by Ling Zhang
This process still continues today. Between 1855 and 1953, before the People's Republic of China was established to carry out enormous hydraulic works, the river's estuary extended 2 kilometers toward the ocean annually, creating 23.6 square kilometers of new land every year.1 This unstoppable process over the past hundred thousand years makes the Yellow River one of the geological builders of the land of north China. It is fair for those in north China to call the Yellow River their mother river, similar to the way the Egyptians think of the Nile River and the Indians the Ganges. The Yellow River brought the land of north China, including Hebei – a northeastern part of the river's alluvial plain – into being, long before the first human being appeared to make use of its water and to cultivate the land it produced.
Ironically, as much as the Yellow River is widely acclaimed to be the cradle of China and the Chinese, it also has a notorious reputation as “China's Sorrow.” This nurturing mother also shows an unpredictable face of rage and punishment. In historical times, she wielded her power and raised torrential floods again and again, devouring massive amounts of land and people. Historians have found that the river changed the course of its 700-kilometer-long lower reaches at least twenty-five times. Six of these events took place on an extraordinary scale: (1) the river shifted into southern Hebei in the seventh century BCE; (2) into southern Hebei again in the second century BCE; (3) out of Hebei and into northern Henan in the first century CE; (4) into central Hebei between 1048 and 1128; (5) south toward southern China in 1128; and (6) northward between Hebei and Henan-Shandong in 1855.2
Illustration 2. Historical Shifts of the Yellow River's Courses
These major shifts created multiple courses to the river's lower reaches. The separate courses infiltrated the vast space in the eastern part of the North China Plain and stretched out in different directions. Geographically, these courses were grouped into three clusters: northern courses, eastern courses, and southern courses, referring respectively to those within the Hebei Plain, those flowing through northern Henan and Shandong, and those tending toward the south to converge with the Huai River drainage area. These courses swept clockwise and anti-clockwise and moved the river estuary back and forth between latitudes 39° and 32° north. All together they have formed a vast alluvial fan of the Yellow River over 250,000 square kilometers.
This enormous area is the river's floodplain, where it breached its banks along multiple courses to cause tremendous floods. Historians have identified 1,590 flooding events in the past 2,540 years.3 No single historical period was completely free of the Yellow River's floods. From the statistics, we may observe a growing curve in the frequency of flooding events, increasing from once every thirty years before the fourth century, to once every ten years between the fourth and the mid-tenth century, to almost once every year in the Northern Song period, and to twice a year from the late thirteenth century onwards.4 The Northern Song period from the mid-tenth century through the early twelfth century saw a height of river disasters. The environmental drama of 1048, when the river crashed into Hebei and created a cluster of northern courses, occurred right in the middle of these terrible events.
Situating our environmental drama within the long-term trend of the Yellow River's changes makes us wonder how the hands of nature and other environmental forces had collaborated, little by little, to lead the river toward its chaotic condition in the eleventh century. There were two major forces at work: unique hydrological dynamics that caused the river to be flood prone; and historical environmental degradation of the Loess Plateau in the river's middle reaches, which produced and then reinforced the river's hydrological characteristics.
In the past century, dozens of chronicles of Yellow River floods have been compiled in Chinese.5 In nearly all of them, within the opening few pages, the authors employ three phrases to characterize the river: “prone to siltation, prone to overflow, and prone to course shifts” (shanyu shanjue shanxi 善淤善決善徙). This narrative establishes a causal relationship: because the river contains high silt levels and tends toward sedimentation, it is thereby prone to overflow, breach its banks, and shift its course. This causality suggests that it is the river's own hydrological characteristics – in particular its heavy silt and rapid siltation – that have caused various river disasters. To understand where the silt came from and how it led to the exacerbation of the river's situation over a millennium before 1048, we must journey upstream to take a close look at the river's middle reaches, where soil erosion delivered a massive volume of mud, sand, and rocks into the river.
The middle reaches of the Yellow River wind through the northern edge of the Loess Plateau, the world's largest, deepest loess deposit, which is nearly the size of modern-day France. Today, this area supplies 90 percent of the silt that feeds into the Yellow River. The raw material of this silt consists of fine, loose, porous grains of loess. Given extremely low natural precipitation in this area, loess suffers from serious aridity as its porous texture interferes with the retention of moisture.6 Environmental conditions appear even worse as we travel further north to the Ordos area, on the northern edge of the plateau. There, the landscape features extensive deserts and sandy groves, among which the Maowusu 毛烏素 and Kubuqi 庫布齊 deserts being the most famous and well studied. This area is sparsely dotted with drought-resistant grass, small lakes of high salinity, and little patches of oases. Its surface is largely covered by coarse sand.
The texture of the earth, climatic aridity, and the shortage of water all make the Loess Plateau ecologically fragile. The land has a limited capacity to support even thin vegetation and carries little environmental resilience. The vegetation cover – trees, bushes, and grass – does not readily return once gone. Trees, crops, and grazing land for livestock are all difficult to sustain. The latter two form the major human activities that have destroyed this area's natural vegetation in historical and present times. Today, a considerable part of the Loess Plateau appears completely barren year-round. Without a heavy cover of vegetation to shield the land surface, and without the roots of plants to anchor the soil, the fine, lightweight loess is exposed to the open air and can easily be carried away by wind or water.
Illustration 3. The Middle Reaches of the Yellow River
The Yellow River courses around the Loess Plateau and the Ordos area, forming a “Great Bend.” Along its journey, it picks up loess, fine sand, coarse sand, and rocky debris. It is also joined by multiple tributaries that cut through the loess, producing a distinct geomorphology of thousands of tall, earthy masses. Large or small, each of these masses presents a flat, barren top surface and steep cliff-like facets, and each is separated from its neighbors by deep gullies. For millions of years, these local rivers have gushed through the gullies and eroded away the earth, becoming even more loaded with silt than the Yellow River itself. The Wuding 無定 River's silt load, for instance, is 4.9 times that of the Yellow River's, and an even smaller tributary, the Kuye 窟野, has 6.4 times the Yellow's silt load.7 These local rivers stretch deep into every corner of the Loess Plateau to collect silt and then discharge it into the Yellow River.
By the time it finishes circling the Loess Plateau and turns eastward to its low-lying flood plain, the Yellow River has collected 1.6 billion tons of silt – the river's mean silt load per annum in the past few decades. This is seven times the amount of annual sediment discharged by the Mississippi River in the early 1980s and nineteen times the amount of sediment fed into the Colorado River at the Grand Canyon gate from 1948 to 1960.8 In comparison with the North American “Big Muddy,” the Yellow River is no doubt a “Super Muddy.” Its muddy nature determines its hydrological dynamics, as silt blocks up the channel and forces the water to overflow.
Historically, the Yellow River was not always muddy, and the source of its muddy contents, the Loess Plateau, was not always a desolate, denuded land. Behind the river's rapid siltation is a long-term deterioration of the environmental conditions on the Loess Plateau. The dry, barren
image of this area did not manifest in historical literature until the ninth century. It took more than two millennia for the Plateau to develop the unpleasant environmental conditions similar to what we witness today.9
Three thousand years ago, the Loess Plateau seems to have been rather humid.10 The average temperature might have been 2°C higher than today. Under the cover of bushes and broad-leaf trees, animals lived comfortable lives. Tigers, elephants, and rhinoceros that appear in tropical areas today seem to have existed widely in this part of north China. Before sedentary agriculture began, the rich vegetation (both forests and grasslands) sustained in a relatively warm and humid climate and guarded the loess and held it in place. Soil erosion had not yet significantly affected the Yellow River. The river's water ran clear, and it was simply called the “River” or the “Great River” in early Chinese sources.
The mass migration of agricultural population and the colonization of the land gradually transformed this ecologically sensitive zone. Han Chinese began to settle in the region when the Qin 秦 (221–202 BCE) and Han 漢 (202 BCE–220 CE) dynasties competed with nomads for land and sought to incorporate this borderland area into their empires. The first emperor of the Qin 秦始皇 sent 300,000 men to this region to “attack the hu (non-Han peoples).”11 Along with the military actions there arrived an enormous number of corvée laborers, who built and repaired the Great Wall. These men were the first wave of Han Chinese settlers to the Ordos area. During the next three centuries, continuous battles between the Han and the Huns and their struggles for the Great Bend area brought a sizable military population to the area. In 119 BCE, for instance, Emperor Wu of the Western Han 漢武帝 sent 725,000 people from the eastern part of the North China Plain to the Great Bend of the Yellow River to boost agricultural colonization.12
Han Chinese farmers brought a sedentary lifestyle and an agricultural economy to the area. The material provision agriculture provided in turn supported a stable growth in human reproduction. Unfortunately, the gradual increase in human inhabitants and the way they dealt with the surrounding environment led to irreversible negative environmental effects.13 In comparison with nomadic animal husbandry, agricultural cultivation cleared the land more thoroughly; the steady population growth also required the plowing of more and more land, causing forests and grasslands to disappear. Stripped of its vegetation, the once-moist earth became dry and the porous soil began to travel. As a result, the siltation of the Yellow River accelerated and clogged the river's lower reaches. Between the mid-second century BCE and the first century CE, the river produced serious floods, and the river itself became known as the “Yellow” river.
After the first century, the environmental situation seems to have improved temporarily. The fall of strong imperial powers in northern China might have put a pause to the mass migration into the area. The return of nomads possibly drove some Han farmers out, replacing farming with a mixture of both farming and animal husbandry. It is likely that the land was given enough time for its natural vegetation to recover, leading to a reduction of soil erosion and corresponding silt in the river.
For a while, the environmental conditions on the Loess Plateau appeared favorable. In 407, Helian Bobo 賀連勃勃, a chieftain of the Huns, established the Xia 夏 Kingdom and built his capital, Tongwan Cheng (統萬城, lit., City to Rule the Myriad), in middle of the Ordos. Today, this part of the Ordos is covered by sand and is known as the Maowusu desert, but in Helian's time the land was verdant with natural streams and lush grasses. As Helian remarked, “I have traveled to many places, but none of them are as beautiful as here.” Archaeological works also suggest that the earth stratum associated with that historical period consisted of dark, moist, and quite fertile soil. Helian resettled 400,000 Han Chinese slaves there to engage in agricultural production for his state.14 It seems that for the founder of the Xia Kingdom, the northern part of the Loess Plateau was rich enough in natural resources to support all sorts of economic activities that sustained his myriad subjects as well as his military. This suggests that in the fifth century environmental conditions must have been rather benign; large-scale deserts had not yet come into being.
It is very likely that the resettlement and re-colonization of the land by farmers – introduced by Helian as well as rulers and warlords over the next several centuries who had to rely on the Loess Plateau as their production base – once again exposed this area to the same environmental destruction it experienced centuries before. The establishment of centralized empires in the Sui 隋 (598–617) and Tang 唐 (618–907) dynasties once again turned the northern Loess Plateau into the Chinese northern frontier. The old strategy of the Qin and the Han to stuff the land with Han migrants was used again. The land within the river's Great Bend was filled with state-sponsored military colonies, Han Chinese farmers, and non-Han groups that adopted a sedentary lifestyle.15
The revival of agriculture and the population boom challenged the environmental capacity of the Loess Plateau. By the mid-ninth century, excessive cultivation had depleted the vegetation and nutrients in the soil; temporary settlers migrated from one place to another to search for new land, leaving desolated earth in their wake. Helian Bobo's Tongwan City had been seriously eroded by sand and wind. In 822, a sandstorm could easily toss up sand dunes as high as the city walls. Several decades later, travelers who came in search of the past splendor would only find a pile of remnants in a vast stretch of yellow sand. By the end of the Tang period, soil erosion became so serious that the Yellow River's tributaries were heavily silted and blocked up. The Wuding River flooded and shifted its course many times and eventually acquired its name as the “Unsettled River.” The Wei 渭 River in the southern Loess Plateau ran through the suburb of the Tang capital, Chang'an 長安. It was so silted that, starting in the late eighth century, its water overflowed frequently and put the capital city in great danger.16
After the first century, the Yellow River was rarely reported to flood. Sadly, this eight-century-long state of tranquility, “anliu 安流 (lit., peaceful flow)” as Chinese historical geographers call it, was to end in the Tang period. At first, the river's middle reaches on the Loess Plateau became so unstable that the river often meandered from its mainstream. Military towns and garrisons originally considered to be “inside the river” became “outside the river,” or vice versa, not because these settlements were relocated or the districts had been displaced, but because the river's course had shifted.17 As the decades passed, the impact of soil erosion slowly extended eastward to the river's lower reaches. A few small-scale floods were observed by people living downstream in the ninth century. These minor events would develop into serious floods that took place nearly once every four years in the tenth century.
As the tenth century approached, the climate showed a drier tendency, and this played a significant role in the worsening of environmental conditions in north China. Statistics of disaster records in the tenth and eleventh centuries show that drought frequently affected the Loess Plateau.18 This increasing aridity would have harmed vegetation, depleted the earth's moisture, and accelerated the desertification of the land. As a result, more sandy material entered the river. Reports of sandstorms (yutu 雨土, lit. earth storms) increased greatly in the eleventh century.19 Although most of the sandstorms affected the lower Yellow River valley and were witnessed by people there, the sandy materials that produced such storms came from a place nearly a thousand kilometers away, namely the Loess Plateau.20
The dual impact of human activities and the climatic tendency together modified the environmental conditions in the Yellow River's middle reaches. Within this broad temporal and spatial context, the making of the environmental drama in 1048 had come about as a result of profound interregional environmental and geological exchanges.
A Thousand Years of Tranquility
As the Loess Plateau continued to feed the river tremendous amounts of silt from a thousand kilometers upstream, the failure of the downstream flow to process and d
igest that silt eventually led to flooding disasters along the river's lower reaches. Today, every year the river carries 46.4 billion cubic meters of water, merely 8 percent of the 562 billion cubic meters of the Mississippi; at 1,880 cubic meters per second, the Yellow River's discharge rate is only 12 percent of the 15,500 cubic meters per second of the legendarily sluggish Mississippi.21 Given such low water level and low velocity, the river has trouble discharging its heavy silt into the ocean; instead, it deposits silt in the riverbed or spreads it over the land of north China along its course. The flow's inability to transport silt is significantly worsened by the flat, low terrain of the North China Plain. Here, the land stands less than 50 meters above sea level and offers little gradient. Today, nearly 40 percent of the 1.6 billion tons of silt is deposited unevenly over the river's lower reaches, causing the riverbed to rise at a rate of 2–3 centimeters each year. The continuous accumulation of sediment in the past three thousand years has produced a “suspending river” on the North China Plain. This means that a substantial portion of the flow does not stay in the ground but instead stands meters above the surrounding low-lying ground – a phenomenon that historical writings recorded as early as in the second century BCE.