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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.

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.

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.

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.

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