As a fundamental energy consumption base in China, the Beijing-Tianjin-Hebei (BTH) region has experienced an increasing demand for clean energy in recent years. Photovoltaic power generation is a key for accelerating the transformation of energy infrastructure in China and achieving the goal of carbon neutrality during the 14th Five-Year Plan period (2021-2025). Taking the BTH region as a study area, we construct a comprehensive evaluation index system of "terrain-weather-cost" to calculate a photovoltaic development suitability index. We subsequently analyze the spatial pattern characteristics of photovoltaic development suitability in the study area in 2018 and quantitatively examine power generation potential and emission reduction effect under different scenarios of photovoltaic development suitability. Results indicate that: (1) The suitable areas for photovoltaic development account for 22% of the total area of this region, and the largest portion of this area is moderately suitable for photovoltaic development. The "Yanshan-Taihang mountains" line geographically divides the areas that are suitable and unsuitable for photovoltaic development, and a range of potential areas are distributed in prefecture-level cities of Chengde, Zhangjiakou and Baoding. (2) Photovoltaic power generation in the BTH region has great potential. Specifically, the annual power generation potential of the extremely and highly suitable areas is about three times more than the total power consumption in the same year of 2018. (3) The energy-saving and emission reduction effects of photovoltaic power generation are remarkable. If the extremely and highly suitable areas are used for photovoltaic development, there will be an approximate 47% reduction in carbon emissions across the whole region, according to the data of 2018. (4) Despite being restricted by limited land resources and the absence of an advanced transmission network or energy storage system, large-scale photovoltaic development is still a viable solution to energy supply issues. It still improves energy infrastructure, achieves the goal of carbon neutrality, and enhances the well-being of citizens in the context of global climate change and the new low-carbon economy.

The study of carbon budget and carbon compensation zoning from the perspective of major function-oriented zoning is of great significance for formulating low-carbon development strategies for each functional area, promoting the collaborative governance of regional ecological environment and achieving high-quality development, as well as an important contribution of geographical thinking to the realization of emission peak and carbon neutrality. This paper first constructs the theoretical framework of carbon budget and carbon compensation from the perspective of major function-oriented zoning, and then takes 157 county-level units of Beijing-Tianjin-Hebei Urban Agglomeration as the study area, and introduces the Concentration Index, Normalized Revealed Comparative Advantage Index and the SOM- K- means model to study the spatio-temporal differentiation of carbon budget and carbon compensation zoning of Beijing-Tianjin-Hebei urban agglomeration from the perspective of major function-oriented zoning. The study puts forward a spatial optimization scheme of carbon emission reduction oriented by low- carbon development. The results show that: (1) From 2000 to 2017, the carbon budget of the study area shows an upward trend of volatility, and its centralization index is higher than the "warning line" of 0.4, and overall, there are large regional differences. (2) There are significant regional differences in carbon budget, and carbon emissions show a core-periphery spatial pattern with Beijing-Tianjin-Tangshan as the main high-value center with a gradually decreasing outward; however, the spatial pattern of carbon absorption tends to be stable, showing an inverted "U-shaped" pattern, which is high in the east, north and west, and low in the middle and south. (3) The carbon budget of the study area is consistent with the strategic positioning of the major function-oriented zoning. Optimized development zone and key development zone are the main pressure-bearing areas of carbon emissions, while key ecological functional zone is the dominant area of carbon absorption. The difference of carbon absorption centralization index among functional zones is smaller than that of carbon emission centralization index. (4) There are 53 payment areas, 64 balance areas and 40 obtaining areas in the study area. Combined with the strategic objectives of the major function-oriented zoning, 9 types of carbon compensation space optimization areas are finally formed, and the low-carbon development directions and strategies are proposed for each type of area. (5) In the future, it is urgent to strengthen the research on carbon balance and horizontal carbon compensation in a more micro scale, enrich the theoretical framework of regional carbon compensation, integrate regional horizontal carbon compensation into the carbon trading market, and explore the diversified paths so as to achieve the goal of emission peak and carbon neutrality.

Under new international and domestic situations, scientific analysis of China's cultivated land quantity and its protection ways is of great significance for ensuring national food security and sustainable resources and environment development. This paper analyzes the amount of cultivated land under the constraints of multi-scenario food security within shared social-economic paths (SSPs), using model methods such as cultivated land retention, population forecast, food demand estimation, and yield potential decay. According to the multi-dimensional urgency assessment framework based on productivity characteristics-health status-farming, China's resilience-space for cultivated land protection is delineated by coupling the quantitative boundary control of time series and the regional rules of spatial scale. On the premise of satisfying the assumption of individual basic nutrition security and the constant variables of crop yield conditions, we obtain the following findings. (1) China's multi-scenario cultivated land retention will decline from 2020 to 2100. Existing cultivated land is sufficient to maintain long-term food security, but it barely reaches the critical range of theoretical food security (140 million-159 million hm²) in the short term. (2) The urgency of cultivated land protection in different dimensions presents different distribution characteristics within the nine agricultural zones. The North China Plain and the Middle-lower Yangtze River, which have superior natural conditions suitable for farming, are clusters of high-value plots of comprehensive urgency. (3) The sustainable scenario (SSP1) and the regional conflict scenario (SSP3) represent the minimum and maximum cultivated land retention scenarios under the constraints of food security bottom line. Given the current international situation, China should ensure that the short-term (before 2035) fallow land is not higher than 9.29%. (4) The resilience-space of cultivated land protection delineated based on time and space coupling can be divided into priority protection area, strict control area, rest area, strategic reserve area, comprehensive consolidation area, and special protection area. The flexibility, objectives and tasks of cultivated land protection in different divisions have their priorities. Overall, delineating resilience-space for cultivated land protection facilitates the establishment of spatial planning systems for cultivated land, such as agricultural structure adjustment and fallow policy improvement. This study provide a reference for research on the transformation of China's cultivated land protection system.

It is of great theoretical and practical importance to measure and examine tourism ecological security in the Yellow River Basin (YRB). The purpose of this study is to promote coordinated and sustainable development of the tourism economy and ecological environment. From the perspective of watershed sustainable development, this paper constructs the theoretical framework and index system of tourism ecological security in the YRB based on DPSIR system model, and analyzes its dynamic evolution characteristics and driving factors by using improved TOPSIS method, kernel density estimation, spatial autocorrelation, traditional and spatial Markov chains and quantile regression panel method. The results showed that: (1) There has been an evolutionary trend toward a dual-core form of tourism ecological security over time, as its average value fluctuates and then rises. The overall tourism ecological security level was relatively low (0-0.55), shifting from the predominant risk level in 2008 (accounting for 89.04%) to the levels of predominant risk and deterioration in 2017 (60.27% and 31.51%, respectively). A large downward risk remains. (2) In terms of dynamic evolution characteristics, the transfer of tourism ecological security risks and sensitive levels had "path dependence" and "self-locking" effects. In practice, however, the probability of maintaining the initial state of the deterioration level and the critical safety level was relatively small. And the type of transfer was usually accomplished during a subsequent level transfer. Its dynamic change process was strongly influenced by regional factors. Its characteristics of dynamic evolution were characterized by significant spatial and temporal heterogeneity. (3) Tourism ecological safety was most significantly influenced by environmental pollution in lower-level units. The tourism load level had a greater positive marginal effect on higher-level areas; however, economic development and level of tourism development have a greater positive marginal effect on areas with lower ecological tourism security levels.

Clarifying the changes of spatio-temporal pattern of ecosystem services and dividing the ecosystem service function zoning will help to achieve the fine management of land resources. The study took Wenshan city, a typical area in the karst mountainous southeastern Yunnan, as an example. We identified six types of ecosystem services in Wenshan from 2000 to 2017, namely, the food supply, water production, net primary productivity of vegetation, soil conservation, habitat quality and tourism culture. Then we examined their spatio-temporal patterns and differentiation characteristics. In addition, we used K-means clustering method to identify ecosystem service bundles and ecosystem service functional zones, and proposed differentiated ecological management measures. The results show that: (1) From 2000 to 2017, all the ecosystem services in Wenshan showed an upward trend, with the exception of the habitat quality service. (2) In terms of spatial distribution, the high-value areas of the six types are concentrated in the west and south, while the low-value areas are concentrated in the north and central parts. There are differences in the spatial distribution of hot and cold spots of the six types of ecosystem services, but they overlap on the whole except for the hot and cold spots of tourism culture service, which account for 2.56% and 0%, respectively, the areas of cold and hot spots account for 21% to 32% for the other five types. Only a small number of regions can provide three or more high-value areas of ecosystem services at the same time, and 85.50% of the regions can only provide two or less high-value areas. (3) According to the cluster results of ecosystem service bundles, Wenshan city could be divided into four types of ecosystem service function zones: ecological protection area, ecological transition area, main agricultural production area, and human production and living area. Differentiated ecological management and control suggestions are proposed for each functional area. The research results can provide references for resource utilization and space management in other Karst mountainous cities.