Chunyang He

A global map of urban extent from nightlights

Urbanization, a major driver of global change, profoundly impacts our physical and social world, for example, altering not just water and carbon cycling, biodiversity, and climate, but also demography, public health, and economy. Understanding these consequences for better scientific insights and effective decision-making unarguably requires accurate information on urban extent and its spatial distributions. We developed a method to map the urban extent from the defense meteorological satellite program/operational linescan system nighttime stable-light data at the global level and created a new global 1 km urban extent map for the year 2000. Our map shows that globally, urban is about 0.5% of total land area but ranges widely at the regional level, from 0.1% in Oceania to 2.3% in Europe. At the country level, urbanized land varies from about 0.01 to 10%, but is lower than 1% for most (70%) countries. Urbanization follows land mass distribution, as anticipated, with the highest concentration between 30° N and 45° N latitude and the largest longitudinal peak around 80° W. Based on a sensitivity analysis and comparison with other global urban area products, we found that our global product of urban areas provides a reliable estimate of global urban areas and offers the potential for producing a time-series of urban area maps for temporal dynamics analyses.

Spatiotemporal dynamics of electric power consumption in Chinese Mainland from 1995 to 2008 modeled using DMSP/OLS stable nighttime lights data

Electric power consumption (EPC) is one of the basic indices for evaluating electric power use. Obtaining timely and accurate data on the spatiotemporal dynamics of EPC is crucial for understanding and practical deployment of electric power resources. In this study, an EPC model was developed using stable nighttime lights time-series data from the Defense Meteorological Satellite Program Operational Linescan System (DMSP/OLS). The model was used to reconstruct the spatial patterns of EPC in Chinese Mainland at the county level from 1995 to 2008. In addition, the spatiotemporal dynamics of EPC were analyzed, and the following conclusions were drawn. (1) The EPC model reliably represented the spatiotemporal dynamics of EPC in Chinese Mainland with approximately 70% accuracy. (2) The EPC in most regions of Chinese Mainland was at low to moderate levels, with marked temporal and spatial variations; of high-level EPC, 58.26% was concentrated in eastern China. Six urban agglomerations (Beijing-Tianjin-Tangshan region, Shanghai-Nanjing-Hangzhou region, Pearl River Delta, Shandong Peninsula, middle-south of Liaoning Province, and Sichuan Basin) accounted for 10.69% of the total area of Chinese Mainland but consumed 39.23% of the electricity. (3) The EPC of most regions in Chinese Mainland increased from 1995 to 2008, and 64% of the mainland area showed a significant increase in EPC. Moderate increases in EPC were found in 61.62% of eastern China and 80.65% of central China from 1995 to 2008, whereas 75.69% of western China showed no significant increase in EPC. Meanwhile, 77.27%, 89.35%, and 66.72% of the Shanghai-Nanjing-Hangzhou region, Pearl River Delta, and Shandong Peninsula, respectively, showed high-speed increases in EPC. Moderate increases in EPC occurred in 71.12% and 72.13% of the Beijing-Tianjin-Tangshan region and middle-south of Liaoning Province, respectively, while no significant increase occurred in 56.34% of the Sichuan Basin.

Modeling the spatiotemporal dynamics of electric power consumption in Mainland China using saturation-corrected DMSP/OLS nighttime stable light data

Obtaining timely and accurate data on the spatiotemporal dynamics of electric power consumption (EPC) is crucial for the effective utilization of electric power in China. The Defense Meteorological Satellite Programs Operational Linescan System (DMSP/OLS) nighttime stable light (NSL) data have good potential for estimating EPC effectively at large scales. However, saturated lighted pixels contained within the NSL data limit the accuracy of EPC estimation. We developed a new method to correct the saturated lighted pixels, using the SPOT VEGETATION (SPOT/VGT) 10-day synthesis product (S10) normalized difference vegetation index (NDVI) data and then modeled the spatiotemporal dynamics of EPC in Mainland China from 2000 to 2008. The results demonstrated the reliability of our approach with an average R value of 0.93 (P<0.001) and an average relative error of −28.92%. EPC in Mainland China showed an average annual growth rate of 13.46% during the study period from 1198.23 billion kWh in 2000 to 3290.51 billion kWh in 2008. EPC in Mainland China also showed clear regional variation. Northern coastal China and eastern coastal China consumed 37.61% of the total EPC in Mainland China, with only 25.96% of the population and 6.11% of the area.

Are the drylands in northern China sustainable? A perspective from ecological footprint dynamics from 1990 to 2010.

The drylands in northern China (DNC), characterized by water scarcity, high climatic variability, and infertile soil, are crucial for Chinas sustainable development in the context of rapid urbanization. However, few studies have systematically investigated its sustainability. Our objective was to assess the sustainability of the DNC according to their ecological footprint (EF) dynamics from 1990 to 2010. We analyzed EF in the DNC at multiple scales ranging from the whole, to four dryland subtypes, to the drylands in each province. We found that the total EF in the DNC increased from 3.48 × 10(8) global hectares (gha) in 1990 to 1.26 × 10(9) gha in 2010, with a growth of 2.63 times, resulting in a more than 14 times increase of ecological deficit from 6.26 × 10(7) gha to 9.63 × 10(8)gha. In addition, the water withdrawal increased from 133.29 km(3) to 153.23 km(3) with a growth rate of 14.96%, while the Human Development Index grew from 0.62 to 0.79. We concluded that the DNC has already become unsustainable after the rapid increases of EF and water withdrawal from 1990 to 2010. We argue that effective management is needed to maintain and improve the environmental sustainability of the DNC.

Studying urban development and change in the contiguous United States using two scaled measures derived from nighttime lights data and population census

We investigated urban development trend in contiguous United States based on metropolitan areas (MAs), using two scaled measurements for 1990, 2000 and 2010. Linear population density (LPD) was used to compare the same MA over time. Population area growth index (PAGI) was adopted to compare different MAs at the same time. We found that (1) DMSP-OLS nighttime stable lights data are effective for delineating extent of developed areas; (2) both measurements show the growth of developed land have slowed from 1990 to 2010; (3) both measurements show clear regional pattern in urban development in contiguous United States.

The population in China’s earthquake-prone areas has increased by over 32 million along with rapid urbanization

Accurate assessments of the population exposed to seismic hazard are crucial in seismic risk mapping. Recent rapid urbanization in China has resulted in substantial changes in the size and structure of the population exposed to seismic hazard. Using the latest population census data and seismic maps, this work investigated spatiotemporal changes in the exposure of the population in the most seismically hazardous areas (MSHAs) in China from 1990 to 2010. In the context of rapid urbanization and massive rural-to-urban migration, nearly one-tenth of the Chinese population in 2010 lived in MSHAs. From 1990 to 2010, the MSHA population increased by 32.53 million at a significantly higher rate of change (33.6%) than the national average rate (17.7%). The elderly population in MSHAs increased by 81.4%, which is much higher than the groups national growth rate of 58.9%. Greater attention should be paid to the demographic changes in earthquake-prone areas in China.