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The aims are to validate and assess the performances of MODIS gross primary production (MODIS-GPP) and evapotranspiration (MODIS-ET) products in China's different land cover types and their sensitivity to remote sensing input data. In this study, MODIS-GPP and -ET are evaluated using flux derived/measured data from eight sites of ChinaFLUX. Results show that MODIS-GPP generally underestimates GPP (R2 is 0.58, bias is -6.7 gC/m2/8-day and RMSE is 19.4 gC/m2/8-day) at all sites and MODIS-ET overestimates ET (R2 is 0.36, bias is 6 mm/8-day and RMSE is 11 mm/8-day) when comparing with derived GPP and measured ET, respectively. For evergreen forests, MODIS-GPP gives a poor performance with R2 varying from 0.03 to 0.44; in contrast, MODIS-ET provides more reliable results. In croplands, MODIS-GPP can explain 80% of GPP variance, but it overestimates flux derived GPP in non-growing season and underestimates flux derived GPP in growing season; similar overestimations also presented in MODIS-ET. For grasslands and mixed forests, MODIS-GPP and -ET perform good estimating accuracy. By designing four experimental groups and taking GPP simulation as an example, we suggest that the maximum light use efficiency of croplands should be optimized, and the differences of meteorological data have little impact on GPP estimation, whereas remote sensing leaf area index/fraction of photo-synthetically active radiation (LAI/FPAR) can greatly affect GPP/ET estimations for all land cover types. Thus, accurate remote sensing parameters are important for achieving reliable estimations. [ABSTRACT FROM AUTHOR]

Rapid urbanization has occurred in northwestern China, threatening the sustainability of its fragile dryland ecosystems. A lack of precise urban land-cover information has limited our understanding on the urbanization in the dryland. Here, we examined urban land-cover changes from 2000 to 2014 in 21 major cities that comprise over 50% of the developed land in arid China, using Landsat Enhanced Thematic Mapper Plus and Operational Land Imager data, and a hybrid classification method. The 15-m resolution urban land-cover products (including impervious surfaces, vegetation, bare soil, and water bodies) had an overall accuracy of 90.37%. Based on these new land use products, we found the urbanization in arid China was characterized by the dramatic expansion of impervious surface (+13.23%) and reduction of bare soil (-13.41%), while the proportions of vegetation (+0.27%) and water (-0.10%) remained stable. The observed dynamic equilibrium of vegetated ratio implies an increasing harmonization of urbanization and greening, which was particularly important for the sustainability of fragile urban ecosystems in arid regions. From an economic perspective, gross domestic product and population were significantly correlated with impervious surfaces, and oasis cities displayed a stronger ability to attract new residents than desert cities. [ABSTRACT FROM AUTHOR]

Advances in the timing of spring green-up date are a typical response of vegetation global change. Long-term observations of plant phenology have been used to track vegetation response to climate change. Normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) have been the most commonly used indicators in reconstructing spring green-up dates from remote sensing over the past several decades. The Moderate Resolution Imaging Spectroradiometer (MODIS) based phenology time series from NDVI and EVI with an enhanced TIMESAT algorithm are the two operational phenology products developed recently with sun-sensor geometry corrected reflectance. However, a comprehensive intercomparison and evaluation of these two spring green-up datasets using intensive ground observations have not been conducted, limiting their applications in regional interpretation of land surface phenology. Therefore, we used 455 ground observations from USA National Phenology Network (NPN) and 106 observations from 21 AmeriFlux sites to assess and validate the spring green-up dates for United States for 2000-2013. Our results indicate that the spring green-up dates from NDVI and EVI showed a good agreement in eastern United States, while substantial differences (70 days) were found in western and southern areas. Ground observations generally had a significant correlation (p < 0.01) with the two MODIS spring green-up dates, especially for deciduous broadleaf forests with root mean square error (RMSE) of 12 days and 16 days when compared with USA-NPN and AmeriFlux observations, respectively. Spring green-up dates from EVI overall showed a better relationship and a lower RMSE in reference to both USA-NPN and AmeriFlux observations than NDVI-based spring green-up dates. Our results highlight the importance of a rigorous validation of remote sensing products to better understand their limitations in operational applications. [ABSTRACT FROM AUTHOR]

China's Loess Plateau (LP) is one of the most typical regions with serious soil erosion. Its ecological restoration, economic development, and social progress are directly related to realizing China's national sustainable development goals (SDGs). With intensive field investigations, comprehensive analyses of statistical data, remote sensing data, and local monitoring data, this current research explored the achievements in local ecological restoration and economic development, discussed the main problems faced by the LP, and assessed the sustainable development status of the LP. Moreover, drawing from a 3C system approach (classification–coordination–collaboration), this research proposed the sustainable development strategies for more sustainable LP. We found that the LP's ecological restoration and economic development made remarkable achievements since 2000. However, the environment was still fragile and regional development was still lagging behind. In realizing SDGs, further improvements on clean water and sanitation, decent work and economic growth, industry, innovation and infrastructure, reduced inequalities, and climate action are needed. Coordinated and collaborated efforts are expected from multiple hierarchical levels including household, watershed, region, and nation in developing LP. Specifically, human-environment interactions should be highlighted at the household level, upstream-downstream interactions that are catering to the particular characteristics of the LP is encouraged at the watershed level, and regional and urban-rural interactions shall play an increasingly important role at the regional level. While at the national level, the central government should carry out a systematic overarching design. To better realize the goal of more sustainable LP, this research calls for (1) forming an actor-network consists of multi stakeholders, including the central government, local government, watershed, families, ecosystem and environment, enterprises, NGOs, and scientists, and (2) paying attention to ecosystem management, ecological restoration, industrial structure optimization, ecological agriculture, rural infrastructure, and ecological civilization construction in the future development. Unlabelled Image • The Loess Plateau has made remarkable achievements in ecological restoration and economic development. • Main problems faced by the Loess Plateau are discussed. • We assessed the status of sustainable development in the Loess Plateau. • Strategy for More Sustainable Loess Plateau has been constructed based on Classification–Coordination–Collaboration approach. • Key tasks in the field of environment, economy and society for SDGs were identified. [ABSTRACT FROM AUTHOR]