1 Introduction
Since the 1970s, the rate of urban land sprawl in the world is generally higher than the urban population growth rate, which indicates that urban land is expanding rapidly
[1]. As the largest developing country in the world, China's urban land use is facing a severe situation in the world
[2]. The speed of land urbanization in China is greater than that of population urbanization. In the process of urbanization, especially, the continuous blind sprawl of China's big cities is one of the five most serious problems. Moreover, land urbanization is faster and the situation of land out of control is taking place
[3].
China's urban construction land has expanded rapidly, especially, the scale and speed of urban sprawl are unprecedented in the eastern coastal areas
[4]. In the 1990s, with the acceleration of industrialization, China's urbanization also entered quick development stage
[5], and large-scale population urbanization has also resulted in a large number of agricultural land conversions to urban land
[6]. From 1981 to 2002, China's urban construction land area expanded rapidly from 7, 438 to 25, 973 square kilometers
[7]. After 2000, with China's accession to the WTO and the improvement of urban development, the pace of urban construction and urban sprawl also accelerated further. However, the rapid can cause a large number of agricultural land loss
[8]. Moreover, most of the surrounding cities have the cultivated land of fertile soil and higher productivity, urban sprawl is bound to lead to loss of high-quality cultivated land and aggravates the contradiction between supply and demand of cultivated land
[9]. In addition, urban sprawl encroaches upon a large number of cultivated land and ecological land, which directly leads to a sharp decrease of quantity and quality of cultivated land and eco-environmental problems
[10]. Many domestic scholars have studied the impact of land use change and urban sprawl on ecosystem
[11-15], so the impact of urban sprawl on loss of cultivated land and ecosystem function has been confirmed. How to optimize the allocation of limited land resources and achieve the coordinated development of urban sprawl and ecosystem is a severe challenge for land use in China. On November 3, 2014, the Ministry of Land and Resources and the Ministry of Agriculture jointly released the Notice on Further Making the Work of Generally Permanent Land Use Planning, it is the first-time clear requirement for Beijing, Shanghai, Guangzhou and other 14 major cities to delimit the boundaries. There are many cities with the urban space structure expanding like standing pancake so that large area enclosure occupies a large number of high-quality cultivated land. Meanwhile, it is the measure that avoids the blindly excessive urban sprawl and protects cultivated land and ecology.
If we want to control urban sprawl effectively, we need to study determinants that drive the spatial growth of cities. Potential determinants are selected based on extensive literature review from four categories: Economic, social, demographic, and natural. Multivariable linear regression and variances partitioning are employed to identify and compare the determinants of urban sprawl and their relative importance across the 30 metropolitans. Results show that the identified determinants vary with metropolitans but present some similarities. Economic growth, industrial development, and economic structural transformation are the key economic determinants. Population and labor growth, population urbanization, and population structure act as essential demographic determinants. Primary social determinants include infrastructure construction, energy consumption, and real estate development, while dominant natural determinants are the amount and topology of available land
[16].
In literature, most of the works focus on a closely related issue between the effect of transportation subsidies and housing subsidies on urban sprawl. Subsidies can reduce commuting cost and encourage urban sprawl. Many studies proved that transportation subsidies can create urban sprawl
[1,17,18]. Those present that if commuters do not pay the full cost of their travel, they are willing to travel a greater distance and make more frequent trips. In addition, housing is the primary motivation for residents moving to the periphery
[19]. Housing subsidies can reduce the residents' housing cost so that they can afford larger houses. Therefore, larger houses will inevitably need to occupy more land resources and result in intensifying urban sprawl. Brueckner
[18] studied the effect of transportation subsidies on urban sprawl by constructing a single-mode model. Su and DeSalvo
[17] provided an extension of Brueckner's model with a two-mode model to the impact of transportation subsidies on urban sprawl. Based on these, we introduce housing subsidies into our model to analyze the effects both of transportation and housing subsidies on urban sprawl. Here, we present a theoretical analysis of the effects. Moreover, we also study how to maximize the urban-area-wide spatial equilibrium utility level.
2 Subsidies and Urban Sprawl
2.1 Urban Spatial Model
This subsection presents a monocentric urban spatial model with two transportation modes. Here, we assume that a public transit line is parallel to a highway connecting home to workplaces. The total transportation costs can be formulated as follows:
where means public transit, denotes private car, is the fixed cost; is the marginal cost of travel; is the distance from CBD; (), is the subsidized proportion to mode .
We assume that , . Then there exists a point where traveler cost is the same regardless of transportation modes. From Equation (1), we can get . Obviously, public transit has lower fixed cost than private cars but with a higher marginal cost. It means that travelers living closer to CBD choose public transit and travelers living near fringe choose auto.
Total housing cost is given as follows:
where is land consumption; is land rent; is the subsidized proportion of house and , then is the portion of housing cost paid by residents.
A household's quasi-concave utility function is
where is nonland, non-transportation expenditures.
We assume a household subject to the following constraint:
where means the household's exogenous income; is the income tax rate. The problem of the household is to maximize Equation (3) subject to Equation (4). We can get
We assume all urban households' income and utility function are the same. Consequently, there is no household that wants to move so that the urban is in spatial equilibrium.
where is the urban-area-wide spatial equilibrium utility level.
Since at , and the urban boundary conditions can be formulated as follows:
where is city fringe at which the land rent equals to agriculture .
The urban population is
where is the number of radians in a circle available for urban residential use, and is the urban population. Especially, we assume that the urban population is the same as the number of the urban households in the article. The condition ensures the urban population fits the urban boundary.
Since government subsidy is limited, it should be constrained to balance countries' budgets
where the left-hand side is urban-area government revenues devoted to urban-area transportation and residential housing, and the right-hand side is urban-area government expenditures on transportation and residential housing. is the share of urban-area tax revenues for transportation and residential housing, where is the tax share , and is intergovernmental grants devoted to transportation and residential housing. The first term of the right-hand side is the public transit costs paid by the government. The second term of the right-hand side is the auto costs paid by the government. The third term of the right-hand side is the housing costs paid by the government.
2.2 The Effects of Transportation and Housing Subsidies
In Brueckner's original study
[18], the effect of transport subsidies is discussed in a single-model; Su and DeSalvo
[17] extends it into a two-mode model. Here housing subsidies are introduced into our two-mode model to analyze the effects of both transport and housing subsidies on urban sprawl.
To obtain the comparative static effects of these variables on land rent and land consumption, we get the totally differentiate of Equation (6):
Substituting (5) into (11) and rearranging, we get
Then the following effects of change in exogenous variables on can be derived from (12):
According to Hicksian demand slope, , we can get
Brueckner (1987) provides the effect of the spatial utility level on housing consumption, which can be used in our model. So we can obtain
where ensures is a normal good. Using Equations (13)(14), we can get .
To obtain and requires the simultaneous solution of Equations (8) and (9), and the solutions depend on , , , , , , , , , , and . To obtain the effects, we totally can make stand for exogenous variables listed above. Then, we can obtain from Equation (8) and from Equation (9).
Getting the first-order differential of (8) with respect to , we can obtain
Rewrite Equation (9), we get
Totally differentiate Equation (17) with respect to and we can get
where , and terms involving are canceled out because . At the place , we have and .
Substitute Equation (16) into (18), we can obtain
Clearly, , and , the denominator of (19) is negative.
By making stand for exogenous variables, we get some propositions.
Proposition 1 Certeris paribus, urban area expands with the increase in numbers of households, i.e., .
Proof Substitute into Equation (19) and using , we can get
That is proved.
Proposition 2 Certeris paribus, urban area expands with the increase in households' income, i.e., .
Proof Substitute into Equation (19) and using , . Equation (19) can be rewritten as follows:
Clearly, the denominator is negative, then substituting Equations (13)(15) into the numerator, which can be rewritten as follows:
Since , and , then the denominator and numerator are negative, we get .
Proposition 3 Certeris paribus, the urban area shrinks with an increase in the rural land rent, i.e., .
Proof Substitute into Equation (19) and using , which becomes
Since and the denominator of Equation (23) is negative, thus we get .
Proposition 4 Certeris paribus, the urban area shrinks with an increase in the income tax rate, i.e., .
Proof Substitute into Equation (19) and using , the first-order differential can be rewritten as follows:
The sign of the numerator is ambiguous, so we can substitute Equations (13)(15) into the numerator, the numerator can be rewritten as follows:
Since , and , then the denominator and numerator are positive, we get .
Proposition 5 Certeris paribus, intergovernmental grants do not affect urban area, i.e., .
Proof Totally differentiating Equation (10) with respect to , we have
which means that falls sufficiently with an increase in so that tax revenues are completely replaced by intergovernmental grants, and there no changes in other endogenous variables. Therefore, we have .
Proposition 6 Certeris paribus, the urban area expands with an increase in the fixed cost of public transit, i.e., .
Proof Substitute into Equation (19) and using , the first-order differential can be rewritten as follows:
Since , and the denominator of (27) is negative, thus we get .
Proposition 7 Certeris paribus, the urban area expands with an increase in the traveling marginal cost of public transit, i.e., .
Proof Substitute into Equation (19) and using , Equation (19) can be rewritten as follows:
Since , and the denominator of (29) is negative, thus we get .
Proposition 8 Certeris paribus, the urban area shrinks with an increase in the public transit subsidies, i.e., .
Proof Substitute into Equation (19) and using , the first-order differential can be rewritten as follows:
Since , and the denominator of (29) is negative, thus we get .
Proposition 9 Certeris paribus, the urban area shrinks with an increase in the total fixed cost of automobiles, i.e., .
Proof Substitute into Equation (19) and using , the Equation (19) can be rewritten as follows:
Substituting Equations (13)(15) into the numerator, the numerator can be rewritten as follows:
Since , and , then the denominator is negative and the numerator is positive, we get .
Proposition 10 Certeris paribus, the urban area shrinks with an increase in the travelling marginal cost of automobiles, i.e., .
Proof Substitute into Equation (19) and using , Equation (19) can be rewritten as follows:
Substituting Equations (13)(15) into the numerator, the numerator can be rewritten as follows:
Since , and , then the denominator is negative and the numerator is positive, we get .
Proposition 11 Certeris paribus, the urban area expans with an increase in the auto subsidies, i.e., .
Proof Substitute into Equation (19) and using , Equation (19) can be rewritten as follows:
Substituting Equations (13)(15) into the numerator, the numerator can be rewritten as follows:
Since , and , then the denominator and numerator are negative, we get .
Proposition 12 Certeris paribus, the urban area expans with an increase in the housing subsidies, i.e., .
Proof Substitute into Equation (19) and using , which becomes
Substituting Equations (13)–(15) into the numerator, the numerator can be rewritten as follows:
According to Equation (4), we can obtain
and
Since , , , , and . Therefore we have
Clearly, the numerator is negative. Since both of the denominator and the numerator are negative, thus we can obtain .
In summary, we find that public transit subsi
y lea
s to urban shrink while automobile subsi
y has the opposite effect, which accor
s the findings of Brueckner, Su and DeSalvo
[17, 18]. Also, housing subsi
y as the new intro
uced determinant could make the city sprawl.
3 Maximization of Equilibrium Utility Level
In Section 2, we assume that all urban househols are the same with respect to utility function and income and the city therefore can achieve spatial equilibrium. And the previous models and analysis are provided on the premise that is the urban-area-wide spatial equilibrium utility level when maximizing equilibrium utility.
To balance countries' budgets, we have added the constraint Equation (10). Then we can stuy how to maximize the urban-area-wide spatial equilibrium utility level in the constraint condition. We cannot obtain the direct findings, but we derive two conditions contributed to calculation analysis of samples.
Proposition 13 In order to maximize spatial equalization utility, constraint Equations and must be satisfied. Equations and are as follows:
and
Proof Totally differentiating Equation (10), getting
and
If travelers choose to travel by public transit, we can have Equation (45) to maximize spatial equalization utility. Equation (45) is
Totally differentiate Equation (4) with respect to and solve for, getting
Substituting from Equations (13), (14), and (43) into Equation (46), after some manipulation, prouces
And substituting from Equation (47) into Equation (45), which becomes
If travelers choose to travel by automobile, we have Equation (49) to maximize spatial equalization utility. Equation (49) is
Totally differentiate equation (4) with respect to and solve for , getting
Substituting from Equations (13), (14), and (44) into Equation (46), after some manipulation, prouces
And substituting from Equations (14) and (51) into Equation (49), which becomes
To sum up, our results show that we cannot obtain the direct findings but two complex equations. However, we derive two constraint conditions contributed to calculation analysis of samples. Anyway, this paper is only a fundamental exploration in the field of maximization of equilibrium utility level.
4 Conclusion
This article analyzes theoretically effects of transportation subsidies and housing subsidies on urban sprawl in a monocentric urban spatial model. We assume the theoretical model incorporates two transportation modes, and our analysis indicates that the urban area shrinks with an increase in public transit subsidies but expans when automobile subsidies and housing subsidies increase. Moreover, our comparative static analysis prouces that the urban area grows with an increase in housing subsidies. In the meanwhile, we also provide some propositions to indicate that how some relevant exogenous variables influence the spatial size of urban areas, among which these findings could contribute to policies makers to control urban sprawl effectively.
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