation characteristics of main land-surface physical quantities of land-surface radiation components, land-surface energy components, surface albedo and Bowen ratio are systematically analyzed. The distribution of margin of land-surface energy unbalance is discussed. It is found that the characteristics of the land-surface physical quantities over the Loess Plateau are more different than in other regions. Especially the downward propagation of daily soil temperature, "wet layer" at 30 cm below the soil surface, asymmetrical "V"-type daily variation structure of surface albedo, bimodal distribution of sensible heat flux, the different phase of energy balance components and large margin of land-surface energy unbalance are all the new understanding of characteristics of land-surface physical quantities.

Xiao G.,Ningxia University | Zheng F.,Ningxia University | Qiu Z.,Institute of Liupanshan Flowers | Yao Y.,Institute of Arid Meteorology
Agriculture, Ecosystems and Environment | Year: 2013

Our objective was to elucidate the effects of climate change on crop water use efficiency in the northwest semiarid area of China. Improving crop water use efficiency can increase crop production levels and the efficient use of water resources under climate change conditions. This study investigated the effects of climate change on crop water use efficiency in the northwest semiarid region by statistically analyzing crop yields, soil moisture, rainfall and temperature data over the past 50 years. The results showed that, compared with 1960-1969, a temperature rise of 1.6°C and an annual rainfall reduction of 105.6mm occurred between 1990 and 2009 and the water use efficiency of wheat, potatoes and corn increased by 10.7, 4.5 and 12.2kghm-2mm-1, respectively. Due to climate warming and to a fall in rainfall over the past 50 years, water use efficiency by wheat (Triticum aestivum), potatoes (Solanum tuberosum) and corn (Zea mays) have significantly increased, which shows that climatic change can improve water use efficiency. © 2013 Elsevier B.V.

Wang J.,Institute of Arid Meteorology | Chen F.,Lanzhou University | Jin L.,Lanzhou University | Bai H.,Institute of Arid Meteorology
Climate Research | Year: 2010

Stretching from the Caspian Sea in the west to the western part of northeast China in the east, arid central Asia is a transition belt between high latitude and low latitude areas. The arid climate of this geographic region has environmental effects far beyond its borders. In this study, the dry/wet trend in arid central Asia was examined over a temporal scale of 100 yr. Dry/wet change in an area is affected not only by precipitation, but also by temperature, because of its effect on potential evaporation. To more accurately describe the dry/wet trend, a drought index (DRI) was developed and calculated from gridded monthly air temperature and precipitation data from the Climate Research Unit, University of East Anglia, UK. Analysis of the DRI shows a general warm and dry trend for the region for the whole period between 1901 and 2002. A dry trend is seen in particular in the western part of Uzbekistan and Turkmenistan, central Kazakhstan, southern Xinjiang in China, and central Mongolia for the same period, while in northern Xinjiang, China, there was a weak wet trend. Over the past 100 yr, central Asia has experienced 6 wet-dry cycles: 1901-1910, 1911-1925, 1926-1935, 1936-1950, 1951-1960, and 1961-2002. The period and trend of the DRI are different from those of precipitation for the last 100 yr. The DRI can be used as an indicator of dry/wet change in arid central Asia because it reflects the concurrent effects of temperature and precipitation. © Inter-Research 2010.

Wang J.,Institute of Arid Meteorology
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2010

The rainy and rainless years, and the higher and lower temperature years in arid central Asia were divided by using the gridded monthly air temperature and precipitation data from the Climate Research Unit (CRU) and the Tyndall Center, University of East Anglia, UK. And the mechanisms of temperature and precipitation change in these typical years were analyzed by using the NCEP/NCAR data from the National Centers for Environmental Prediction and the National Center for Atmospheric Research of USA. The results show that in the rainy years, the ascending motion areas are located in the west part of arid central Asia in winter and in the east part in summer. No matter in the rainy or rainless years, the sinking motion areas are located in the east part of arid central Asia in winter and in the west part in summer. For precipitation, in winter, the dynamical structure of rainy years presents decreasing of the Ural pressure ridge and East Asian trough in association with the deepening of East European trough. In opposite, the Ural pressure ridge and East Asian trough has a stiffness condition and the meridional airflow strengthening in the rainless years. In summer, the dynamical structure of rainy years presents the strengthening of East European high pressure ridge and the western Pacific subtropical high ridge in association with the western-spread of subtropical ridge. For temperature, in winter, the west part of arid central Asia is affected by south-west warm airflow and the east part is affected by north-west airflow in higher temperature years. However, the whole arid central Asia is controlled by north-west airflow in lower temperature years. In summer, the intensity and location of the west Pacific subtropical high pressure play an important role in determining the higher or lower temperature years. It should be higher temperature years when the subtropical high pressure strengthens and western-spreads. It should be lower temperature years when the subtropical high pressure decreases and withdraws eastward. © 2010 IEEE.

Zhang H.,CSIRO | Zhang L.,Institute of Arid Meteorology | Pak B.,CSIRO
Theoretical and Applied Climatology | Year: 2011

In this study, we analyze results from 47-year (1954-2000) offline simulations using an Australian land-surface model CSIRO Atmosphere Biosphere Land Exchange. We focus on exploring its surface mean climatology, interannual and decadal variations in Australia and Amazonia basin in South America which are distinguished by dry and wet climates respectively. Its skill is assessed by using observational datasets and four model products from the Global Land-surface Data Assimilation System. Surface evaporation and runoff climatologies are satisfactorily simulated, including surface energy and water partitions in dry and wet climates. In the Australian continent dominated by dry climate, slowly varying soil moisture processes are simulated in the southeast during austral winter. The model is skilful in reproducing the nonlinear relationship between rainfall and runoff variations in the southwestern part of the Australia. It shows that the significant downward trend of river inflow in the region is associated with enhanced surface evaporation which is caused by increased surface radiation and wind speed. In its carbon-cycle modeling, the model simulates an upward trend of NPP by about 0. 69%/year over the Amazonia forest region in the 47-year period. By comparing two sets of the model results with/without CO2 variations, it shows that 35% of such increases are caused by changes in climatic conditions, while 65% is due to the increase in atmospheric CO2 concentration. Given the close linkage between climate, water and vegetation (carbon cycle), this work promotes an integrated modeling and evaluation approach for better representation of land-surface processes in Earth system studies. © 2010 Springer-Verlag.

Wang S.,Lanzhou University | Wang S.,Institute of Arid Meteorology | Zhang Q.,Lanzhou University | Zhang Q.,Institute of Arid Meteorology
Wuli Xuebao/Acta Physica Sinica | Year: 2011

Based on the data measured in 2009 in the DingXi, a typical semi-arid region in loess plateau, the temporal variation of condensed water and the influence factors are investigated. Meanwhile, the measurements of condensed water, made by weighing approach and eddy-correlation approach separately, are compared in this work. The results show that in the semi-arid regions in Loess Plateau, the daily maximum amount of condensation can reach 0.33 mm, the daily minimum recorded is 0.09 mm, and the average daily amount is 0.23 mm. No obvious correlations is found between the amount of condensation and wind velocity, relative humidity, temperature, or land-air temperature difference. In the process of dew formation, the relative humidity which supplies the water vapor for condensing is an internal factor. The temperature which is motive power for condensing process is a key factor. The wind speed has an important effect and is an uncertain factor, which promotes but also can restrain the dew formation. It is also found that the following conditions favor the condensation process: wind speed of 0.5-2 m/s, relative humidity >80% and land-air temperature difference <±2°C. © Chinese Physical Society.

Yang F.,Institute of Arid Meteorology | Zhang Q.,Institute of Arid Meteorology | Wang R.,Institute of Arid Meteorology | Zhou J.,Lanzhou University
PLoS ONE | Year: 2014

Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m-2). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day-1. Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (p<0.001). The farmland Kc values showed the obvious seasonal fluctuation, with the average of 0.46. The correlation analysis between daily Kc and its major environmental factors indicated that wind speed (Ws), relative humidity (RH), soil water content (SWC), and atmospheric vapor pressure deficit (VPD) were the major environmental regulations of daily Kc. The regression analysis results showed that Kc exponentially decreased with Ws increase, an exponentially increased with RH, SWC increase, and a linearly decreased with VPD increase. An experiential Kc model for the semi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values. © 2014 Yang et al.

Qian C.,CAS Institute of Atmospheric Physics | Qian C.,Institute of Arid Meteorology | Zhou T.,CAS Institute of Atmospheric Physics
Journal of Climate | Year: 2014

North China has undergone a severe drying trend since the 1950s, but whether this trend is natural variability or anthropogenic change remains unknown due to the short data length. This study extends the analysis of dry-wet changes in north China to 1900-2010 on the basis of self-calibrated Palmer drought severity index (PDSI) data. The ensemble empirical mode decomposition method is used to detect multidecadal variability. A transition from significant wetting to significant drying is detected around 1959/60. Approximately 70% of the drying trend during 1960-90 originates from 50-70-yr multidecadal variability related to Pacific decadal oscillation (PDO) phase changes. The PDSI in north China is significantly negatively correlated with thePDO index, particularly at the 50-70-yr time scale, and is also stable during 1900-2010. Composite differences between two positive PDO phases (1922-45 and 1977-2002) and one negative PDO phase (1946-76) for summer exhibit an anomalous Pacific-Japan/East Asian-Pacific patternlike teleconnection, which may develop locally in response to the PDO-associated warm sea surface temperature anomalies in the tropical Indo-Pacific Ocean and meridionally extends from the tropical western Pacific to north China along the East Asian coast. North China is dominated by an anomalous high pressure system at mid-low levels and an anticyclone at 850 hPa, which are favorable for dry conditions. In addition, a weakened land-sea thermal contrast in East Asia from a negative to a positive PDO phase also plays a role in the dry conditions in north China by weakening the East Asian summer monsoon. © 2014 American Meteorological Society.

Zhang C.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Zhang C.,Institute of Arid Meteorology | Zhang H.,Center for Australian Weather and Climate Research | Zhang H.,Institute of Arid Meteorology
Theoretical and Applied Climatology | Year: 2010

This study explores potential impacts of the East Asian winter monsoon (EAWM) on summer climate variability and predictability in the Australia-Asian region through Australia-Asia (A-A) monsoon interactions. Observational analysis is conducted for the period of 1959 to 2001 using ERA-40 wind reanalysis and Climate Research Unit rainfall and surface temperature monthly datasets. Statistically significant correlations are established between the Australian summer monsoon and its rainfall variations with cross-equatorial flows penetrating from South China Sea region and northerly flow in the EAWM. The underlying mechanism for such connections is the response of the position and intensity of Hardley circulation to strong/weak EAWM. A strong EAWM is associated with an enhanced cross-equatorial flow crossing the maritime continent and a strengthened Australia summer monsoon westerlies which affect rainfall and temperature variations in northern and eastern part of the Australian continent. Furthermore, partial correlation analysis, which largely excludes El Niño-Southern Oscillation (ENSO) effects, suggests that these connections are the inherent features in the monsoon system. This is further supported by analyzing a global model experiment using persistent sea surface temperatures (SSTs) which, without any SST interannual variations, shows similar patterns as in the observational analysis. Furthermore, such interaction could potentially affect climate predictability in the region, as shown by some statistically significant lag correlations at monthly time scale. Such results are attributed to the impacts of EAWM on regional SST variations and its linkage to surface conditions in the Eurasian continent. Finally, such impacts under global warmed climate are discussed by analyzing ten IPCC AR4 models and results suggest they still exist in the warmed climate even though the EAWM tends to be weaker. © 2010 Springer-Verlag.

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