Urban Growth and Rural Transition in China Based on DMSP/OLS Nighttime Light Data

Nighttime light (NTL) images provide uniform, consistent, and valuable data sources. Based on four reference regions, the NTL imagery of China was fully intercalibrated during the period 1992–2012. Using lit areas and the intensity of NTL imagery, this study synthetically analyzed the urbanization process and rural transition in China. The results showed that, over the whole country, the pixel numbers of urban areas increased by 173% from 1992 to 2012. During the 2000s, urban areas expanded much more quickly than during the 1990s. Urban growth varied greatly across the four regions, which could be pictured using the flying-geese paradigm. In the 1990s, East China experienced the most rapid rate of growth, while a decade later Middle China had the highest growth rate. NTL imagery can also be used to describe changes in rural human activities if the imagery is corrected using completely dark rural pixels. In China, because of the massive rural-urban migration, some marginal regions experienced a decrease in nighttime light intensity (NTLI) and rural areas went through a period of transition

The Transition of Farmland Production Functions in Metropolitan Areas in China

In metropolitan areas of China, farmland functions have undergone tremendous changes due to rapid urbanization and rising income per capita in the past three decades. This study examines tempo-spatial changes in the farmland functions, using a case study of the Beijing metropolitan area. The results indicate that: (1) during the past three decades, agricultural production experienced two transitions, in the years 1992 and 2003; (2) In terms of spatial differences, farmland functions of food production in Near Suburb significantly weakened. Middle Suburb produced the largest share of vegetables, while Far Suburb had the highest number of recreational farms. This case study may provide insights for large cities in China or other developing countries

Use of an inside buffer method to extract the extent of urban areas from DMSP/OLS nighttime light data in North China

<p>Defense Meteorological Satellite Program (DMSP)/Operational Linescan System (OLS) nighttime imagery provides a valuable data source for mapping urban areas. However, the spatial extents of large cities are often overestimated because of the effect of over-glow from nighttime light if a fixed thresholding technique is used. In the work reported here, an inside buffer method was developed to solve this issue. The method is based on the fact that the area overestimated is proportional to the extent of the lit area if a fixed threshold is used to extract urban areas in a region/county. Using this method, the extents of urban areas in North China were extracted and validated by interpretations from Landsat Thematic Mapper images. The results showed that the lit areas had a significant linear relationship with the urban areas for 120 representative cities in North China in 2000, with an <i>R</i>² value of over 0.95. This demonstrates that the inside buffer method can be used to extract urban areas. The validation results showed that the inside buffer model developed in 2000 can be directly used to extract the extent of urban areas using more recent nighttime light imagery. This is of great value for the timely updating of urban area databases in large regions or countries.</p

Different Irrigation Water Requirements of Seed Corn and Field Corn in the Heihe River Basin

The Heihe River is the second largest river in arid areas of China, and the irrigation water of oasis agriculture in its middle reaches accounts for almost 80% of the water resources in the whole watershed. Corn is the most important crop in the middle reaches of the Heihe River, and its water consumption is about 50% of the total agriculture water consumption of the middle reaches. Therefore, in order to effectively use the water resources in the watershed, it is crucial to improve the efficiency of corn irrigation. In this paper, using the Ganzhou District in the middle reaches of the Heihe River as the study region, we carried out a field survey to obtain characteristics of seed and field corn. Based on our results, we conducted parameter calibration using the CROPWAT model and calculated the irrigation water requirements (IWR) of these two corn types. The irrigation water requirements of seed and field corn in the growing seasons were 470.1 and 488.5 mm, respectively. However, we observed big differences in the water consumption sequences of these two corn types. Prior to mid-July, evapotranspiration and IWR of seed corn were 14.3% and 20.1% higher, respectively, than those of field corn. In September, IWR of the two corn types started to decrease, with a value of 82.3 mm for seed corn, which was 32.1% lower than the IWR of field corn (108.7 mm) during the same period. However, there were no significant differences in the irrigation time and single irrigation amount for seed and field corn in the study area. Since corn is widely cultivated in the Zhangye Region, there is a considerable water-saving potential in agriculture if the irrigation water consumption can be adjusted according to the IWR of the two corn types

Spatial and Temporal Variations of Forest Cover in Developing Countries

An understanding of changes in forest cover and the drivers of forest transition (FT) contributes to the sustainable management of global forests. In this paper, we used the latest global land cover data published by the European Space Agency (ESA) to investigate spatiotemporal variation characteristics of forest cover in developing countries from 1992 to 2015, and then analyzed causal factors of this variation using a binary logistic regression model. Existing studies on FT are mostly based on data from the Food and Agriculture Organization (FAO); this study improves our understanding of FT mechanisms through the use of a new dataset. The results indicate that the forest area in developing countries decreased from 21.8 to 21.3 million km2 from 1992&ndash;2015, and the rate of decline slowed after 2004. South America suffered the largest reduction in forest area (505,100 km2), whereas forest area in Africa increased slightly. By 2015, more than 80% of African countries had experienced FT, whereas only half of developing countries experienced forest expansion in South America. The variables affecting FT occurrence differed among continents. On the global scale, the remaining forest coverage and the proportion of forest exports negatively affected the likelihood of FT occurrence, whereas urbanization level had a positive effect