Mobara-shi

In the latest Population Census the population is about 87,000 (86,782 in 2020). This city did not go through the Heisei merger but walked alone, so its recent population trend has no step from a merger. From 93,779 in 2000, holding around ninety thousand through 93,260 in 2005 and 93,015 in 2010, it then turned gently to decline — 89,688 in 2015 and 86,782 in 2020.

Looking inside, the figure of a plain city where gas wells up from below the ground appears. The share aged 65 and over rose from 16.6% in 2000 to 33.2% in 2020, up about seventeen points over twenty years, past three in ten. The household-with-children share is 17.6% in 2020, and the Childcare Waitlist was zero in both 2024 and 2025. The Fiscal Capacity Index was 0.75 in fiscal 2023, a level above the middle, covering three-quarters of expenditure with its own tax revenue. The population gently declining from around ninety thousand, the aging past three in ten, the finances above the middle. Because it walked alone without a merger, this curve has no step, and the town’s real state shows just as it is. Why the finances alone hold their ground ahead of the thinning population — the answer lies not in the Kujukuri plain itself, but in what sleeps below its ground.

This town’s skeleton is set by the landform of the Kujukuri plain, by the natural gas welling up from below its ground, the iodine dissolved in the water, and the bustle of the highway and the temple town. The opening layer is the gas of the deep ground. From below the ground of this land, opening at the southern end of the Kazusa Kujukuri Plain, a burning gas wells up. This land is the foremost producing region in Japan of dissolved-in-water natural gas, centered on Chiba Prefecture, and in its underground brine a certain element is dissolved at twice the thousandfold concentration of seawater. This gas and element welling up from below the ground pushed the modern livelihoods of this town forward.

Along with this natural gas, the iodine dissolved in water put this land on the map of the world. The element taken from the underground brine goes out into the world from this land as one of the foremost producing regions on earth. An old bustle, too, mirrors this town. This land was a strategic point of highway transport and commerce from of old, and it flourished as the temple town of an old temple of the Nichiren sect founded in the Kamakura period; in summer a Tanabata festival among the largest in the Kanto region is held. The Kujukuri plain, the natural gas welling up from below the ground, the iodine dissolved in water, and the bustle of the highway and the temple town — this town’s form stands upon the history of the underground resources that the Kujukuri plain, where gas wells up from below the ground, has held.

What characterizes Mobara-shi is that, while bearing the history of a land where gas wells up from below the ground, it walked alone without the Heisei merger and holds its population near ninety thousand, having turned to decline. After holding around ninety thousand from 93,779 in 2000 to 93,015 in 2010, it fell to 86,782 in 2020, with about seven thousand lost over twenty years. Even in this land that produces the most natural gas and iodine in Japan, part of the younger generation can be read as having moved toward larger cities or toward Tokyo, raising the age of the town as a whole. That the share aged 65 and over reached 33.2% in 2020, past three in ten, is its expression.

On the other hand, the Childcare Waitlist was zero in both 2024 and 2025, and the household-with-children share is 17.6% in 2020. A Fiscal Capacity Index of 0.75 is a level that covers three-quarters of expenditure with its own tax revenue, above the middle. The establishments handling the natural gas and iodine welling up from below the ground, and the manufacturing livelihoods sited on the plain, can be read as supporting the tax source above the middle. The population gently declining, the aging past three in ten, the fiscal stamina above the middle. While the resources below the ground support livelihoods and give thickness to the tax source, the outflow of the younger generation pushes up the town’s age — two forces work in opposite directions on the same plain.

Mobara, as a town opened on the Kujukuri plain where gas wells up from below the ground, holds several functions of its own. One is its history as a land where gas wells up from below the ground — opening at the southern end of the Kazusa Kujukuri Plain, producing the most natural gas in Japan from below its ground, and taking out, on a scale among the foremost in the world, an element dissolved in its underground water at twice the thousandfold concentration of seawater. Another is its character of having flourished as a strategic point of highway transport and commerce, and as the temple town of an old temple of the Nichiren sect, where a Tanabata festival among the largest in the Kanto region is held.

Mobara is a town where the Kujukuri plain became a land of gas welling up from below the ground. From the natural gas and iodine welling up from below, to the bustle of the highway and the temple town, and on to walking alone — the geography of “the southern end of the Kazusa Kujukuri Plain” has stored underground resources and called in the bustle of the highway and the temple town. Below the ground of the flat Kujukuri lie a burning gas and an element dissolved at twice the thousandfold concentration of seawater. More than the bustle on the surface, the richness of the resources stored below has pushed up this town’s modern livelihoods from deep in the ground.