*2.1. Cities of the Lower Yellow River Floodplain*

The Yellow River, known as "China's sorrow" because of the misery caused by its periodic flooding, traverses the lower Yellow River floodplain. During the Holocene, in the lower reaches of the Yellow River, the course of its flow fluctuated frequently over the North China Plain, with flows into the Bohai Sea in the Northeast, or into the Yellow Sea in the Southeast. The area covered by the river basin, which is bounded by Tianjin to the north and Jianghuai to the south, comprises some 250,000 km<sup>2</sup> and had a very important impact on the social and economic development of the region [12,13]. The lower Yellow River in history has been characterized as frequently shifting course with overflows leading to floods. According to records in historical documents, catastrophic levee failure occurred 1593 times and major shifts of the channel occurred 26 times during the past 3000 years [14–18] (Figure 1). These changes brought unimaginable catastrophes to villages, cities, and their peoples, the survival circumstances of which, thus, merits detailed study for future benefit.

**Figure 1.** Locations and frequencies of flood events in the lower Yellow River. The base map is from the Harvard database https://doi.org/10.7910/DVN/Q9VOF5. The data in the figure is from References [14,16].

Furthermore, the current status of the ancient cities in the Yellow River floodplain were divided into three categories, as shown in Table 1, depending on the location of water: 1) lakes/ponds within the city wall, 2) lakes/ponds encircling the city wall, and, 3) the old city turned into lakes (Table 1).


**Table 1.** Remaining form of City in the Yellow River floodplain [19–22].

### *2.2. Kaifeng City*

Kaifeng city, extending from 34◦11 N to 35◦01 N and 113◦52 E to 115◦15 E in Henan province, is situated on the southern bank of the Yellow River, about 70 km east of the provincial capital, Zhengzhou, and nearly 650 km southwest of Beijing. (What is now Kaifeng has had a number of different names. For example, it was Yiyi in the Spring and Autumn Period, Daliang in the Warring and States Period, Bianzhou in the Sui and Tang dynasties, Dongjing in the North Song dynasty, Bianjing in the Jin dynasty, Bianliang in the Yuan dynasty, and Kaifeng in the Ming and Qing dynasties.) As an

ancient capital and one of the most important cities in ancient China, Kaifeng city is often referred to as "the Capital of the Eight Dynasties". Especially in the Northern Song dynasty Kaifeng was arguably one of the most important places in the world. (The Chronology of Chinese Dynasties—the Western Zhou Dynasty (1046 BC–771 BC); the Spring and Autumn Period (770 BC–476 BC); the Warring States Period (475 BC–221 BC); the Qin dynasty (221 BC–207 BC); the Western Han dynasty (206 BC–24 AD); Sui and Tang dynasties (581 AD–907 AD); the Northern Song dynasty (960 AD–1127 AD); the Jin and Yuan dynasties (1115 AD–1368 AD); the Ming dynasty (1368 AD–1644 AD); and the Qing dynasty (1636 AD–1912 AD).), From the Yuan, Ming and Qing Dynasties to 1954 AD, Kaifeng was the provincial capital of Henan province, but this changed in 1954 AD, when the provincial capital moved westward to Zhengzhou and Kaifeng became a regional level city.

Since the third century BC at least seven floods have devastated Kaifeng city (Table 2). From the Southern Song Dynasty to the late Qing dynasty, Yellow River flooding has occurred more than 300 times near Kaifeng city, more than 10 of which besieged the city whilst six actually entered the city [23–25]. In addition, more than 10 of these floods entered the protection earth ramparts and besieged Kaifeng city. During 1448–1492 AD, the Yellow River traversed around Kaifeng city and separated Kaifeng from the north bank of the Yellow River. Kaifeng was subjected to frequent flooding by the Yellow River after the Jin and Yuan dynasties, and this gave rise to complex changes to its urban forms. There were seven major flood disasters, two of which, in 225 BC and 1642 AD, destroyed the whole city. In 1841, the city was inundated for about 8 months, but it was not until 1843 that the walls were reconstructed, and by this time, the urban form of Kaifeng, including the earth rampart, brick city wall and lake, became the critically important flood-adaptability landscape. More significantly, survivors rebuilt a new city on the same site after each flood, resulting in the old city buried in the cultural layers of different periods (i.e., the seven major floods), forming what has become known as the "city overlap city" landscape. Six Kaifeng cities now lie buried under silt with the oldest "fossil" city buried 10 m underground [26]. Nowadays, the flood disasters of the past are almost totally forgotten, but the suspended river landscape, low city wall, the huge lake in the city together with the "city overlap city" landscape significantly contribute to the Yellow River's natural heritage as well as to the cultural heritage of Kaifeng city.

