The Yangtze River did not always exist. Neither did China. In fact, all of the rivers, mountains, continents, and oceans on the planet today were formed over millions and millions of years. In this section, we will learn how the Yangtze was “born” by studying China’s geology and climate.

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• Part 1: The Birth of the Yangtze
• Part 2: River Fluctuations
• Part 3: Why Does the Monsoon Switch Directions?
• Part 4: Monsoon Quiz

How was the Yangtze “born”? To help answer this question, let’s do a quick thought experiment.

Imagine you wanted to create a new river. What two things would you need? First, obviously, you would need water to supply your river. Without water, there would be no river. Second, you would need an area of land where your river could flow, and this land should be sloped and uneven (e.g., with mountains and valleys) so your river has a clear downward path. If your land were completely flat, your water would have nowhere to flow and would never form into a river.

To understand how the Yangtze was “born,” therefore, we need to examine two things: how the Yangtze gets its water, and how China’s terrain became so uneven.

Let’s start with China’s land. Today, China’s terrain is filled with mountains and valleys, especially in China’s south and west, its areas closest to India. In fact, the region where China and India converge is the most mountainous place on the planet, home to the Himalayas and all 100 of the world’s tallest mountain peaks! It is also home to the Tibetan Plateau, where the Yangtze River originates. Spanning about four times the area of France and standing at more than 4,500 meters (14,800 feet) above sea level, the Tibetan Plateau is both the largest and highest plateau in the world.

This area was not always so mountainous, however. Seventy million years ago, this region was not just flat — it was underwater! At that time, the area of land we now call India was its own continent, separated from the rest of Asia by an ocean. (See the time-lapse illustrations below.) Since then, India has drifted northward a few centimeters per year, finally colliding with Asia like the slowest, most massive car crash in the world. This gradual drifting of India into Asia is part of a geological phenomenon called “plate tectonics.”

When India collided into Asia, it caused vast amounts of land to shift, uplift, and crumple — much like a car crash can cause the hood of a car to shift, uplift, and crumple. This violent collision of the continents dramatically transformed the land, and over millions of years created the giant Tibetan Plateau, the Himalayas, and several other mountain ranges. In fact, India has still not finished its northward drift; it continues to slowly crash into the rest of Asia today, raising the surrounding land a few centimeters higher each year and causing numerous earthquakes, often with disastrous consequences.

Because of its great elevation, the Tibetan Plateau is an ideal place for large, powerful rivers to originate. The Yangtze and many of Asia’s other major rivers begin in this area. China’s southwestern highlands provide these rivers with a lofty starting point and a dramatic slope down which they can flow to the sea. For the Yangtze, the landscape provides a clear west-to-east path. For rivers, this path is called a “course.”

Now that we understand how the Yangtze got its course, let’s learn how the Yangtze gets its water.

Like most rivers, the Yangtze gets a lot of its water from precipitation. When rain falls on land, gravity naturally pulls the rainwater downhill and collects it into larger and larger streams of water. Small streams merge to form large streams, large streams merge to form small rivers, and so on. Eventually, all the area’s streams and rivers flow into a main river, like the Yangtze. These smaller streams and rivers are called “tributaries,” and the whole network of rivers is called a “river system.”

The process of rainwater trickling downhill, collecting into a river system, and eventually flowing away to sea is called “drainage,” and the area of land that a river system drains is called a “drainage basin” or “watershed.” Major rivers often have very large drainage basins. For example, the Yangtze’s basin covers about one-fifth of China’s total land area. Any raindrop that falls in this area eventually makes its way to the Yangtze River. The illustration below shows the Yangtze river system and drainage basin.

Although rain supplies much of the Yangtze’s water, the Yangtze also has another major water source: ice melt. In the western highlands of the Tibetan Plateau, near the river’s origin, much of the Yangtze’s water comes from melting snowpacks and glaciers. The Tibetan Plateau is the world’s third-largest store of ice, behind the Arctic and Antarctic, and when these enormous Tibetan glaciers and snowpacks melt, their waters flow into river systems like the Yangtze.

Like other rivers, the Yangtze’s water level fluctuates. These seasonal fluctuations are predictable: the Yangtze’s water level rises in the summer and recedes in the winter. During some summers, if the water level rises too high, the river may even breach its riverbank and flood nearby farmland, villages, towns, and cities. Floods like this often have a heavy toll, including loss of land, property, and even lives.

What causes the Yangtze’s predictable seasonal fluctuation? There are two main reasons.

First, the ice and glaciers near the river’s source melt quickly during the warm summer months, supplying the Yangtze with more water and raising its water level. These glaciers do not melt as quickly (or do not melt at all) during other times of the year.

Second, China experiences significantly more rainfall in the summer than in the winter. The summer’s heavy rains contribute even more water to the river, while the winter’s dry months cause the river’s water level to recede. This rain pattern is due to China’s “monsoon climate.”

Different regions around the world have different types of climates, and each climate is characterized by many factors, such as temperature, wind, and precipitation. For China (and many of its neighboring countries), climate is strongly determined by a special kind of wind called a monsoon.

Most winds blow reliably in the same direction year-round. The monsoon wind, however, blows in different directions at different times of the year. During China’s summer months, the monsoon winds blow from sea to land, bringing humid air to China. This moisture-laden air leads to China’s reliable summer rains. In the winter, however, the monsoon winds switch direction and blow from land to sea. As the air over China blows out to sea, it is replaced with cold, dry air from China’s north and west (Siberia and Inner Asia). Because this air from Siberia and Inner Asia contains very little moisture, winter rains are relatively rare in China.

To understand why China’s summer winds blow opposite to its winter winds, we must first understand three principles:

1. Warm air expands, creating a low-pressure system. Cold air is dense, creating a high-pressure system.
2. Air always moves from high-pressure systems to low-pressure systems. This movement of air is what we call “wind.”
3. The temperature of land can change quickly and greatly, but the temperature of water changes slowly and only moderately.

Let’s look at each principle one at a time. Once we understand the three principles, we will put them together to explain why the monsoon winds change. Air is composed of molecules. When air is heated, these molecules try to spread themselves further and further apart from each other. We say that the air “expands” and creates a “low-pressure system.” Because these hot air molecules are so far apart from each other, it is easy for other nearby molecules to enter the area.

Conversely, when air is cooled, air molecules tend to huddle closer and closer together, making the air “dense” and creating a “high-pressure system.” Because these cold air molecules are huddled together so closely, it is difficult for other nearby molecules to enter the area.

Whenever possible, air molecules try to space themselves evenly from each other. Because of this, air always moves from high-pressure systems (i.e., areas with dense molecules) to low-pressure systems (i.e., areas with sparse molecules). In other words, wind always blows away from high-pressure systems and toward low-pressure systems. Land consists of many different types of material — rock, soil, sand, etc. Each of these has its own properties, but as a whole, these materials change temperature quickly when they are heated or cooled. For example, if you took the temperature of the dirt or pavement in front of your home in the middle of the day (after heating in the sun for several hours) and the middle of the night (after cooling for several hours), you would get two significantly different numbers.

Water is very different. If you took the temperature of a sea or ocean in the middle of the day and the middle of the night, your two temperature readings would be very similar to each other. This is because water changes its temperature slowly when it is heated or cooled. Because of this, the sea temperature does not change much over the course of a day.

This same pattern holds true over the course of a year. As the seasons change from summer to winter, land temperatures fluctuate more quickly and dramatically than sea temperatures. In summer, the land becomes hotter than the sea; in winter, the land becomes colder than the sea. This feature is essential for understanding the monsoon wind.

First let’s consider what happens during the summer. In the summer, land temperatures become higher than sea temperatures. Because of this, the air that sits above the land — which we can call “continental air” — becomes hotter than the air that sits above the sea (or “maritime air”). The heated continental air expands and creates a low-pressure system. Finally, because air always moves from higher-pressure areas to lower-pressure areas, wind blows toward land from the sea. Thus, we can explain why the monsoon blows from sea to land in the summertime.

The exact opposite process occurs in the winter. Because land temperatures fluctuate more dramatically than sea temperatures, the land now becomes colder than the sea. The cooled continental air becomes dense and therefore creates a high-pressure system over land. Thus, air now moves away from the continent, producing the monsoon’s winter winds, which blow from land to sea.

As you can see, when we apply these three principles together, we can explain why the monsoon switches directions from summer to winter. Congratulations! You now understand the monsoon!

Want to review what you just learned? Double-check your understanding by taking the monsoon quiz.

China is a vast country with a far-flung population and large areas of inhospitable terrain. As a result, harnessing and distributing water are key elements in the political and emotional history of the nation. This is especially true for people who live along the Yangtze, where floods and droughts are a constant part of life. Records show that from the second century BCE to the present, the Yangtze averaged a major flood every ten years and a catastrophic flood every hundred. For example, between the beginning of the Han dynasty in 206 BCE and the end of the Qing dynasty in 1911, 214 major floods were recorded along the Yangtze. The greatest destruction was usually in the middle reaches where the land is flat and heavily settled.

During the 20th century, China saw an almost record number of floods. In addition to geographical and climate issues, over-cultivation of the riverbanks as the population increased and destruction of forests and misuse of land during the Great Leap Forward and the Cultural Revolution exacerbated the flooding.

In 1931, a catastrophic flood affected an area of 8.4 million acres (an area approximately the size of New York state), submerged 7.4 million acres of farmland, destroyed 1.8 million houses, and caused the deaths of 145,000 people. Only four years later in 1935, another 142,000 people perished when 3.74 million acres were flooded again.

In 1954, serious floods once again swept across central China. Due to water conservancy measures taken by the Beijing government, however, Wuhan (made up of the three cities of Hankou, Wuchang, and Hanyang) was spared the awful flooding that occurred in 1931. Its salvation, however, was achieved in part by opening upstream dikes so that water was diverted to heavily populated farm lands to the north. In 1991, much of the same area was once again inundated by widespread flooding. As in 1931, relief efforts were energetic but of only limited effectiveness. Once again nature demonstrated its power to overwhelm man’s best efforts. In 1998, the Yangtze flooded once again, resulting in 3,656 deaths, the destruction of 5.7 million homes and damage to seven million more. In addition, 14 million people were forced to move to new areas.

Throughout time, Chinese leaders hoped that a great dam could not only relieve the suffering and destruction caused by the uncontrollable summer waters, but also provide power for widespread economic development. Currently, China hosts more than 87,000 dams, including nearly half of the world’s 50,000 large dams (three times more than the United States), and construction continues. A cascade of 20 major dams already harnesses the Yellow River, and another 18 are scheduled to be built by 2030.

At the end of 1994, construction began on the Three Gorges Dam, one of the world’s largest hydropower projects. It was completed on the Yangtze River in 2009. Intended both to prevent flood disasters downstream and to generate electricity equal to 15 power plants, this Herculean project cost more than $25 billion to build; forced more than 150 million people (almost half the population of the United States) to relocate; and submerged farmland, cities, and towns, as well as some of China’s most revered scenery and ancient artifacts.

Without a doubt, flood control was the number one motive for building the Three Gorges Dam. Many critics of the dam seem not to consider flood control as a serious issue — and emphasize the motives of hydropower and money-making corruption as the real motives for the creation of the dam. While it is true that over half the expenditures on the dam were devoted to relocation, and this was where, unfortunately, much corruption took place, the fact that floods had displaced and destroyed far more people and property is indisputable.

Of course, no amount of human action can completely eliminate the danger and destruction of floods — in China, the United States, or elsewhere. The history of the Three Gorges Project is still quite short, but since the dam’s construction, there have been no large floods of the same destructive magnitude as the famous floods of 1931, 1954, or the 1990s. As with other preventative measures, it is difficult to say positively what would have happened if the dam had not been constructed.

Crucial to an understanding of China’s water supply are its population and its geography. More than 1.3 billion people, or one-fifth of the world’s population, live on a fraction of China’s land. (China’s landmass approximates that of the United States, but more than a third of it is too high, too cold, or too dry to be habitable.) Although China holds 20 percent of the world’s population, it has less than 10 percent of the world’s arable land, and 7 percent of its available freshwater. The World Bank estimates that China possesses only one-fourth of the global average of water per capita and that by 2030, the per capita supply will have fallen to a level that meets its definition of a water-scarce country.

As a result of scarcity and pollution, China is draining its groundwater and aquifers to such an extent that the World Bank warns of “catastrophic consequences for future generations.” Today, two-thirds of China’s total water consumption comes from aquifers, and the water table keeps falling. In the North China Plain, 44 percent of shallow groundwater is polluted, and little more than 20 percent can be drunk without treatment. Some experts argue that at the current rate of extraction, the aquifers beneath the plain will be depleted in 30 to 40 years.

In northern China, nearly half of China’s population lives in this arid landscape, which contains only 15 percent of the country’s water. This region also generates more than 25 percent of China’s total gross domestic product (GDP) and produces much of its grain. Of the approximately 660 cities in China, more than 400 lack sufficient water. This includes more than a dozen cities with populations greater than two million — including Beijing, the capital city in the north, at around 20 million. Moreover, China’s vast countryside — and its 738 million peasants, more than twice the population of the United States — bears the brunt of this shortage.

In contrast to China’s north, most of the country’s precipitation and groundwater are concentrated in the south, where the population density and industrial production are significantly lower. This geographic mismatch in population, production, and water is a significant factor in China’s water challenges.

To address the increasingly serious water situation in the north, China’s government has tried to solve challenges with massive engineering projects. Launched in 2002, China’s $65 billion South-to-North Water Transfer Project is the largest construction project in human history. The construction will move vast quantities of water from the southern Yangtze River to the water-hungry north through a series of grand aqueducts — an eastern, central, and western route, carved through mountains and etched across deserts, diverting water hundreds of miles.

Although the first phase of the project, finished in 2013, is scheduled to begin water delivery to Beijing, many argue that the subsequent stretches appear geologically, structurally, and financially unsound. The pending western route, which starts in the Tibetan Plateau, is by far the most complex and controversial. Socially, nearly 350,000 people whose homes block construction of this massive project have been forced to relocate, leaving their communities and livelihoods. Ecologically, many experts question whether already-degraded rivers can spare the water, whether silt will compromise the project, and whether fragile and unique ecosystems will be irreparably damaged. In the short-term, this project represents a path of growth that supports the economic development and political stability that is essential for the survival of China’s population and legitimacy of its current government. In the long-term, there is a question whether this project will prove environmentally sustainable.

Water is essential for all life and human survival. It is necessary for all aspects of our lives including food production and security, domestic activities and sanitation, health, energy, industry, and environmental sustainability. Of all the water on Earth, only about 2.5 percent is freshwater. Rivers are the principal systems by which freshwater is delivered to all of us around the world, yet we are imperiling this precious resource in all sorts of ways.

With the silt they carry and deposit over many eons, rivers have turned valleys and their wider basins into rich farmland upon which many societies depend to sustain their populations, as well as to supply the water necessary for agricultural production. The Nile River is but one example among many. Without it, ancient and modern Egypt would simply not exist.

Nor is this all. Large and medium-sized rivers have always been major arteries for the transportation of goods, for the migration of populations, and for the movement of cultures and languages these migrants bring with them. Indeed, before the development of overland transport in the last couple of centuries — railways and highways — rivers and canals were virtually the only way heavy cargoes could be moved. Still today, river shipping is essential to the economy of many countries, including our own. And where rivers flow into the sea, some of the greatest cities of the world are located: the Thames (London), the Hudson (New York), the Yangtze (Shanghai).

Finally, in this brief sketch, rivers are sources of power and energy. Once water’s powerful flow turned machinery directly and early mills and factories were located where falls or rapids could be harnessed. Now, of course, that flow powers turbines that generate electricity — a major source of clean, renewable energy, but where the necessary dams and infrastructure impose heavy environmental costs and sometimes force the relocation of whole populations.

China will soon have the largest economy in the world, currently has the largest population in the world, and also emits the greatest amount of greenhouse gases into the atmosphere. Because of its unique geographical and climatic circumstances, China also has the largest potential for hydroelectric power generation of any country in the world. Therefore, China’s water challenges and its relationship with its rivers are highly relevant to the world at large.

Mountains, rivers, and other geographical realities divide China roughly into eight large regions. Each of these regions is oriented toward a regional “core” more heavily populated, more prosperous, and more developed in general than the areas around it. In most regions, the cores are related to river systems. The rivers bring abundant and dependable water for irrigation and other human uses, though floods may threaten and sometimes devastate. These river systems were also major migration routes along which the Chinese people spread and in whose valleys they settled. It is thus no accident that China’s largest cities have always been located in the regional cores, mostly near important rivers — as in the case in many other societies.

China’s 6,418 kilometer-long Yangtze River is unlike any other great river in the world. Only the Nile and the Amazon are longer and its water volume is in the top five. Originating in the Tibetan Plateau and terminating where it spills out in the East China Sea, the Yangtze both divides and connects the country. The Yangtze River watershed touches 19 provinces and is central to the economic life of more people than the populations of Russia and the United States combined. Studying the Yangtze serves not only as a window into China’s geography, ecology, economy, culture and history, but also its future.