Assessing MODIS Land Cover Products over China with Probability of Interannual Change

Accurate and up-to-date land cover data are important for climate-change modeling. Quality assessment is becoming critical, as many satellite-based land cover products of differing scales have been released to meet the needs of scientific studies. In this study, the authors assessed the Moderate Resolution Imaging Spectroradiometer(MODIS) land cover products by analyzing the probability of interannual change from 2001 to 2012. The authors found that, cumulatively, 43.0% of MODIS land cover had changed over China from 2001 to 2012 at least once. Of this percentage, 12.1% was considered unreasonable change, 6.1% was considered reasonable change, and areas of confusion accounted for about 24.8%, giving rise to great uncertainty in the products. MODIS Collection 51 products clearly have less uncertainty than the Collection 5 products. Areas of reasonable change occurred in transition zones of ecological, biophysical, and climate gradients, while areas of unreasonable change appeared in heterogeneous landscapes. The misclassifications at three spatial scales of horizontal grids used in regional climate models occurred largely in the heterogeneous landscapes, and the areal percentage of misclassification decreased with larger horizontal grid spacing. In addition, the misclassifications in MODIS products often occurred among specific classes, which are geographically, ecologically, and spectrally similar, with low discriminative spectral-temporal signals. The effect of classification uncertainty should be made known, and further improvements are still needed for application in regional climate models. The authors' findings have important implications for better understanding the uncertainties of MODIS land cover products, and for improving the land surface parameterization for regional climate models.

Interannual Changes of Land Surface Radiation Components in Loess Plateau and Their Responses to Climate Change

In this paper,land surface observation data at semi-arid climate and environmental observation station（ SACOL station） of Lanzhou University during 2006- 2012 and the data of Yuzhong meteorological station were used to analyze the responses of land surface radiation budget components to climate fluctuation,study the interannual variability of surface albedo,and discuss the feedback of various land surface process parameters on the interannual fluctuations of temperature and precipitation in Loess Plateau. According to the type of precipitation in Loess Plateau,the year was divided into winter and summer in order to get more significant interannual variability and correlation. The results showed that the trends of temperature and precipitation during 2006- 2012 were consistent with the warming and drying total trend in recent years in Loess Plateau. Shallow surface soil moisture and temperature showed a good response to temperature and precipitation,and the annual variation of summer half year had greater impact on the trend in the whole year. Incident solar radiation increase was major reason for climate warming in the Loess Plateau region.The combined effect of climatic factors was the reason for the change of surface albedo. Through the distinguish inquiry by winter and summer data,it was obtained that most correlations between summer radiation components and climatic factors have been improved,and partial correlations between winter radiation components and climatic factors have been increased.

Interannual Variability of the Normalized Difference Vegetation Index on the Tibetan Plateau and Its Relationship with Climate Change

The Qinghai-Xizang Plateau, or Tibetan Plateau, is a sensitive region for climate change, where the manifestation of global warming is particularly noticeable. The wide climate variability in this region significantly affects the local land ecosystem and could consequently lead to notable vegetation changes. In this paper, the interannual variations of the plateau vegetation are investigated using a 21-year normalized difference vegetation index （NDVI） dataset to quantify the consequences of climate warming for the regional ecosystem and its interactions. The results show that vegetation coverage is best in the eastern and southern plateau regions and deteriorates toward the west and north. On the whole, vegetation activity demonstrates a gradual enhancement in an oscillatory manner during 1982-2002. The temporal variation also exhibits striking regional differences： an increasing trend is most apparent in the west, south, north and southeast, whereas a decreasing trend is present along the southern plateau boundary and in the central-east region. Covariance analysis between the NDVI and surface temperature/precipitation suggests that vegetation change is closely related to climate change. However, the controlling physical processes vary geographically. In the west and east, vegetation variability is found to be driven predominantly by temperature, with the impact of precipitation being of secondary importance. In the central plateau, however, temperature and precipitation factors are equally important in modulating the interannual vegetation variability.

Interannual Variation Characteristics of the Atmospheric Dust Deposition on Typical Region of Chaihe Basin

[Objective]The aim was to study the interannual changes of atmospheric dust deposition and quantity of combustible dust-fall in Chaihe basin.[Method]Taking Chaihe Basin in south Dianchi as study area,the atmospheric dust deposition and combustible substances in the residential,chemical area,sand production area and watershed in Chaihe basin were measured.The pollution and interannual changes of atmospheric dust in Chaihe basin were discussed.[Result]In the residential,chemical area,sand production area and watershed,the amount of sand was the highest in sand production area and lowest in the watershed.While the dust amount in the chemical area and watershed areas were lower than sand production area and higher than watershed area.In the four chosen areas,the highest value of dust appeared in autumn and the lowest value appeared in precipitation season.Sand in other months changed and the change scale was large,which indicated that the meteorological condition had large influences on dust.Relevance analysis indicated that the dust in sand production area showed positive relevance to flammable amount of dust.Dust and flammable amount had positive relevance.[Conclusion]The study provided theoretical basis for the atmospheric pollution situation in Chaihe Basin.

Temporal and spatial variations in extreme temperatures in the Qilian Mountains-Hexi Corridor over the period 1960-2013

Based on daily maximum and minimum temperatures at 18 meteorological stations in the Qilian Mountains and Hexi Corridor between 1960 and 2013,temporal and spatial variations in extreme temperatures were analysed using linear trends,tenpoint moving averages and the Mann-Kendall test.The results are as follows:The trends in the majority of the extreme temperature indices were statistically significant,and the changes in the extreme temperatures were more obvious than the changes in the extreme values.The trends were different for each season,and the changes in rates and intensities in summer and autumn were larger than those in spring and winter.Unlike the cold indices,the magnitudes and trends of the changes in the warm indices were larger and more significant in the Hexi Corridor than in the Qilian Mountains.Abrupt changes were detected in the majority of the extreme temperature indices,and the extreme cold indices usually occurred earlier than the changes in the extreme warm indices.The abrupt changes in the extreme temperatures in winter were the earliest among the four seasons,indicating that these temperature changes were the most sensitive to global climate change.The timing of the abrupt changes in certain indices was consistent throughout the study area,but the changes in the cold indices in the Hexi Corridor occurred approximately four years before those in the Qilian Mountains.Similarly,the changes in the warm indices in the western Hexi Corridor preceded those of the other regions.

A climatological northern boundary index for the East Asian summer monsoon and its interannual variability

A long-term perspective on the spatial variation of the northern boundary of the East Asian summer monsoon(EASM) and the related physical mechanisms is important for understanding past climate change in Asia and for predicting future changes. However, most of the meteorological definitions of the EASM northern boundary do not correspond well to the actual geographical environment, which is problematic for paleoclimatic research. Here, we use monthly CMAP and GPCP precipitation data to define a new EASM northern boundary index by using the concept of the global monsoon, which is readily applicable to paleoclimatic research. The results show that the distribution of the 2 mm day^(-1) precipitation isoline(i.e., 300 mm precipitation)has a good relationship with the spatial distribution of modern land cover types, the transitional climate zone and the potential natural vegetation types, in China. The locations of the precipitation isolines also correspond well to the locations of major shifts in wind direction. These results suggest that the 2 mm day^(-1) isoline has a clear physical significance since the climatic, ecological,and geographical boundary can be used as the northern boundary index of the EASM(which we call the climatological northern boundary index). The index depicts the northeast-southwest orientation of the climatological(1981-2010) EASM northern boundary, along the eastern part of the Qilian Mountains-southern foothills of the Helan Mountains-Daqing Mountains-western margin of the Greater Khingan Range, from west to east across Northwest and Northeast China. The interannual change of the EASM northern boundary from 1980 to 2015 covers the central part of Gansu, the northern part of Ningxia, the eastern part of Inner Mongolia and the northeastern region in China. It can extend northward to the border between China and Mongolia and retreat southward to Shangdong-central Henan. There is a 200-700 km fluctuation range of the interannual EASM northern boundaries around the locations of the climatological northern boundary. In addition, the spatial variation of the interannual EASM northern boundaries gradually increases from west to east, whereas the trend of north-south fluctuations maintains a roughly consistent location in different regions.