Multifactor response
It is difficult to achieve maximum ESV and adjust all socioeconomic factors to the optimum intervals because of the complex coupling influence. We attempted to select several sets of factors with significant interactions to identify which proportions could regulate them for the purpose of maximizing ESV. As a result, “the proportion of construction” and “population”, “1st industry output value” and “population”, and “industrial water consumption” and “industrial electric consumption” were chosen to analyze how they cooperatively influence ESV.
This approach suggested that ESV is most affected by the population (Figure 3a). The population within 4 km2 should be controlled to be less than 20 k or approximately 120 k. In addition, ESV dropped sharply with the increase in construction land when the population was 50 k. In contrast, ESV declined slowly with the increase in construction land when the population was more than 100 k, which suggests that a relatively single distribution of construction land will not place too much pressure on the ecosystem in densely populated centers. However, controlling construction land still has a positive influence on ESV. Therefore, the city center can sacrifice nonconstruction land for infrastructure construction and population accommodation, and it will be necessary for it to reserve ecological space.
The surface of “1st industry output value” and “population” showed that there were two scenarios that achieve higher ESV (Figure 3b). One scenario was when the population was nearly 0 and the output of the 1st industry was more than 15 million CNY. Under this scenario, the object region had a small population but played an important role in agricultural production. The other scenario was when the population was approximately 150 k and the 1st industry output value was less than 10 million CNY.
Regarding energy consumption, “industrial water consumption” was presumably the limiting factor compared with “industrial electricity consumption” (Figure 3c). Industrial water consumption should be kept below 15 kt if one hopes to achieve a high ESV. When industrial electricity consumption was between 400 and 600 kw, ESV rapidly decreased with increasing industrial water consumption. This finding suggested that water consumption needs to be restricted and reserved in industrial areas.