A Quantitative Study of Urban Economic Scale Constrained by Water Environmental Carrying Capacity
2013, 28 (11):
Environmental carrying capacity is an important constraint to regional sustainable development. It is the thresholds of the population size and economic scale that make the system of a regional environment support. In this article, a new method is proposed to study the threshold of urban economic scale constrained by water environmental carrying capacity. Regional water environmental carrying capacity can be quantitatively represented by the value of Gross Domestic Product (GDP), if the population size can be predictable in this region. This new method is primarily based on the Water Environmental Threshold Value Model, which is proposed for the first time in this article, as well as some statistical techniques. In this mathematical model, the threshold value of GDP constrained by water environmental carrying capacity at a regional level is a function of five independent variables: G=[(P + C)×kI + 0.1WI]/[kI×(1-RT)], where G denotes the threshold value of GDP at a regional level, P is the value-added in primary, C is the value-added in construction, WI is the goal of the total amount control of industrial pollutants, RT is the proportion of the tertiary industry in GDP, and kI is the amount of pollutant emissions per 104 yuan of industrial value-added. The statistical methods applied here include regression analysis, which is used for the computation of the parameters P, C, WI, RT, kI, and interval estimation, which is used for the analysis of the sensitivity and reliability of the model. Yangzhou City is taken as a case to compute the economic scale constrained by the water environmental carrying capacity in 2015. COD is chosen as a total amount control factor (COD≤56845 t/a). The values of P, C, WI, RT, and kI are 229.02×108 yuan, 228.45×108 yuan, 18132 t, 39%, and 0.39 (1.38) kg/104 yuan per unit of industrial value-added, respectively. The result of computation indicates that: 1) Taking into account the continuity of the policy of pollutant reduction (kI=0.39), the annual water environmental carrying capacity of Yangzhou City can achieve 8372×108 yuan in GDP, with a confidence level of 90% and a confidence interval of 7881×108 to 9030×108 yuan; 2) without considering the pollutant emission reduction policy (kI =1.38), the annual GDP at the regional level can reach only 2904×108 yuan; 3) When the total amount control goal is determined, the main limiting factors of economic growth are the pollutant emission intensity and the proportion of the tertiary industry. If the regional economic growth target touches 5070×108 yuan, then the COD emission intensity should be controlled to below 0.69 kg/104 yuan per unit of industrial value-added.
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