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Economic development and land-use change can strongly affect terrestrial ecosystems’ carbon balance. This paper quantifies the changes in land use of Yangtze River Delta urban agglomeration (YRD) in 2020 and 2035 under three economic growth scenarios, exploring the concurrent impact on carbon storage. The results showed that the land carbon storage of YRD had decreased by 1453.80 Tg in 2000–2020, and will continue to decrease by 982.38 Tg, 1417.62 Tg, and 1636.21 Tg under the scenarios of a slow, medium, and rapid economic growth from 2020 to 2035, respectively. The large-scale occupation of cultivated land and woodland for construction land caused by economic development and population growth was an important reason. The occupation of cultivated land by construction land in Nanjing, Shanghai, and its surrounding areas had further intensified, while the reduction in carbon storage caused by the reduction in woodland had become more prominent in Hangzhou, Shaoxing, Jinhua, and the surrounding areas.

High-speed rail (HSR) increases the non-local connections in cities and plays an essential role in urban land use efficiency. This paper uses a multi-period difference-in-difference model and a threshold model based on sample data that cover 284 Chinese cities from 2003–2018 to investigate the impact of HSR on urban land use efficiency. The results show that there is a 0.021 increase in urban land use efficiency after opening the HSR. The number of HSR stations and routes can increase the urban land use efficiency by 0.004 and 0.013, respectively. Compared with the cities in the East, the midwestern ones are more vulnerable to the impact of HSR. In particular, the positive impact of the number of HSR stations on the urban land use efficiency in cities with an urban population density exceeding 795 person/km2 is two times larger than cities with an urban population density of less than 795 person/km2. In addition, the impact of the number of HSR routes on urban land use efficiency in cities with an urban population density of less than 1003 person/km2 is five times larger than that of cities with an urban population density exceeding 1003 person/km2.

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With the rapid development of urbanization, the demarcation of the urban development boundary (UDB) is of great practical significance to curb the disorderly spread of urban land, avoid losing control of urban development space, and build a barrier to green development space. In this paper, we propose a method to support the demarcation of the UDB by combining the Maxent model and the cellular automata (CA) model. This approach comprehensively considers the relationship between urban construction suitability, neighborhood effect, spatial constraint, and random interference based on a spatio-temporal dynamic simulation. This contributes to the analysis of the driving mechanism and distribution pattern of urban expansion. According to the principle of scale expansion and centralization, the simulation result is modified to demarcate the UDB. The following conclusions are drawn: the Maxent-CA model can intuitively reflect the driving mechanism and accurately simulate urban expansion in specific cities, which contributes to demarcating the UDB. Considering that this method fully embodies the principle of combining top-down and bottom-up approaches in the demarcation of UDB, we argue that the Maxent-CA model is of vital importance for the sustainable development of the living environment and is of great reference value for territorial spatial planning.