Table 1.

Changes in natural and human factors of the Yellow River over historical times

Period	Major dynasties	Socio-economic changes	Middle river			Lower river
			Population density (persons per km2)	Area south of the northern boundary of FGTZ (percentage)	Grain yield (kg/ha)	Sedimentation rate (mm/a)	Number of avulsions	Number of breaches	Number of river management activities
21st–5th Century bc	Xia, Shang, Western Zhou	Agriculture, state		<38		1–2	1		3
5th Century bc–70 ad	Warring States, Qin, Western Han	Plow, embankment, the Great wall, centralized imperial state, “farming and fight” military policy	<26	38–88	Western Han: 1050	2–4	5	9	7
70 ad–1128 ad	Eastern Han, Tang, Northern Song	Northern Song: steep hillslop cultivation	<36	60–97	Northern Song: 1400–1700	2–20	12	110	144
1128 ad–1855 ad	Ming, Qing	River control paradigm “restrict the current to attack the silt,” river management system	36–80	80–100	450–1000	20–30	40	419	1018
1855 ad–the present	Qing, PRC	Damming, industrialization, agricultural modernization	80–235	100	1000–3000	30–200	1	96	2120

Historical population densities in the middle river are estimated by dividing registered population sizes (Fig. 3c) by the middle basin areas south of the northern boundary of FGTZ in different periods (Fig. 5). Grain yields in the middle river are estimates on the basis of accounts in The Twenty-five Histories (Perkins and Wang 1969; Ning et al. 1999). The sedimentation rates of the lower river channel are after Xu (1998, 2003). The number of avulsions is the total number of historical records of natural and artificial avulsions; the number of breaches is the total number of historical records of natural and artificial breaches. The number of the river management activities is the sum of historical records of “construction” and “regulation”