The Hani Terraces of Yuanyang

A length of wood, about an arm span long, lies across the spot where an irrigation channel splits in two.

It has no hinge, no lid and no lock. Along its top, someone has cut a few notches. One notch might be three fingers wide, the one beside it only one finger wide, and the next narrower still. Water comes down from the mountain and rises until it touches the edge of the wood. Then it spills through each notch into the branches below. A wide notch takes in more water, and a narrow one takes in less. No one turns a valve, and no one stands guard.

The Hani people call it a water-dividing log. Where they can find a good slab of stone, they cut the notches into the stone instead and call it a water-dividing stone. That is all it is. A log with a few notches, set exactly where the water parts.

Yet that log is the brain of a whole mountainside.

The mountainside lies in the Honghe region, in the southeast of Yunnan province in China. The terraces spread across four counties, Honghe, Yuanyang, Lüchun and Jinping. They cover about 70,000 hectares. Thousands of steps are stacked from halfway up the mountains down to the floors of the valleys. The Hani have farmed there for more than 1,300 years.

One stream, hundreds of families, and a dry season. That is the hardest problem on any terraced hillside in the world. If the family at the head of the channel builds its bank just a little higher, the family at the tail end watches its field crack in the sun. The Hani solved that problem with a log.

Nobody cuts the notches to suit himself. A branch that feeds more fields gets a wider notch, and a branch with fewer fields gets a narrower one. It all follows the order for drawing water that the whole area has kept from one generation to the next. So the sharing of water does not rest on anyone's promise. It rests in the shape of the log, for anyone passing by to see.

The person who looks after all this is called the channel keeper. His first job is not dividing the water but clearing the channel. Silt settles, leaves fall, earth slides, and before long the channel clogs. Once it clogs, even the widest notch is useless. He walks the length of the channel and clears it, and only then does he watch over the flow. When two families fall out over water, he is the one who settles it.

His pay comes from the families who use the water, and they pay him in rice. Every family whose fields drink from that channel hands over one bucket of unhusked rice, about three kilograms. Here, fairness is not just good advice. It is a notch cut in advance, a channel scraped clean, and a bucket of rice paid on time.

But the log can only share what it is given. If the channel above runs dry, every notch, wide or narrow, is left with nothing. The real question is where the water comes from.

The answer surprises many people. In this whole terraced area there is not a single reservoir. No pond, no tank, no water store. Yet water never runs short, all year round.

The secret is that the Hani did not just stack up fields. They stacked up the whole mountain, in four layers, and no layer may trade places with another. At the top is the forest. Some way below the forest is the village. Below the village are the terraces, step after step, going down and down. And at the very bottom, on the valley floor, is the river.

Water passes through all four layers in exactly that order. From the forest, it follows the channels to the village, where people and their buffalo and cattle use it first. Only after the village does it go down to the fields, from the highest step to the lowest. Past the last field, it flows into the river. Then the sun comes up, and vapor rises from the valley. The monsoon wind pushes it back up toward the peaks. There it meets the thick forest canopy, gathers into mist, and soaks into the soil. And everything begins again.

The whole mountain is a pump that runs on sunlight and leaves. The forest is the reservoir. It simply does not hold its water in a tank. It holds it in the soil, in the roots and in the mist.

Seen this way, keeping the forest here is no longer a well-meaning plea. It is arithmetic. Strip the forest from the peak, and the channel below runs dry. The water-dividing log is left with nothing to divide. So every village keeps a stand of watershed forest, and a stand of sacred forest that no one may touch. In earlier times, besides the channel keeper, the village also had a forest keeper, chosen by the villagers. The two of them guarded the same thing.

Because the water stays almost all year, the terraces here are more than a place to grow rice. In that shallow water live fish, snails and eels. People also raise ducks there, and they plant soybeans right on the banks between the fields. This area once had as many as 195 rice varieties of its own. Today 48 remain, and the villages still swap seed with one another so that no variety is lost for good.

This way of farming is not new. As far back as the Tang dynasty in China, the Hani were known for their skill at opening fields on steep slopes. Today 82 villages still sit exactly where they belong, between the forest above and the terraces below. Their thatched roofs are rounded like mushrooms.

In 2010, the Food and Agriculture Organization of the United Nations named these terraces one of the world's important agricultural heritage systems. Three years later, a core area of 16,603 hectares was inscribed on the World Heritage List.

Now the story comes closer to Vietnam. The river on the valley floor, where the water ends up after passing down thousands of terrace steps, is the Honghe. Flowing on a little way to the southeast, it enters Vietnam at Lào Cai. From there it goes by a far more familiar name, the Red River. It is the very river that flows through Hanoi.

The Hani do not live only on the far side of the mountains, either. In Vietnam they are called the Hà Nhì, one of the country's 54 ethnic groups. Figures from 2019 put their number in Vietnam at more than 25,000. Most of them live in Điện Biên and Lai Châu. Many live in Lào Cai as well. They build houses with walls of rammed earth. And they farm terraces too. The same ethnic group lives on both sides of a mountain region, and on both sides they know how to shape a slope into steps that hold water.

Vietnam knows terraced rice fields well. There are Mù Cang Chải and Hoàng Su Phì, mountainsides that turn bright gold at the end of the season. They were made by many different ethnic groups, in different mountain areas, but the problem is still the same one. Find water up high, and dig channels to bring it down. Cut the slope into steps, and build banks to hold the water. Then share it out among the families, so that even the family at the tail of the channel has enough to plant.

The log still lies where it has always lain, across the place where the channel splits in two. The water arrives, rises, touches the edge of the wood, and spills through each notch, a share going each way. No quarreling, and no one standing guard. Only the sound of water, and a few notches, wide and narrow, strong enough to keep a whole mountainside living together for more than 1,300 years.