Permafrost is a product of long-term thermal exchanges between the ground surface and atmosphere; thus, the ground surface thermal regime and freeze-thaw cycles highlight the complex thermal influences resulting from multi-interactions between the atmosphere and underlying surface characteristics and reflect the variation in the thermal regime of the near-surface shallow frozen soils. Based on the ground surface temperature observations from 51 sites in the Headwater Area of the Yellow River (HAYR), the ground surface freezing and thawing indexes were calculated, the freezing and thawing processes were analyzed, and their spatial differentiations were explored. The results showed that the mean annual ground surface temperature (MAGST) in the HAYR ranges from -3.06 to 1.31 °C, exhibiting extremely strong spatial differentiation, the differentiation of ground surface temperature is mainly affected by elevation, latitude, and NDVI (P < 0.001) on a regional scale, the MAGST decreases at a vertical lapse rate of about 0.7 ℃·(100 m)^-1. The larger value of NDVI represents a better condition of vegetation, leading to lower ground surface temperature in summer and higher ground surface temperature in winter. The ground surface freezing index ranges from 851.9 to 1906.6 °C·d and is averaged at 1253.3 °C·d, the frost day on the ground surface varies from 54 to 219 d with an average of 137.1 d, and the ground freezing index is slightly correlated to elevation and latitude. The ground surface thawing index ranges from 388.4 to 1727.2 °C·d, with an average of 1039.3 °C·d, and the thawed day on the ground surface ranges from 61 to 156 d, with an average of 128.8 d. The ground surface thawing index is negatively correlated with elevation, latitude, and longitude. Furthermore, the influence of elevation and NDVI on the thawing index is the largest. The onset date of ground surface thawing is greatly affected by topography and local factors, occurring mainly from mid-March to mid-May, the spatial heterogeneity of the onset date of ground surface freezing is less than the onset date of ground surface thawing, and the onset date of ground surface freezing occurs from the end-September to end-October. The thawing N-factor (Nt) ranges from 0.87 to 1.60, which is mainly concentrated at 1.2 to 1.5 with an average of 1.29±0.21. The freezing N-factor (Nf) ranges from 0.49 to 0.90, which is mainly concentrated at 0.5 to 0.65 with an average of 0.60±0.18. The ALT calculated with the classic Stefan Equation ranges from 0.99 to 2.72 m with an average of 1.68±0.45 m, which is influenced by dense vegetation and fine-grained saturated substrates. The correlation between the calculated and observed ALT is 0.886, with a deviation from 0.026 to 0.547 m. The monitoring network of ground surface temperature and relevant findings in this study could provide fundamental data and scientific evidence for the alpine ecological environment, thus likely facilitating the study of accurate mapping of high-elevation permafrost in the Headwater Area of the Yellow River.

Understanding the mechanisms of regional climate evolution requires extensive research on long-term urbanization and meteorological elements. The various data sources and an interactive interpretation method were utilized to reproduce the urban expansion in Beijing over the past century. The relationship between urban development and regional climate change was then determined by using the moving average method and the Mann-Kendall trend test. We found that the area of urban land in Beijing increased 64.48 times from 1916 to 2020, expanding in a circle around the central region. The rate of urban expansion peaked at 70.12 km²/a between 2000 and 2010. The average annual temperature and precipitation from 1916 to 2020 in Beijing were 12.25 ℃ and 588.6 mm, respectively. The 5-year moving average temperature fluctuated upward by 0.22 ℃/10a over the past century, with a notable warming trend since 1978. Precipitation trended downward at a rate of 9.37 mm/10a. The accelerated expansion of the impervious surface area in the city might lead to urban warming by altering the surface energy balance. The rate of urbanization and the regional temperature rise were positively correlated, with urbanization accounting for 20.83% of the regional warming in Beijing. Changes in the surface energy balance and an increase in air pollution emissions might result in a decline in precipitation. The results provide scientific resources for advancing knowledge of the processes and mechanisms by which urban development influences the regional climate change.

Land use, land-use change, and forestry, also known as LULUCF, are significant sources and sinks of carbon. A high-precision carbon accounting system for LULUCF should always be established as the primary building block for advancing low-carbon land use and sophisticated land management. This study uses the stock-difference method to account for carbon sources and sinks brought by LULUCF at the plot scale in Guangdong. According to the carbon accounting based on the surveys on soil, land use, and forest resources, Guangdong's LULUCF produced 29.673 million tons of carbon sinks in 2018, of which the biomass carbon sink contributed approximately 70% and the soil carbon sink around 30%. The major ways to increase LULUCF carbon sinks, therefore, are to increase plant cover and improve forest management. Different areas within the same land-use type have various carbon accounting values. Even within particular land-use types, such as forestland, wetland, cropland, settlements, and grassland, the carbon accounting values may fluctuate between being recognized as carbon sources and carbon sinks. In the era of reaching carbon peaking and carbon neutrality goals, it is difficult to meet the land-use management requirements with a carbon accounting technique assuming the carbon emission coefficient of every land-use type is constant. The carbon accounting of LULUCF in this study takes annual fluctuations in biomass and soil organic carbon pools into account, which complies with the United Nations Framework Convention on Climate Change criteria and is applicable on a national level in China. Meanwhile, the vegetation allometric growth model and the differentiation map of annual fluctuations of the soil carbon pool resulting from this study can be utilized to enable multi-scenario analyses of the carbon sources or sinks of lands at the plot scale. Finally, the results of the LULUCF carbon accounting offer some support for policymaking that emphasizes decreasing carbon sources and increasing carbon sinks in the management of land use and natural resources.

The space on the 30-150 m scale in the urban-rural transition zones belongs to an urban grass-roots space system that has obvious changes in development. In this paper, a multifractal analysis is carried out to reveal the evolution law of these zones, and the construction lands in Zhengzhou, Hangzhou and Beijing are taken as examples. Specifically, this study presents the multifractal characteristics by dividing three spatial evolution subsystems, according to generalized and typical f(a)-a(q) curve. Therefore, this paper makes a quantitative analysis of the spatial multifractal characteristics, taking the courtyard group level-neighborhood committee level space in the urban-rural transition zone as the research scale interval. The analysis shows that, the evolution of the zones belongs to adaptive change which is under the influence of macro-middle space, so its market-driven overtones are striking. On the whole, the evolution of grass-roots space is complicated in the rural-urban transition zone. Within a certain scale interval, generalized and typical spatial multifractal characteristics and their corresponding patch density (q) distribution areas are formed. Moreover, the evolution intensity of multiple spatial subsystems is usually different under the influence of various development processes and other factors, and their spatial composition also presents dynamic changes at various scales. And so, the spatial evolution of this zones is "situational". However, the grass-roots space of urban-rural transition zone is not a necessary continuation process from small and medium cities→traditional metropolises→modern metropolises→megacities. Its changes should be related to the status of the city in the urban system, more with the specific situation of urban-rural integration. The theoretical contribution of this paper is, to extend the typical multifractal characteristic system to more extensive evolution characteristic and degradation characteristic systems on the basis of satisfying the global and local indices. Thus, the nonlinear description of real development state of geographic space is enhanced.