Zhaofei Liu

Comparison of surface variables from ERA and NCEP reanalysis with station data over eastern China

This study compared precipitation, mean air temperature (MAT) and mean sea level pressure (MSLP) from two widely used reanalysis datasets (ERA-40 and NCEP) with those from observed stations across eastern China. The evaluation was based on a comparison of both temporal and spatial variability and included several assessment criteria such as the mean values, normalized root mean square error, Mann–Kendall test, empirical orthogonal functions (EOFs) and probability density functions. The results showed that both the ERA-40 and NCEP datasets could capture temporal and spatial variability of the observed precipitation, MAT and MSLP over eastern China. The results showed that the two reanalysis datasets performed better for MAT and MSLP than for precipitation. Overall, the two reanalysis datasets revealed reasonable agreement with observations according to the evaluation. ERA-40 was better at capturing the temporal and spatial distributions for these three variables than NCEP, especially for MAT and MSLP. NCEP tended to overestimate the annual precipitation for both mean and extreme values, while ERA-40 tended to underestimate it, particularly for extreme values. The two reanalysis datasets performed better in the east and northeast regions of the study area than in other regions for capturing the temporal variability of MAT and MSLP. ERA-40 was poor at capturing the temporal variability of precipitation in northeastern China. According to the trend analysis, the two reanalysis datasets showed lower trends for MAT and precipitation and higher trends for MSLP. Both ERA-40 and NCEP had larger explained variances for the first two EOFs than the observed precipitation. This implies that both reanalysis datasets tend to simulate a more uniform spatial distribution for precipitation in the study area.

Assessing Crop Water Demand and Deficit for the Growth of Spring Highland Barley in Tibet, China

The aim of this study was to assess the crop water demand and deficit of spring highland barley and discuss suitable irrigation systems for different regions in Tibet, China. Long-term trends in reference crop evapotranspiration and crop water demand were analyzed in different regions, together with crop water demand and deficit of spring highland barley under different precipitation frequencies. Results showed that precipitation trends during growth stages did not benefit the growth of spring highland barley. The crop coefficient of spring highland barley in Tibet was 0.87 and crop water demand was 389.0 mm. In general, a water deficit was found in Tibet, because precipitation was lower than water consumption of spring highland barley. The most severe water deficit were in the jointing to heading stage and the heading to wax ripeness stage, which are the most important growth stages for spring highland barley; water deficit in these two stages would be harmful to the yield. Water deficit showed different characteristics in different regions. In conclusion, irrigation systems may be more successful if based on an analysis of water deficit within different growth stages and in different regions.

Glacier retreat and its effect on stream flow in the source region of the Yangtze River

There is growing concern over the effects of climate change on glacier melt and hydrology. In this article, we used two natural small-scale basins, Tuotuo River and Buqu River in the source region of the Yangtze River, China, to show the impacts of glacier melt on stream flow. Changes in the extent of glaciers and ice volume in 1970, 1992 and 2009 are evaluated using remote sensing images. Changes to the glacier surface area over the same time interval are estimated through the delineation of glacier outlines and positions using Landsat TM/ETM+ imagery. By 2009, the glacier surface area had decreased by 20.83% and 34.81% of the 1970 values in Tuotuo River and Baqu River basins respectively. The total meltwater supply in each basin is estimated to be 2.56×109 m3/yr and 1.24×109 m3/yr respectively. Mass balance calculations show that glaciers in the study area suffered a constant mass loss of snow and ice, accumulatively approximately −24 m over the past 40 years. The annual and summer stream flow tended to increase in Tuotuo River basin from 1970 to 2009 while a negative trend of change was shown in Buqu River basin during 1970–1986. Glaciers became shorter, narrower and thinner under the effect of atmospheric warming. Streamflow increase has been recorded at Tuotuo River station in response to increased glacier and permafrost melt. However, streamflow decrease has been recorded at Yanshiping station on Buqu River, where glacier melt has lagged behind atmospheric warming. These results show a close but variable linkage among climate change, glacier melting and water resources in the source region of the Yangtze River.

Spatial-temporal patterns of major ion chemistry and its controlling factors in the Manasarovar Basin, Tibet

The Manasarovar Basin in southern Tibet, which is considered a holy land in Buddhism, has drawn international academic attention because of its unique geographical environment. In this study, based on actual measurements of major ion concentrations in 43 water samples collected during the years 2005 and 2012, we analyzed systemically the spatial-temporal patterns of water chemistry and its controlling factors in the lake and inflowing rivers. The results reveal that the water in the Manasarovar Basin is slightly alkaline, with a pH ranging between 7.4–7.9. The amounts of total dissolved solids (TDS) in lake and river waters are approximately 325.4 and 88.7 mg/l, respectively, lower than that in most of the surface waters in the Tibetan Plateau. Because of the long-term effect of evaporative crystallization, in the lake, Na+ and HCO3− have the highest concentrations, accounting for 46.8% and 86.8% of the total cation and anion content. However, in the inflowing rivers, the dominant ions are Ca2+ and HCO3−, accounting for 59.6% and 75.4% of the total cation and anion content. The water exchange is insufficient for such a large lake, resulting in a remarkable spatial variation of ion composition. There are several large inflowing rivers on the north side of the lake, in which the ion concentrations are significantly higher than that on the other side of the lake, with a TDS of 468.9 and 254.9 mg/l, respectively. Under the influence of complicated surroundings, the spatial variations in water chemistry are even more significant in the rivers, with upstreams exhibiting a higher ionic content. The molar ratio between (Ca2++Mg2+) and (Na++K+) is much higher than 1.0, revealing that the main source of ions in the waters is carbonate weathering. Although natural processes, such as rock weathering, are the major factors controlling main ion chemistry in the basin, in the future we need to pay more attention to the anthropogenic influence.

Changes in Climate Extremes and Catastrophic Events in the Mongolian Plateau from 1951 to 2012

AbstractThe spatiotemporal changes in 21 indices of extreme temperature and precipitation for the Mongolian Plateau from 1951 to 2012 were investigated on the basis of daily temperature and precipitation data from 70 meteorological stations. Changes in catastrophic events, such as droughts, floods, and snowstorms, were also investigated for the same period. The correlations between catastrophic events and the extreme indices were examined. The results show that the Mongolian Plateau experienced an asymmetric warming trend. Both the cold extremes and warm extremes showed greater warming at night than in the daytime. The spatial changes in significant trends showed a good homogeneity and consistency in Inner Mongolia. Changes in the precipitation extremes were not as obvious as those in the temperature extremes. The spatial distributions in changes of precipitation extremes were complex. A decreasing trend was shown for total precipitation from west to east as based on the spatial distribution of decadal tr...

Comparison of surface water chemistry and weathering effects of two lake basins in the Changtang Nature Reserve, China.

The geochemistry of natural waters in the Changtang Nature Reserve, northern Tibet, can help us understand the geology of catchments, and provide additional insight in surface processes that influence water chemistry such as rock weathering on the Qinghai-Tibet Plateau. However, severe natural conditions are responsible for a lack of scientific data for this area. This study represents the first investigation of the chemical composition of surface waters and weathering effects in two lake basins in the reserve (Lake Dogaicoring Qiangco and Lake Longwei Co). The results indicate that total dissolved solids (TDS) in the two lakes are significantly higher than in other gauged lakes on the Qinghai-Tibet Plateau, reaching 20-40g/L, and that TDS of the tectonic lake (Lake Dogaicoring Qiangco) is significantly higher than that of the barrier lake (Lake Longwei Co). Na(+) and Cl(-) are the dominant ions in the lake waters as well as in the glacier-fed lake inflows, with chemical compositions mainly affected by halite weathering. In contrast, ion contents of inflowing rivers fed by nearby runoff are lower and concentrations of dominant ions are not significant. Evaporite, silicate, and carbonate weathering has relatively equal effects on these rivers. Due to their limited scope, small streams near the lakes are less affected by carbonate than by silicate weathering.

Temporal and Spatial Variations of Precipitation δ18O and Controlling Factors on the Pearl River Basin and Adjacent Regions

Based on the precipitation  δ18O values from the datasets of the Global Network of Isotopes in Precipitation (GNIP), the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis data, and previous researches, we explored the temporal and spatial variations of precipitation  δ18O in a typical monsoon climate zone, the Pearl River basin (PRB), and adjacent regions. The results showed that the temporal variations of precipitation  δ18O for stations should be correlated with water vapor sources, the distance of water vapor transport, the changes in location, and intensity of the intertropical convergence zone (ITCZ) rather than “amount effect.” Meanwhile, local meteorological and geographical factors showed close correlations with mean weighted precipitation  δ18O values, suggesting that “altitude effect” and local meteorological conditions were significant for the spatial variations of precipitation  δ18O. Moreover, we established linear regression models for estimating the mean weighted precipitation  δ18O values, which could better estimate variations in precipitation  δ18O than the Bowen and Wilkinson model in the PRB and adjacent regions.

Area Errors Between Grid Imagery Boundaries and Vector Actual Boundaries Identifying Waterbodies from Remote Sensing Imagery

In identifying water bodies from remote sensing imagery, a mismatch between grid data boundary and vector boundary has always existed but was seldom studied. Therefore, area errors between grid imagery boundaries and vector real boundaries are the subject of this study. A solution based on the sub-pixel classification method was developed to analyse these errors. A case study from Lake Manasarowar in China showed that the area error proposed in this study is larger than that from different interpretation methods. It was concluded that uncertainties from mixed boundary pixels were greater than that from different methods for identifying lake area using the remote sensing imagery in the study area. Overall, area error analyses for grid imagery boundaries and vector real boundaries are necessary for identifying water bodies from remote sensing imagery. It is also useful for the interpretation of other continuous bodies, such as glaciers.

Analysis on the Spatio-temporal Variability of Rainy Season Precipitation in Henan Province

With the extensive application of geographic information systems and the deeply development of geography disciplines,the spatial and temporal structure and process analysis are receiving more attention.The analysis of spatio-temporal variability of precipitation is the basis for the understanding of formation and development of regional water resources.It not only reveals the change of time-series,but finds the spatial structure and changing pattern.Thus,it provides the basis for predicting the drought and waterlogging.Based on the rainy season precipitation data of the past 51 years in Henan Province,combined with a digital elevation model(DEM),using regression analysis,spatial autocorrelation,simulation of spatial interpolation,and cross-validation,we conducted an analysis of spatial and temporal variability of precipitation in Henan Province.The result reveals that:(1) the trend is clear,and the rainy season precipitation in Henan Province overall has shown an increasing trend and in recent years it is particularly evident;(2) The differences of monthly precipitation are obvious,the maximum value is in July,and the average reaches 178.3 mm.(3) The spatial variance exists.There is a clear pattern that the precipitation in the south and east are more than that of north and west in spatial.There is a strong clustering characteristic that in the south,Luoshan and Huangchuan counties as the center formed the rainfall abundant areas,while in the north,Hui County as the center formed the rainfall scarce areas.Lin,Luanchuan and Xixia counties as spatial outliers,are significantly higher than the adjacent regional precipitation.After the spatial autocorrelation analysis,the spatial and temporal anisotropy can be acquired.Therefore,according to the spatio-temporal analysis,we get the interpolation map with Cokriging method,and it tallies with the prior conclusion.