...continued from Part 1

4. Ob-Irtysh is a large basin you may never have heard of

Yet another of the world's most important basins in the Ob-Irtysh basin. It includes the watersheds of both the Ob and Irtysh rivers, hence the compound name, and covers large regions of the Russian Federation, Mongolia, Kazakhstan, and the People's Republic of China.

Of the two main rivers, the Ob is smaller and could be considered, on the grander scheme of things, actually a tributary for the larger Irtysh river. The basin covers an area of roughly 1.14 million square miles, or 3 million square kilometers, and is the foremost drainage basin in Asia. The Irtysh river's primary source lies in the Mongolian Altai in Dzungaria (just north of Xingjiang, PRC), close to the border of Mongolia.

The Ob river is one of the largest rivers in Asia and, when the Irtysh is included, forms the seventh-longest river system in the world. Both the Ob and Irtysh eventually dump their freshwater into the Kara Sea, a subsidiary of the Arctic Ocean, via the Gulf of Ob. This just so happens to be the world's longest estuary too.

With regards to the Ob, the largest city along its course is Novosibirsk, which is the most important city in all of Siberia. It is also the third-largest in Russia. Both the Ob and Irtysh are vitally important sources of freshwater for the region, and also provide very important economic activities including energy generation, agriculture, and freight transport.

Historically, the main rivers of the basin have been contaminated with nuclear waste dumped from Soviet nuclear testing that has, sadly, affected native plants, animals, and humans throughout the region.

5. The Rio de la Plata Basin is another vitally important river basin

Moving over to South America again, another of the world's most important drainage basins is the Rio de la Plata Basin. More commonly known as the River Plate Basin, it covers an area of roughly 1.2 million square miles (3.1 million square kilometers), this watershed gets its name from the main drainage river for the region, the mighty Rio de la Plata ("River of Silver", or "Silver River" in Spanish).

The basin drained by the main tributaries of the Río de la Plata (Uruguay, Paraná, and Paraguay) covers approximately one-fifth of South America. Where the rivers join, they form the widest estuary in the world, which drains into the Atlantic Ocean.

The basin is bounded by the Brazilian highlands to the north and Andes Mountains to the West. The entire system drains into the Atlantic Ocean at a rate between 15 and 26 thousand cubic meters per second.

The entire basin also acts as an important recharge zone of the Guarani Aquifer - one of the largest of its kind in the world. Like the vast majority of major watersheds and basins around the world, its waters are tapped by various human activities including drinking water, agricultural irrigation, power generation, etc.

It stretches over various South American countries including, Bolivia, Brazil, Paraguay, Uruguay, and Argentina. Second, only in size to the Amazon Basin in South America, it covers roughly a quarter of the entire landmass of the continent.

From the conflicts of the Spanish and Portuguese conquests to more modern naval conflicts like the famous "Battle of the River Plate", the region is, sadly, more than familiar with human conflict.

6. The Yenisey Basin is the largest that drains into the Arctic Ocean

The Yenisey, or the Yenisei, is another of the world's largest and most important basins. Situated across the Russian Federation and Mongolia, its main river, the Yenisey, is the largest of the major Siberian rivers.

The basin covers an area of about 965 thousand square miles or 2.5 million square kilometers. The Yenisey rises in northern Mongolia and is fed by several other large tributary rivers like the Angara, Podkamennaya Tunguska, and Nizhnyaya Tunguska. The entire basin, via the Yenisey, drains into the Yenisey Gulf in the Kara Sea.

A major and important feature of the upper part of the Yenisei River Basin is Lake Baikal, considered the deepest and oldest lake in the world.

The waters of the basin include many species of fish, some of which are unique to the region like the gobionine cyprinid and grayling. The region is also home to the Taimyr reindeer herd which is, by all accounts, the largest of its kind in the world.

This herd migrates to winter grazing grounds along the Yenisey every year and is a real sight to behold on the move.

7. The Amur, or Heilong Jiang basin, is home to some of the world's most endangered big cats

Yet another of the world's most important basins is the Amur, or Heilong Jiang, river basin. The former is the Russian name for the river and the latter is modern Chinese for "Black Dragon River".

Stretching across the borders of the People's Republic of China, the Russian Federation, and Mongolia, its main drainage river, the Amur/Heilong is the world's tenth longest river.

This river forms the main boundary between China and Russia, and the entire basin has an area of around 716 thousand square miles or 1.85 million square kilometers.

The basin is home to some interesting endemic lifeforms including, but not limited to, the Kaluga (a large predatory species of sturgeon), northern snakehead, yellow cheek fish, and softshell turtle. The Kaluga can reach lengths in excess of 18 feet (5.6 meters).

The river, by which the watershed derives its name, is historically very important for the region and is an important symbol of Chinese-Russian relations stretching back centuries. For example, it played a role in border conflicts during the Sino-Soviet split between the 1950s and 1960s, when ideological differences led to serious degradation in relations between the two nations.

The basin is also home to some endangered species of big cats like the Amur tiger and Amur leopard. According to the World Wide Fund for Nature (WWF), the incredibly biologically diverse region is under increasing pressure from economic development and illegal wildlife production.

8. The Yangtze river basin is one of the world's biological treasure troves

Famed for its enormous biodiversity, the Yangtze river basin is another of the world's largest and most important basins. Named after the mighty river Yangtze (the world's third longest river, and the longest in Asia), the entire basin covers an area of roughly 700 thousand square miles. To put that into perspective, that is around 4 times the size of California!

The Yangtze rises on the Tibetan plateau, and flows, more or less, due east until it reaches the East China Sea. The entire basin from which it is fed accounts for roughly one-fifth of the entire area of China, and is also home to something like a third of China's entire population.

Due to the river's enormous size and length, the river, and by extension the entire basin, has played a vitally important role in Chinese history and economics for millennia. For thousands of years, the river has been used as a source of potable water, industrial process, military use, and, of course, energy production.

The Three Gorges Dam, for example, is situated on the Yangtze and is the largest hydroelectric dam in the world. Interestingly, the area around where the dam is built has evidence of human habitation as long ago as 27,000 years!

The Yangtze delta, one of the largest in the world, is vitally important for China's economy today, accounting for around 20 percent of its entire gross domestic product (GDP).

9. The Huang He basin is also huge

nd lastly on our list of notable global drainage basins, is the Huang He, or Yellow River, basin. Situated primarily in the People's Republic of China, its main river from which the basin derives its name is the second-longest in China and sixth-longest river in the world.

The basin covers an area of roughly 307 thousand square miles, about 795 thousand kilometers squared, and ultimately drains in the Bohai Sea by the Shandong Province city of Dongying. Waterways within the basin run generally west to east and cross various Chinese provinces including Qinghai, Gansu, Sichuan, Shaanxi, Ningxia, Shanxi, Henan, Shandong, Hebei, and some parts of the autonomous region of Inner Mongolia.

The Yellow River basin is not only fascinating from a geographical point of view but also historically, as it is thought to be the cradle of the ancient Chinese civilization.

The basin, and its rivers, are constantly plagued by floods that can be incredibly devastating. Some have even taken the lives of many millions of local inhabitants, including the 1332-33 flood during the Yuan Dynasty, the 1887 flood during the Qing Dynasty, and the 1931 flood during the Republic of China.

The floods are caused by the large amounts of fine-grained sediment carried by the river from the Loess plateau that constantly deposits itself at the bottom of the Yellow River's bed. It is, in fact, this high sediment content that gives the river its characteristic color and, hence, its name.

Previous flooding events have been so severe that they have changed the course of the river several times from all generally north-easterly, except during the Jin-Yuan and Ming-Qing dynasties between the 12th and 19th centuries when it flowed more due easterly. In more recent times, the threat from devastating flooding has been partially controlled through the construction of dams and better river management.

Why do we need to study watersheds?

We hope, by now, that you've gained some appreciation for the importance of watersheds to human civilization and nature. Without water, there can, quite literally, be no life, so it is crucial that we understand what watersheds are and how to reduce, as far as reasonably practicable, our impact on them.

Watersheds and drainage basins are vital for many foundational parts of modern human society from growing food, industry, drinking water, power generation, sanitation, etc. In fact, studying the health of a watershed is usually a good proxy for assessing how well managed the land of the watershed is.

If the water that flows through it is heavily polluted, for example, it usually indicates some very serious problem with some aspect of the ecosystem upstream. If the water has a high silt content after the rain this may indicate that the soil is eroding somewhere in the water basin that needs attention.

Rivers may contain high levels of chemical pollutants that, obviously, indicate someone, somewhere, is releasing large amounts of them upstream. If the discharge varies a lot in short intervals, then the runoff from the land's surface is probably not well managed and there may be improperly designed developments.

Watersheds in any region can have one, or more, of these issues, and for this reason, among others, it is vitally important for authorities to understand the "hows" and "whys" of watershed issues to better understand the watershed's ecology, or "ecological function". A well monitored and managed (as best humans can manage an enormous natural process) is good for not just human beings, but the ecosystem that supports our civilizations too.

continued in Part 3