4.1. Timing Analysis of Coupling Coordination
The coupling degree model is used to calculate the coupling degree of environmental regulation and GWRE in each province, and the following is the coupling degree of China and four regions, as shown in
Figure 1.
It can be seen from
Figure 1 that the average coupled value of national environmental regulation and GWRE ranges from 0.5461 to 0.6142 from the national situation, and its timing change characteristics show a volatility increase. From the average situation of the four regions, the coupling degree of environmental regulation and GWRE in the eastern region was relatively stable, where the minimum value was 0.5469 in 2002 and the maximum value was 0.6207 in 2019, and the coupling degree between environmental regulation and GWRE in the central region first increased slowly, and then the coupling degree showed a downward trend, where the highest value appeared in 0.5895 in 2019, and the minimum value appeared in 0.5547 in 2008. The overall upward trend of coupling between environmental regulation and GWRE in the western region is the most obvious. From 0.5342 in 2000 to 0.5999 in 2019, the minimum value for the period was 0.5295 in 2006, and the fastest increase was in 2011.The coupling value of environmental regulation and GWRE in northeast China is also obvious, from 0.5443 in 2000 to 0.6166 in 2019. The minimum value appeared at 0.5211 in 2008. The maximum value appeared at 0.6166 in 2019. In the study period from 2000 to 2019, the coupling values of environmental regulation and GWRE in each province were calculated according to the coupling degree model ranging between 0.1879 and 0.6704, and from the data of each province, most of the coupling degrees of each province were concentrated above 0.5000, mainly concentrated in the two stages of moderate coupling and high coupling, indicating that the interaction between provinces is strong.
Using the degree of coupling coordination to judge the sustainability of the coupling relationship between environmental regulation and GWRE is conducive to a deep understanding of the degree of correlation between them. The higher the degree of coupling and coordination between environmental regulation and GWRE, the higher the correlation and the stronger the benign promotion effect between them, otherwise, it may cause a vicious circle due to low correlation and they may hinder the development of each other. According to the coupling coordination degree model, the timing change graph of the coupling coordination degree in China and four regions is obtained, as shown in
Figure 2.
It can be seen from
Figure 2 that the improvement average coupling and coordination degree between national environmental regulation and GWRE is between 0.3868 and 0.6424, and the coupling coordination degree between environmental regulation and GWRE in various provinces in the region is obviously different.
Firstly, between 2000 and 2019, the coupling coordination degree of Beijing, Tianjin, Shanghai, Guangdong, Jiangsu, Fujian, and Sichuan was within the range of 0.6000 to 0.8401, and from the mean level, the average level of coupling coordination in Beijing was the highest, reaching 0.6956, which was at the forefront of the country. Shanghai, Jiangsu, Fujian, Guangdong, Tianjin, and Sichuan were the next six provinces, with an average of above 0.6215, 0.6174, 0.6170, 0.6153, 0.6145, and 0.6082, respectively, and Shanghai, Tianjin, Guangdong, and other provinces remained at a high level for a long time. The coupling coordination degree is above 0.5000 every year, indicating that the improvement system between them in these areas has been in the middle coordination stage for a long time and the effect of environmental regulation is relatively obvious. Further, under the effective support and drive of environmental regulation, China’s water resources have been effectively allocated and effectively utilized.
Secondly, the provinces with the mean degree of coupling coordination within the range from 0.5000 to 0.6000, including Hebei, Shandong, Zhejiang, Anhui, Shanxi, Henan, Hubei, Hunan, Inner Mongolia, Chongqing, Guangxi, Yunnan, Guizhou, Shanxi, Liaoning, Jilin, and Heilongjiang, which contained the largest number of provinces in this range according at 17 provinces. The mean coupling coordination degrees were 0.5967, 0.5848, 0.5494, 0.5500, 0.5953, 0.5943, 0.5757, 0.5804, 0.5584, 0.5774, 0.5664, 0.5886, 0.5148, 0.5411, 0.5996, 0.5018, and 0.5416, and the level of coupling and coordination between environmental regulation and GWRE in these provinces has been improved in the development of more than 10 years.
Finally, the provinces with the average coupling coordination degree within the range from 0.1000 to 0.5000 include seven provinces, including Hainan, Jiangxi, Gansu, Qinghai, Ningxia, Tibet, and Xinjiang, with values of 0.3869, 0.4811, 0.4628, 0.3400, 0.3815, 0.2767, and 0.4643, respectively. This shows that the level of regional environmental regulation and GWRE improvement is uneven, and the implementation effect of relevant policies is not as good as that in the eastern region; therefore, the matching degree between environmental regulation and GWRE improvement capacity is not high, and it is difficult for environmental regulation and GWRE to form a mutual promotion effect, and a benign level of interaction and coordination has not been achieved. However, from the perspective of regional development potential, there is still great potential for the coupling and coordinated development of these provinces. Therefore, according to the actual situation of the region, the government departments of each region should formulate policies that are in line with the coupling and coordinated development of the region and promote the coupling and coordination of environmental regulation and GWRE in the region as soon as possible to move to a higher level.
4.2. Spatial Analysis of Coupling Coordination
The average calculation of the coupling coordination degree between the factors in the three time periods of 2000–2009, 2010–2019, and 2000–2019 is calculated, as shown in
Table 5.
It can be seen from the relevant data in
Table 5 that the regional difference in the average coupling coordination degree between environmental regulation and GWRE at the provincial level in China is not too obvious; the average coupling coordinations of the three time periods in the eastern region from 2000 to 2009, 2010 to 2019, and 2000 to 2019 were 0.5716, 0.5996, and 0.5854, respectively, and the average values of the same three time periods in the central region were 0.5685, 0.5754, and 0.5725, respectively; the average values of the same three time periods in the western region were 0.5464, 0.5865, and 0.5633, respectively; and the average values of the same three time periods in the northeast region were 0.5376, 0.5546, and 0.5464, respectively. The national averages for the three same time periods were 0.5571, 0.5837, and 0.5721, respectively; the average values are basically in the range of 0.5000 to 0.6000, and at the same time, the overall trend of the average of coupling coordination is rising, but not too high. From 2000 to 2009, except for Beijing, Shanghai, Tianjin, Chongqing, and Guizhou provinces, the average coupling coordination degrees were 0.6321, 0.6032, 0.6168, 0.6072, and 0.6063, respectively. Their average values exceeded 0.6000, the average values of other provinces were basically maintained in the range of 0.5000 to 0.6000, and the coupling coordination showed an upward trend, although the coupling coordination value decreased in some years, such as in Hainan where the coupling coordination values were 0.4658 and 0.4072 in 2001 and 2002, below 0.5000. From 2010 to 2019, the provinces with an average coupling degree of coordination of more than 0.6000 included Beijing, Shanghai, Tianjin, Chongqing, Jiangxi, Guangxi, Guizhou, and Shaanxi, and the average of other provinces remained basically within the range from 0.5000 to 0.6000.
In general, between the years of 2000 and 2019, the regions where China’s coupling coordination improved more rapidly were in the eastern and central regions. Between the years of 2010 and 2019, most provinces in the eastern region continued to improve, while the coupling coordination degree in most parts of China’s western region and northeast region also increased significantly. Tibet and Qinghai in the western region and Liaoning in the northeast were particularly prominent. The mean coupling coordination degree increased from 0.2637, 0.4735, and 0.4946 in 2000–2009 to 0.5463, 0.5743, and 0.5082 in 2010–2019, respectively, exceeding 0.5000. The coupling coordination degree shows a certain gradient change trend in China’s space, and the coupling coordination degree of the whole country shows a spatial pattern of “step-by-step decline in the east, central, northeast and west”, but the polarization is not very obvious. From the perspective of the trend of coupling and coordinated changes in China, the scientific research level, high-quality talents and the concentration of science and technology industries in the eastern coastal areas were relatively high compared with the inland areas and have superior resources endowments and geographical location advantages. Under the spillover of technical knowledge, technological innovation can be effectively carried out at the same time. Under the tilt of the macro policy of the national and environmental science and technology department policies, environmental regulation, and GWRE improvement have seen benign resonance, which is conducive to promoting the improvement of coupling and coordinated development of environmental regulation and GWRE in China.
4.3. Convergence Analysis of Coupling Coordination
According to the coupling coordination degree theory, the convergence of the coupling coordination degree between environmental regulations and GWRE is examined, and the convergence between the two is analyzed. Absolute β convergence indicates that the coupling coordination degree in the model shows the same convergence trend, and the conditional β convergence indicates that the trend is not exactly the same and there are specific steady-state conditions. According to the treatment method of Barro et al. (1992) [
50], the absolute β convergence model is designed as the Formula (5):
In Formula (5), d
i0 and d
it represent the coupling coordination degree at the beginning and end of the period i (i = 1, 2, …, 31) in each province, T represents time, α represents the constant term, ε
t represents the random perturbation term, β represents the convergence coefficient, β < 0 represents the coupling coordination degree of environmental regulation and GWRE tending to converge, and β > 0 represents that there is no convergence. In convergence detection, if it is found that the test results do not exist for β convergence, then some control variables can be appropriately increased or decreased, and then the convergence test is performed. For β < 0, it can be considered that there is a condition of β convergence. At the same time, for the condition of the β convergence detection model, Formula (6) is constructed:
In Equation (6), d
it and d
i(t−1) represent the level of coupling coordination between environmental regulation and the GWRE improvement system in phase t and phase t − 1, α, β and ε
t explained in the same Formula (5). If β < 0, this indicates that the level of improvement of coupling and coordination between environmental regulation and GWRE tends to converge, and oppositely, there is no convergence. According to Formulas (5) and (6), the convergence test and analysis of the coupling coordination level above were carried out, and the results are shown in
Table 6.
Under the test of absolute β convergence, it is shown that the β value is greater than zero, and it passes the t-test at the significance level of 1%, which shows that there is no absolute β convergence at the level of coupling coordination between environmental regulation and GWRE. During the study period, and under the assumption that the initial conditions are the same, the coupling and coordination level discussed above in China is not a homogeneous development, but a differentiated development trend. Under the test of conditional β convergence, the regression coefficient of convergence coefficient β is also greater than zero, and the t test under the significance level of 1% is passed, indicating that there is no conditional β convergence of the two, and further conclusions are obtained. The coupling level of environmental regulation and GWRE in China shows a differentiated development trend.