1. Introduction
Land use change is one of the main research elements of global environmental change and sustainable development [
1,
2,
3,
4]. It is not only a visual representation of land use pattern change but also affects ecological, environmental, and regional climatic changes [
5,
6,
7,
8]. Therefore, modeling and predicting land use changes and exploring their internal spatial and temporal mechanisms and rules are important for guiding future regional development and controlling the direction of land use development to achieve the goal of sustainable development.
Land use change has been a hot topic, and scholars have conducted different studies in this field in recent years [
9,
10,
11]. There is extensive and in-depth research on the spatial and temporal patterns [
12,
13,
14,
15], driving forces [
10,
16,
17,
18,
19,
20,
21], and dynamic models [
22,
23,
24] of land use change. With the development of human society and the economy, the conflict between human and land has become increasingly serious, and some scholars have paid more attention to the subject of the relationship between human and land [
25,
26,
27]. Some research outlines the concerns of how land use changes generated by the rapid increase in the population will negatively impact on the climate [
28,
29,
30,
31] and ecological environment [
32,
33,
34,
35]. Scholars have investigated the drivers of land use change at different spatial scales in China [
10,
12,
36,
37]; among them, most have studied the relationship between farmland and construction land [
17,
38,
39]. Overall, previous research indicates that significant land use changes have occurred globally over the past decades. Each country, region, and city have different patterns of land use and influencing factors. However, population increase and human economic development are generally considered the two most important influencing factors driving land use change [
4,
10,
40].
In terms of methodology, the simulation and prediction of land use change are currently dominated by model simulations. Among these, artificial neural networks (ANN) [
41,
42,
43], agent-based model (ABM) [
44,
45], meta-cellular automata (CA) [
43,
46,
47], economic models, Markov chains, and machine learning models [
48] are the main methods used for the simulation and prediction of land use change. Since each model has different advantages and disadvantages, there are more studies with multiple model coupling [
49,
50,
51,
52]. In recent years, more and more scholars have used urban CA to simulate real cities, mainly focusing on the simulation of urban expansion, and some scholars have tried to use CA for urban planning For example, Li et al. [
53,
54,
55,
56] proposed a CA–Markov model based on an artificial neural network and ant colony algorithm. Kheder et al. [
57] combined genetic algorithms with meta-cellular automata and showed the significant effectiveness of the method. Overall, the coupled CA–Markov model effectively combines the advantages of the Markov long-term series simulation and powerful complex spatial prediction capability of CA [
58,
59,
60], while adding a multi-criteria evaluation mechanism (MCE) to generate a land suitability atlas [
61] to make the simulation and prediction results more informative.
As an important city in the central region of China, Zhengzhou city has experienced rapid economic development and drastic changes in land use in recent years [
62]. With the Zhengzhou Airport economic experimental zone becoming a national strategy supported by the construction of the Zhongyuan Economic Zone, Zhengzhou, as the core city of the Zhongyuan Urban Agglomeration, has gained significant development opportunities. Against the background of rapid urban development, the land use types in Zhengzhou are frequently transformed among each other, and the contradiction between human and land gradually emerges and these changes are a dynamic process [
63]. Therefore, it is of fundamental importance to study the characteristics of spatial and temporal changes in land use in the Zhengzhou metropolitan area and explore its change patterns and trends to solve current problems related to the sustainable development of megacities. In the present study, we examined the characteristics of land use change in Zhengzhou from 1980 to 2015 using remote sensing images and other auxiliary data to analyze its driving forces. Moreover, the spatial and temporal land use changes and evolution patterns in 2015 were simulated using the CA–Markov model with MCE suitability factors for predicting future changes. The results of this study can provide scientific support and a theoretical basis for land use planning and management, urban construction, and sustainable development of government departments, and they have implications for the development planning of mega-city clusters in China.
4. Discussions
The land use system is a complex system. This study constructed relevant factors affecting land use change from land adaptation variables and socio-economic variables; however, there still remains some difficulty in quantifying certain factors. Different choices of variables and indicators can lead to differences in simulation results. There-fore, the adequate selection of more scientific impact indicators is of great significance for future research in this field. In this study, between 1980 and 2015, there has been a significant shift in construction land use in Zhengzhou, with a large portion of farmland replaced by construction land; a similar situation was observed in Beijing from 1978 to 2013 [
71], Shenzhen from 1988 to 2015 [
72], and most cities in China [
10,
15,
73]. This suggests that economic development takes precedence over agricultural development in urban expansion. Between 2000 and 2005, construction land in the Zhengzhou metropolitan area grew rapidly (
Figure 2). In addition, between 2010 and 2015, the main urban area of Zhengzhou experienced a decline in construction land and increase in green space. Construction land in the surrounding cities of Zhengzhou, such as Zhongmu and Xingyang, maintained an increasing trend, suggesting that the expansion of urban space driven by policy planning during urbanization of Zhengzhou was completed at this stage, and the government began to focus on greening and environmental improvement of the city. Other cities will maintain the rate of expansion due to slower urbanization. The urban expansion pattern of the Zhengzhou metropolitan area shares characteristics with the early development of Chinese cities. From 2000 onwards, government departments began to work on planning for larger urban agglomerations; urban agglomerations near ports and rivers, such as those in the Yangtze River Delta [
74,
75,
76] and Pearl River Delta [
77], all showed a tendency to expand along rivers and near ports in the early years of urban expansion. The Zhengzhou metropolitan area is in the central region and has flat topography, which makes it cheaper to transform unused land and farmlands into urban areas, which can effectively reduce construction costs and facilitate urban expansion.
Land use in the Zhengzhou metropolitan area is influenced by a combination of factors, such as population growth, economic development, urbanization, ecological protection, land use policies, topography, slope, and climate change. The degree of influence of different factors on land use change varies greatly. In this study, it is argued that socioeconomic development is the dominant driver of land use conversion into construction land in the Zhengzhou metropolitan area. These results are consistent with previous studies [
62,
78]. The statistics in this study show that from 1980–2015, the population and economic growth in the Zhengzhou metropolitan area showed a significant positive correlation with the expansion of built-up land. The results of the PLUS analysis further indicate that the expansion of built-up land was significantly (
p value is 0) associated with population and economic growth.
Figure 10 shows that the areas with relatively rapid expansion of built-up land and economic growth were mainly located in Zhengzhou, Kaifeng, Xinxiang, and the strip between Zhengzhou and Xuchang. The areas with relatively slow land expansion and economic growth in the built-up area were mainly located in Jiaozuo and the western part of Zhengzhou.
Since 1980, the population of Zhengzhou has grown rapidly, and as the economy has grown and urbanization has increased, the rural population has gradually migrated to the city center. The population growth within the city has reduced the land area per capita, and the new population inevitably requires new carrying space, thus generating a strong demand for construction land and driving the rapid expansion of built-up areas [
79]. Further analysis showed that the driving force of population growth on the expansion of construction land is gradually weakening from the core of Zhengzhou outwards. In contrast, economic growth has been the main driver of urban construction land expansion. High elevation has a large impact on the conversion of farmlands to woodlands in the southwestern region. This is closely related to the policy of returning farmlands with slopes greater than 25° to forests, implemented by the Henan provincial government since 2000 [
10,
80]. In addition, temperature and precipitation are important drivers of the conversion of grasslands to farmlands in the Zhengzhou metropolitan area. During these 35 years, the beach lands along the north and south sides of the Yellow River were converted to farmlands. The Yellow River is the main source of freshwater in the Zhengzhou metropolitan area, and the farmlands are extremely dependent on water resources; the degree of water resources exploitation directly affects the change in the trajectory of the expansive farmlands. In terms of elevation, the lower plains in Henan province are suitable for agricultural production, and the lower the elevation, the more pronounced the expansion of farmlands. The economic development of the areas along the Yellow River is generally higher than that of other regions, particularly in Zhengzhou and Xinxiang, which are important cities in the Central Plains Economic Zone. The demand for construction land continues to increase, causing the stripping of a large amount of farmland resources.
Meanwhile, rapid economic development brought about by accelerated fixed asset investment is a direct driver of land use change in China [
81]. Construction land is an important component of fixed asset investment [
82], and its source has increased the intensity of land use and, on one hand, expanded urban space and, on the other hand, transformed from larger areas of farmlands. In terms of industrial structure, from 1980 to 2015, the proportion of tertiary industries increased considerably, and the proportion of primary and secondary industries decreased markedly. The outward shift of the secondary industry and adjustment of the internal structure of the industry brought about the transformation of the land use structure and expansion of construction land, which further increased the conversion rate of farmlands.
Through simulation analysis, it was determined that the total farmland area in the Zhengzhou metropolitan area will decrease by approximately 2626 km² in 2035, with the main conversion being farmlands to construction land (and the conversion among other types of land uses will be in a relatively balanced state). The main regions where farmland changes are predicted are in the southern part of Xinxiang and township areas in the southeastern part of Zhengzhou. Since 2018, China has proposed and implemented a rural revitalization strategy, which sets long-term goals for the comprehensive revitalization of rural industries and promotes changes in the structure and function of rural land use. The rural revitalization strategy optimizes the spatial land use structure in rural areas, promotes the flow between lands, accelerates the economic development of rural areas, and improves urbanization. Zhou et al. [
10] also reported similar findings. The intervention of land policies will lead to a significant increase in the level of construction land in the future Zhengzhou metropolitan area, but the reduction of farmlands also poses a potential problem for food security. These findings can assist governments to understand the future land use changes in the Zhengzhou metropolitan area according to the natural development scenario and thus support land use decisions.
This study also has limitations that should be explored in future research. Construction land use change is a very complex activity that involves consideration of economic, social, governmental planning, and ecological governance factors. Firstly, although meta-cellular automata and Markov chains are more applicable model simulation methods, the internal mechanism of land use change is extremely complex, which contains far more influencing factors, such as population density and flow, GDP, policies, soil types. Secondly, for the selection of model parameters, a generalized 30 × 30 meta-cell size and 5 × 5 filter were used without considering the influence of the meta-cell size and filter on the prediction results. Thirdly, the entire study area was considered as a whole unit, and the simulation errors caused by internal differences were ignored. Lastly, although the methodology and results of this study can serve as a reference for similar work, it does not fully capture the special factors that characterize the development process of other cities, particularly coastal areas and areas with higher economic development. Subsequent studies are required to further analyze other factors and variables that influence the development of urban construction and determine the mechanisms of construction land expansion. As urban agglomerations grow, government planning becomes more influential in changing construction land use, while other growth and influencing factors become more complex. Factors affecting the expansion of construction land, such as the policy system, industrial structure upgrading, and urban planning, cannot be precisely quantified. Future studies should analyze the internal influencing factors by combining statistical analysis of data with field research to achieve better spatial prediction effects and provide a more reliable basis for rational land use planning and ecological protection.
5. Conclusions
Due to the relatively stable natural environment in the Zhengzhou metropolitan area, natural drivers will only slowly influence land use changes in the area over a long period. Combined with the actual situation, when exploring the drivers of land use change in the study area, only a quantitative analysis of drivers was performed for those criteria that could be quantified in the socioeconomic drivers. The results of this study found that arable land and construction land in the Zhengzhou metropolitan area have changed substantially between 1980 and 2015. Among these, the area of arable land decreased each year because large portions were converted into forestlands and construction land due to urbanization and the policy of returning farmland to forests. The factors affecting the conversion of arable land mainly include the population and GDP. In the simulation results, this study determined that the relationship between urban construction and agriculture will be challenged by the excessive expansion of construction land and a sharp decline in farmlands. The forecast results show that the overall land use structure in 2035 will still be dominated by farmlands and construction land, while the areas of woodland, grassland, water land, and unused land will tend to be stable and almost unchanged. The area of farmland will be relatively reduced, but the overall area could still be maintained at a certain level due to the protection provided by the basic farmland policy. The growth trend of construction land was more evident. The simulation showed that land use changes will be more active in the future, and the urbanization level of the study area will be higher.
From the above analysis, the strongest influence on land use change was determined to be the increase in the urbanization rate, resident population, or non-agricultural population. Among these, the influence of non-agricultural populations on the evolution of construction land was more evident, indicating that the increase in the urbanization level will cause the encroachment of construction land on agricultural land. At the same time, the increase in the urban resident populations can squeeze the original construction land, thus further promoting the change of construction land production. This study can provide a reference for land use decisions in urban metropolitan areas.