In this section, the ANN-CA model that passed the accuracy verification was used to simulate and predict the land use scenario in Ya’an City in the future, facilitating the analysis of the future land use evolutionary trend in the study area. Firstly, a hypothesis was proposed for the model, and simulation was performed under the premise of no significant changes in humanity, society, economy, and nature. Secondly, constraints against model operation were set and the ecological factor chart of Ya’an City was input into the model. A constraint that the land use types within the scope of a natural reserve are prohibited for transformation into construction land and cultivated land was set to protect the ecological environment in Ya’an City. Thirdly, the data of spatial influencing factors was input, and the neural network model was constructed based on land use data in 2008 and 2018 for training and extracting relevant laws. The CA parameters were set to simulate and predict land use situations in Ya’an City in 2028; the model was calibrated spatially and quantitatively. The offset between the calculated actual spatial centers of different land use types in 2018 and the calculated simulation space centers in 2028 was within the allowable range. Moreover, the land use prediction results in Ya’an City in 2028 were output when the errors between the quantitative prediction area based on the SD model and the simulation areas based on the ANN-CA model of four land use types (cultivated land, construction land, forest land, and grass land) in 2028 were lower than ± 5%. Finally, data of the spatial influencing factors, actual land use data in 2018 and simulated land use data in 2028, which were output in the previous step, were input into the model. A neural network model was constructed and trained to extract relevant laws. CA parameters were set to simulate and predict land use scenarios in Ya’an City in 2038. The model was calibrated spatially and quantitatively. The land use prediction results in Ya’an City in 2039 were output when the offset between the calculated spatial centers of different land use types in 2028 and 2038 was within the allowable range, and the error range between the quantitative prediction area based on the SD model and the simulation areas based on ANN-CA model of four land use types (cultivated land, construction land, forest land, and grass land) in 2038 was lower than ± 5%. The land use prediction results in 2028 and 2038 are shown in Fig. 9.
The system model in this study also simulated and predicted the evolution of urban construction land in Ya’an City. Urban construction land includes urban industrial land, urban tertiary industrial land, urban residential land, urban road and traffic facility land, and others. These urban construction land types increased from 851, 818, 989, 900, and 543 ha. in 2019 to 1870, 2872, 1053, 1552, and 1700 ha. in 2038, respectively. The area of urban tertiary industrial land in 2038 will be the largest, which agrees well with the predicted tertiary industrial development in 2038. The land use prediction results in 2038 are shown in Fig. 10–12. The prediction of different land use types in urban construction land can provide some references for urban development planning and policy formulation in Ya’an City.
The actual land use status in Ya’an City in 2018 was compared with land use simulation results in 2028 and 2038. It can be seen that the spatial location distributions of different land use types change slightly, indicating that the spatial center migration analytical method can calibrate the model very well. The prediction results of four land use types in Ya’an City in 2028 and 2038 based on the SD model were compared with simulation results based on the ANN-CA model, and the error was calculated. The results are shown in Table 4. Obviously, under the constraint of calculated results based on the SD model, the absolute error between simulation results based on the ANN-CA model and the predicted area based on the SD model of cultivated land, construction land, forest land, and grass land was lower than 5% in both 2028 and 2038.
Table 4
Prediction errors of land use areas in Ya’an City in 2028 and 2038
Years
|
2028
|
2038
|
Land use types
|
SD
(hectare)
|
ANN-CA
(hectare)
|
|error|
(%)
|
SD
(hectare)
|
ANN-CA
(hectare)
|
|error|
(%)
|
Cultivated land
|
50661
|
52204
|
3.05%
|
51809
|
53014
|
2.27%
|
Construction land
|
16488
|
16750
|
1.59%
|
22806
|
23097
|
1.26%
|
Forest land
|
570353
|
551341
|
3.33%
|
603948
|
596583
|
1.23%
|
Grass land
|
39382
|
41032
|
4.19%
|
39699
|
41513
|
4.37%
|
For better observation of the construction land expansion trend in Ya’an City, the construction land was extracted from the land use simulation results in 2028 and 2038 based on the chart of the land use status in 2018. The construction lands were stacked from top to bottom in 2018, 2028, and 2038, the results of which are shown in Fig. 13.
In Fig. 13, the yellow region represents the construction land area in Ya’an City in 2018, the blue region represents the construction land expansion area from 2018 to 2028, and the red region represents the construction land expansion area from 2028 to 2038. It is clear that the construction land in the central and eastern regions (Tianquan County, Lushan County, Yucheng County, and Mingshan District) and southern regions (Hanyuan County) expanded significantly. The regions with great expansion of construction land are mainly distributed along rivers and roads, fully reflecting the driving and radiation effect of roads and rivers on urban construction in Ya’an City. To inform decisions regarding the traffic road network in Ya’an City, attention was paid to providing theoretical references for the implementation of policies like water resource management and protection. Generally, the construction land in Ya’an City presented a law of expansion from the center to surrounding areas, which was consistent with the open development pattern of “Four-way expansion” proposed by Ya’an City during the 13th Five-year plan. This confirms that the simulated evolutionary results of the ANN-CA model under the SD constraint are relatively accurate and reasonable. They can provide planning departments with reliable references to formulate related policies.