On Nov. 30, the Ministry of Internal Affairs and Communications released its calculations of the population in each Lower House single-seat constituency based on the finalized 2020 National Census data. It has been confirmed that five prefectures will see an increase in their number of single-seat constituencies and 10 prefectures will see a decrease of one each. The Liberal Democratic Party holds more than 70% of the seats in the single-seat constituencies in the prefectures that will see their seats decrease. If adjustments cannot be made among the candidates, multiple LDP candidates will end up competing with each other for a Lower House seat.
The “Council for the Demarcation of Constituency Boundaries for Elections to the House of Representatives” will develop a plan for rezoning constituencies so that the maximum vote-value disparity among single-seat constituencies is less than two times. The Council is set to submit a recommendation by next June. The value of a single vote in the Tottori constituency, which has the smallest population according to the 2020 National Census, was 2.096 times greater than that in the Tokyo No. 22 district, which had the largest population.
Tokyo will gain five more single-seat constituencies and Kanagawa two. One constituency each will be added in Saitama, Chiba, and Aichi. Meanwhile, Miyagi, Fukushima, Niigata, Shiga, Wakayama, Okayama, Hiroshima, Yamaguchi, Ehime, and Nagasaki Prefectures will see their constituency number decreased by one.
It is especially difficult to make adjustments in prefectures that have Lower House members who have been elected many times. Yamaguchi Prefecture, where the number of seats allocated will be reduced from four to three, have former Prime Minister Abe Shinzo, Defense Minister Kishi Nobuo, and Foreign Minister Hayashi Yoshimasa currently serving. Shiga and Ehime, where the Liberal Democratic Party holds all the single-constituency seats, as in Yamaguchi Prefecture, will also likely see LDP incumbents competing against each other.
There will also be changes in the number of constituencies allocated to proportional representation blocks. The Southern Kanto block will increase by one from 22 to 23, and the Tokyo block will increase from 17 to 19. In contrast, the Tohoku, Hokuriku-Shin’etsu, and Chugoku blocks will decrease by one each. If no agreement can be reached and elections in which two LDP candidates compete with each other are held, it will give opposition party candidates an advantage.
Enacted in 2016, the legislation related to the reform of the Lower House electoral system stipulates that single-seat constituencies are to be allocated using the Adams’s method based on 2020 National Census data.