抄録
In recent years, local cities in Japan have problems such as the deterioration of the living environment, the increase in CO2 emissions, and the inefficiency of maintenance and management of infrastructure, due to the declining population. One of the solutions for solving such problems is the idea of “compact city”. For designing the compact city, it is necessary to understand population change factors in the city. Consequently, in this research, focusing on Higashihiroshima City in Hiroshima Prefecture, authors aim to understand the population change factors in the all city area and to design the future compact city scenarios.
First, authors investigated the spatial patterns of population change in Higashihiroshima for every five years from 2000 to 2010 using the 500 m meshes data of the census. As a result, it is found that rapid population increase due to housing development occur in urbanization control area. It is thought that the relatively loose regulation of housing development permission in the urbanization control area issued by the local government is the reason why many housing developments are done. Actually, as a result of decision tree analysis on the factors of population change, "distance to elementary school" is extracted as a population increase factor in Higashihiroshima. This factor is one of the items in the housing development permission standard.
Subsequently, the increase potential values and the decrease potential values are calculated for each mesh using the decision tree analysis results of population increase and population decrease, respectively. Then, by adding these values to the present population for every five years, authors estimated the future population distribution as of 2040 which is “BAU scenario”. In addition, as a result of calculating the total of urban facilities costs and CO2 emissions as the evaluation index of the scenario, it is found that the costs and CO2 emissions per person are larger in the outside of urban areas with less population.
Next, in Higashihiroshima, authors made scenarios that are thought to be more efficient than “BAU scenario” as follows:
Development control scenario: A scenario assuming that population in-crease in urbanization control area is disappeared by stopping the development permission standard.
Current trend and compact scenario: A scenario in which population is concentrated into efficient meshes of each evaluation in the BAU scenario.
Development control and compact scenario: A scenario in which population is concentrated into the "meshes within 1.01 km from elementary schools" in addition to efficient meshes in the development control scenario. In these areas, the population increase potential is high from the decision tree analysis results.
As a result of comparative evaluation of each scenario from the viewpoint of evaluation indexes, urban facilities costs and CO2 emissions by concentrating the population are expected to be greatly reduced. In addition, it is also found that even in the "development control scenario", in which the population is not concentrated about 1 billion JPY will be reduced in urban facilities costs in the year as of 2040.
