3.1 Data source and preprocessing
When analyzing urban agglomerations, this paper constructs an index system of the ecological environment of urban agglomerations on the northern slope of Tianshan Mountain from three aspects: ecology, economic ecology, and social ecology. The data used in this study include: normalized difference vegetation index (NDVI) data(Yue et al., 2022): Landsat remote sensing images were selected as the main data in the three time periods of 2000, 2010, and 2018 Source, the data comes from NASA (https://gpm.nasa.gov/), the selected data seasons are the same, and the element status is relatively consistent, which ensures that the research is comparable and can meet the research accuracy requirements; Digital Elevation Model (DEM) data (Raczkowska and Cebulski, 2022): The spatial resolution is 90m×90m, and the data comes from the geospatial data cloud platform (http://www.gscloud.cn), which is spliced after downloading; temperature and precipitation data(Mao et al., 2022): source China Meteorological Data Network (http: / /data.cma.cn); population density data(Martin-Turrero et al., 2022): provided by the geographic and national conditions monitoring cloud platform (http://www.dsac.cn/); Social and economic statistical data were obtained from The Bureau of Statistics of Xinjiang Uygur Autonomous Region (http://www.xjtj.gov.cn/) (2000–2018) (Zibibula·Simayi et al., 2020). Extraction of soil PH value and soil organic carbon content(Cervera-Mata et al., 2022): Soil organic matter content data were provided by the World Soil Database (HWSD) (HTTP: //www. fao.org) (Wang et al., 2015). Extraction of land use types(Li et al., 2022): provided by Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences (http://www.resdc.cn), the data of 2000, 2010 and 2018 were selected (Wang and Su, 2018).
3.2 Data preprocessing
(1) DEM data: Obtain slope and topographic undulation data through the Surface and Neighborhood tools on the ArcGIS software platform.
(2) Comprehensive index data of land use degree: The comprehensive index of land use degree comprehensively reflects the degree of land use in a certain area. The calculation formula is shown in formula (1).
\({L}_{a}=100\times \underset{i=1}{\sum ^{n}}{A}_{i}\times {C}_{i}\) (1)
\({L}_{a}\in \text{100,400}\)
In the formula, La is the comprehensive index of land use degree; Ai is the grading index of land use degree of the i-th level; Ci is the area ratio of the grading land use degree of the i-th level.
(3) Meteorological data: The average annual temperature and annual precipitation are based on the data of 7 meteorological stations around the urban agglomeration on the northern slope of Tianshan Mountain. For precipitation, use Anusplin tool to complete the spatial interpolation of meteorological data.
(4) Socio-economic data: Population density is the total population/total area of each city (county); the proportion of the secondary industry is the total output value of the secondary industry of each city (county)/the total output value of the secondary industry of the city. For the socio-economic data, ArcGIS software is used to complete the inverse distance weight interpolation model.
The spatial visualization of index data can be realized by obtaining various index factors that characterize the quality of the ecological environment. Because the projection methods, coordinate systems, and scales of various data are not the same, the spatial resolution of all data is unified into a 1 km×1 km grid form, and the same Krasovsky ellipsoid coordinates and Albers projection are used. In order to calculate. For data with missing spatial attributes in data processing, it is obtained indirectly based on data collection technology on the basis of reference to existing research results. Then the natural ecological index (NE1), social ecological index (SEI) and economic ecological index (EEI) were calculated on the ArcGIS platform, and grid calculation was carried out. The natural fracture method is used to obtain the classification map of ecological environment quality evaluation, finally, the dynamic changes and influencing factors of the ecological environment quality of the urban agglomeration on the northern slope of Tianshan Mountain are analyzed, and the future development of ecological environment quality is predicted.
3.2 Rationality of indicators
The result of the long-term interaction of various natural, social, and economic elements in the regional ecological environment is the basis for the formation of the local conditions of the regional ecological environment(Eckenwiler, 2018). This research follows the basic principles of comprehensiveness, scientificity, systemicity, easy accessibility, independence, simplicity, etc.(Lin et al., 2021), and combines the ecological environment and social economy of the urban agglomeration on the northern slope of Tianshan Mountain, and selects 11 indicators to construct the northern slope of Tianshan Mountain. The evaluation index system of the ecological environment of urban agglomerations. Specifically: As a single indicator cannot reflect the relationship between urban agglomerations and the ecological environment, factors affecting the quality of the regional ecological environment(Komarova et al., 2021).
By verifying whether there is overlap of information among the 11 indicators, to ensure the accuracy of the evaluation results. Therefore, this study uses the method of multicollinearity diagnosis to make judgments(Mihreteab et al., 2020). Commonly used diagnostic indicators of multivariate collinearity mainly include variance inflation factor (VIF) and tolerance (TOL)(Sahani and Ghosh, 2021). These two indicators have a reciprocal relationship. When VIF < 10 (that is, TOL > 0.1, it indicates that there is no obvious multiple collinearity in the selected indicator(Arabameri et al., 2019). The specific method is: In ArcGIS, a 5km×5km fishing net is used to penetrate the entire boundary layer of the urban agglomeration on the northern slope of Tianshan Mountain, and a total of 5275 points are uniformly generated. With these points, 11 indicators and EQI values are read, and a collinearity diagnosis is calculated in SPSS The index (Table 1) is the statistics of these two indicators. Through the correlation test of all variables, the correlation coefficient between the variables can be observed from Fig. 3. The results show that there is no obvious collinearity among the 11 indicators, and there is no information overlap. Therefore, these 11 indicators are reasonable for this study.
Table 1
Results of multicolliearity diagnostics
Index
|
2000
|
2010
|
2018
|
VIF
|
TOL
|
VIF
|
TOL
|
VIF
|
TOL
|
p1
|
1.762
|
0.568
|
1.673
|
0.598
|
1.603
|
0.624
|
p2
|
9.281
|
0.112
|
1.547
|
0.646
|
1.242
|
0.805
|
p3
|
6.904
|
0.145
|
1.051
|
0.952
|
1.051
|
0.952
|
p4
|
1.561
|
0.64
|
1.571
|
0.636
|
1.403
|
0.713
|
p5
|
1.223
|
0.817
|
1.195
|
0.837
|
1.178
|
0.849
|
p6
|
1.338
|
0.748
|
1.343
|
0.745
|
1.365
|
0.732
|
p7
|
1.753
|
0.57
|
1.712
|
0.584
|
1.668
|
0.6
|
p8
|
1.225
|
0.816
|
1.19
|
0.84
|
1.194
|
0.837
|
p9
|
1.316
|
0.76
|
1.426
|
0.701
|
1.441
|
0.694
|
p10
|
1.018
|
0.983
|
1.058
|
0.945
|
1.018
|
0.982
|
p11
|
6.974
|
0.159
|
1.527
|
0.655
|
1.224
|
0.817
|
p1: NDVI; p2: Annual average rainfall; p3: Annual average temperature; p4: Surface undulation; p5: Distance to the river; p6: Soil type;p7: Soil effective water content; p8: Land use intensity; p9: Distance from road; p10: Population density; p11: The proportion of tertiary industry. The same below.
3.3 Ecological environment quality evaluation model
Evaluation indicators often have different dimensions, positive and negative terms, and the data vary greatly(Gottero and Cassatella, 2017). In order to achieve comparability, testability and ease of comparison among indicators, it is necessary to standardize the original data of each evaluation index before determining the weight of indicators(Pozsgai et al., 2021).
3.3.1 Natural ecological index spatial principal component analysis method, under the premise of ensuring the minimum loss of data and information, transforms multiple related indicators into a few uncorrelated comprehensive indicators by rotating the original spatial coordinate axis, which can maximize The information of the original indicators is reflected to the limit(Arabameri et al., 2019). At the same time, the whole process of spatial principal components does not need to artificially set weights, and the evaluation results are objective. Based on the above theories, this research is based on the ArcGIS platform and will evaluate in the index system, the ecological environment quality index, Surface undulation, annual average precipitation, annual average temperature, river network density, Soil type value, soil organic carbon content and other indicators related to natural ecology in the index system are analyzed by spatial principal component analysis to calculate the natural ecological index (NEI). The calculation formula is as follows:
$$NEI={R}_{1}{X}_{1}+{R}_{2}{X}_{2}+{R}_{3}{X}_{3}+···+{R}_{i}{X}_{i} \left(2\right)$$
In the formula: \({R}_{i}\) is the contribution rate corresponding to the i-th principal component; \({X}_{i}\)is the i-th principal component.
When the cumulative variance contribution rate is greater than or equal to 80%, it can replace most of the relevant information of the original data(Zemni et al., 2022). In order to obtain the natural ecological information of the urban agglomeration on the northern slope of Tianshan Mountain truly and objectively, the cumulative contribution rate of the first four principal component factors has reached more than 80% (Table 2). Therefore, this study selects the first four principal component factors for fitting calculation .
Table 2
Results of spatial principal component analysis
Principal component
|
eigenvalue
|
rate of contribution
(%)
|
Cumulative contribution rate(%)
|
2000
|
2010
|
2018
|
2000
|
2010
|
2018
|
2000
|
2010
|
2018
|
p1
|
2.187
|
2.194
|
2.175
|
31.238
|
31.337
|
31.071
|
31.238
|
31.337
|
31.071
|
p2
|
1.772
|
1.212
|
1.841
|
25.316
|
27.314
|
26.295
|
56.554
|
58.651
|
57.366
|
p3
|
1.125
|
1.06
|
1.174
|
16.078
|
15.144
|
16.772
|
72.632
|
73.795
|
74.138
|
p4
|
0.84
|
0.86
|
0.829
|
11.998
|
10.281
|
11.836
|
84.63
|
83.076
|
85.974
|
p5
|
0.53
|
0.714
|
0.568
|
7.57
|
6.194
|
8.109
|
92.2
|
89.27
|
94.083
|
p6
|
0.403
|
0.577
|
0.414
|
5.754
|
5.241
|
4.184
|
97.954
|
94.511
|
98.267
|
p7
|
0.143
|
0.384
|
0.116
|
2.046
|
5.489
|
1.733
|
100
|
100
|
100
|
3.3.2 Social Ecological Index The importance of social ecological index indicators is closely related to the amount of information. The coefficient of variation method starts from the attributes of the data and uses the standard deviation of each indicator as the amount of information. The weighted average is used to determine the weight of the indicator(Yang et al., 2022). It has an elimination dimension. The advantages of the weighting impact. Considering that the three indicators of social ecology-related population density, land use type, and road network density in the indicator system are difficult to determine the impact on the ecological environment of the basin, this study starts with Starting from the characteristics of the selected indicators, the weight is determined by the importance of the indicators, and the coefficient of variation method is used to calculate the social ecological index (SEI). The calculation formula is as follows:
$${V}_{i}={\sigma }_{i}/{\stackrel{-}{X}}_{i} \left(3\right)$$
$${W}_{i}={V}_{i}/\sum _{i=1}^{n}{V}_{i} \left(4\right)$$
$$SPI=\sum _{i=1}^{n}{W}_{i}{Y}_{i} \left(5\right)$$
Where: \({V}_{i}\) is the coefficient of variation of the i-th index; \({\sigma }_{i}\) and \({\stackrel{-}{X}}_{i}\)are the standard deviation and average of the i-th index, respectively; \({W}_{i}\)is the weight of the i-th index; \({Y}_{i}\)is the i-th index after indexing, which is used in this study To calculate the coefficient of variation and weight of the three indicators of SPI, as shown in the Table 3.
Table 3
Variation coefficients and weights of three indexes
|
2000
|
2010
|
2018
|
p8
|
p9
|
p10
|
p8
|
p9
|
p10
|
p8
|
p9
|
p10
|
Mean value
|
0.551
|
0.867
|
0.999
|
0.535
|
0.867
|
0.997
|
0.507
|
0.867
|
0.999
|
standard deviation
|
0.390
|
0.153
|
0.017
|
0.390
|
0.153
|
0.032
|
0.381
|
0.153
|
0.017
|
variable coefficient
|
0.708
|
0.177
|
0.017
|
0.729
|
0.177
|
0.032
|
0.751
|
0.177
|
0.017
|
weight
|
0.786
|
0.196
|
0.018
|
0.778
|
0.188
|
0.034
|
0.795
|
0.187
|
0.018
|
3.3.3 Economic ecological index Economic development will affect the changes of the ecological environment in surrounding areas to a certain extent. The indicators related to economic ecology in the index system are the proportion of the tertiary industry representing the economic development status of the basin(Jiang et al., 2021). To a certain extent, it can reflect the intensity of economic development on the environmental protection and capital investment in the surrounding areas. Therefore, the economic ecological index (EEI) in this study is equivalent to the proportion of the tertiary industry.
3.3.4 Eco-environmental quality evaluation index This research starts from the three aspects of nature, society and economy, and calculates NEI, SEI and EEI respectively to characterize the ecological environment quality status of the urban agglomeration on the northern slope of Tianshan Mountain. Combining the unique characteristics of the urban agglomeration on the northern slope of Tianshan Mountain Regional characteristics and the importance of the factors affecting the regional ecological environment are ranked from high to low: natural factors>social factors>economic factors(Ren et al., 2022).This study uses a hierarchical analysis(Zhong et al., 2022) to determine the weight of NEI, SEI and EEI.The specific method is: construct a pairwise discriminant matrix according to the interrelationship between the indicators, and then perform a consistency test, and finally calculate the weight value of each indicator. (Table 4) The discriminant matrix constructed based on this , The maximum characteristic root = 3.014, the consistency index CI = 0.007, the random consistency index RI = 0.520, the random consistency ratio CR .= 0.013<0.1, passed the consistency test(Jahanger, 2021). After calculation, the weights of NEI, SEI and EEI Respectively 0.570, 0.333, 0.097. The calculation formula of the eco-environmental quality evaluation index (EQI) is as follows:
$$EQI=0.570NEI+0.333SEI+0.097EEI \left(6\right)$$
Table 4
Pair-wise comparison matrix
Index
|
NEI
|
SEI
|
EEI
|
NEI
|
1
|
2
|
5
|
SEI
|
1/2
|
1
|
4
|
EEI
|
1/5
|
1/4
|
1
|
NEI: Natural ecological index ; SEI: Social ecological index ; EEI : Economic ecological index |
In order to compare and analyze the differences in ecological environment quality in local areas, it is necessary to classify the EQI. Here, this study mainly uses the natural break point method (Jenks) for classification(Guo and Yuan, 2021). The classification criteria for each period should be unified, otherwise no comparative analysis can be performed(Bjelle et al., 2021). Therefore, both 2000 and 2018 adopted the 2018 grading standard. The grading standards (Table 5) are shown.
Table 5
Classification criterion of eco-environmental quality
class
|
Criterion
|
EQI
|
1
|
Extremtly bad
|
༜0.425
|
2
|
Bad
|
0.425 ~ 0.491
|
3
|
Poor
|
0.491 ~ 0.556
|
4
|
Moderate
|
0.556 ~ 0.617
|
5
|
Better
|
0.617 ~ 0.675
|
6
|
Good
|
0.675 ~ 0.736
|
7
|
Excellent
|
༞0.736
|
2.4 Comprehensive Index of Ecological Environment Quality
The comprehensive index of ecological environment quality is an objective indicator to measure the overall condition of the regional ecological environment. The model is:
$$E=\underset{i=1}{\sum ^{n}}{P}_{i}\frac{{A}_{i}}{S}$$
7
In the formula: EEQI is the comprehensive index of ecological environment quality; Pi is the ecological environment level; Ai is the number of grids of the i-th level; n is the total number of levels; S is the total number of grids. The smaller the value of E in the study, the worse the overall ecological environment quality of the region.
3.5 spatial clustering model
Spatial autocorrelation analysis is to examine a certain geographical phenomenon or the overall dispersion state of a certain variable, and then determine whether it has agglomeration characteristics in space(Haak et al., 2022). The global spatial autocorrelation index is used to verify the spatial correlation index of a certain element in the entire research area. This paper selects the global Moran's I index index, and with the support of the GeoDa software platform, analyzes the agglomeration characteristics of the ecological environment quality index in 2000, 2010 and 2018 respectively, The calculation formula is as follows(5):
Global Moran’s I Index: \(I=\frac{\underset{i=1}{\sum ^{n}}\underset{j=1}{\sum ^{n}}{w}_{ij}({x}_{i}-\stackrel{-}{x})({x}_{j}-\stackrel{-}{x})}{\underset{i=1}{\sum ^{n}}\underset{j=1}{\sum ^{n}}{w}_{ij}\underset{i=1}{\sum ^{n}}({{x}_{i}-\stackrel{-}{x})}^{2}}\) (8)
Local Moran’s I Index: \(I=\frac{\left({X}_{i}-\stackrel{-}{X}\right)}{{S}^{2}}\sum _{j}{W}_{ij}\left({X}_{j}-\stackrel{-}{X}\right)\) (9)
In the formula, I represents Moran's I index; Xi and Xj represent the mean value of the ecological environment quality of the i-th and j-th grids; Wij refers to the spatial weight matrix.
Where I stands for Moran's I index; Xi and Xj stand for the mean value of the ecological environment quality of the i-th and j-th grids; Wij means the spatial weight matrix, S Represents the sum of the elements of the spatial weight matrix.
Based on the calculation of the global Moran's I index(Bai et al., 2021), the Moran scatter plot is obtained, and the ecological environment quality index is further divided into 5 different types, namely, high-high aggregation area (H-H), high-low aggregation area (H-L), low-high aggregation area (L-H), low low aggregation area (L-L) and not significant (No significant). The specific meaning is shown in Table 6:
Table 6
The connotation of different Moran clustering models
Clustering types
|
Connotation
|
High-High clustering ( H-H)
|
The spatial agglomeration characteristics of the region's own ecological environment and the surrounding level are high.
|
High-Low clustering ( H-L)
|
The region's own ecological environment is of high quality, but the surrounding area has low spatial agglomeration characteristics.
|
Low-High clustering ( L-H)
|
The fragility of the ecological environment of the region itself is low, but the surrounding area has high spatial agglomeration characteristics.
|
Low-Low clustering ( L-L)
|
The spatial agglomeration characteristics of the region's own ecological environment and the surrounding level are low.
|
No significant
|
There is no significant spatial agglomeration feature.
|
3.6 Geodetector
Geodetector is a new statistical method proposed by Wang Jinfeng to detect spatial differentiation and reveal its driving factors (Liu et al., 2021). This study uses a factor detector to analyze the causes of the ecological environment quality of the urban agglomeration on the northern slope of the Tianshan Mountains. The factor detector can detect whether a factor is the cause of the spatial and temporal distribution pattern of the ecological environment quality and to what extent it explains the space of the ecological environment quality. Differentiation mechanism, the specific method is: use EQI as the dependent variable, take the selected 11 indicators as independent variables, use the natural breakpoint method for stratification, and convert the numerical value to the type value. In ArcGIS, use the Create Fishnet tool to construct the fishing nets of 5 km×5 km cover the entire study area, and a total of 5275 fishing nets are uniformly generated. Then the dependent variable values and the independent variable values are matched through the fishing nets to detect the influence of each factor. Available Q value measurement, its expression is:
Q = 1\(-\frac{\sum _{h=1}^{L}{N}_{h}{\sigma }_{h}^{2}}{N{\sigma }^{2}} \left(10\right)\)
Where: h = 1,..., L is the stratification (Strata) of variable Y or factor X, that is, classification or division; N and N are the number of units in layer h and the whole area respectively;\(\sigma\)and \({\sigma }^{2}\) are layers respectively The variance of h and the Y value of the whole area. The value range of is [0,1], the larger the value, the more obvious the spatial differentiation of Y; if the stratification is generated by the independent variable X, the larger the value of q, the greater the influence of the independent variable ⅹ on the attribute Y Larger, conversely, smaller.
3. 6 CA-Markov model
Cellular automata (CA) is a mathematical model that can simulate the spatiotemporal evolution process of a huge complex system(Zhou et al., 2022). The model is:
$${S}_{ij}^{t+1}={f}_{q}\left({S}_{ij}^{t}\right)$$
11
In the formula: \(S\) is the state of the ij-th cell; t and t + 1 are moments; \(f\) is the transfer function; \(q\) is the neighborhood.
The basic principle of Markov is to realize the simulation prediction of its future development status by using the experience transfer probability of the existing discrete state of the system. If there is Markov property in the change process of a system, Se is its state at the initial moment, then the state after e cycles can be defined as:
$${S}_{e}={S}_{0}{P}_{e}$$
12
Where: \({S}_{e}\) is the state after e cycles; \(e\) is the number of cycles; \({P}_{e}\) is the system experience transfer probability matrix.
The research is based on IDRISI17. 0 software is used as a tool to calculate the probability matrix based on the data of 2000 and 2010, 2010 is the base period, the number of iterations is set to 8, the filter is 5 × 5, and the proportional coefficient is set to 0.15. The spatial pattern of the ecological environment quality in 2018 is simulated and compared with the actual ecological environment quality status in 2018. The CROSSTAB module is used to complete the calculation and accuracy verification of Kappa coefficients of real and simulated results. In the same way, complete the simulation forecast for the region in 2026.