Study Area

The Heihe River originates from the Qilian Mountains on the northern edge of the Tibetan Plateau, flows through the Zhangye Basin, Jiuquan Basin, and Jinta Basin, and finally injects into the territory of Ejin Banner in the Inner Mongolia Autonomous Region. It is the second largest inland river in China [15]. The Heihe River Basin is the second-largest inland basin in the northwest region of China, geographically located between 96°04′~102°00′E and 37°41′~42°42′N, with a total area of about 14.29×10⁴ km², a total population of 1.425 million, and an irrigated area of 33.5×10⁵ acres. The administrative boundaries include Qilian County in Qinghai Province, Sunan, Shandan, Minle, Zhangye, Linze, Gaotai, Jinta in Gansu Province, and Ejin Banner in Inner Mongolia Autonomous Region, totaling 10 counties (banners) [16]. The basin belongs to the mid-temperate continental arid climate, with a dry climate, scarce precipitation, and concentrated June-September strong solar radiation, and a large temperature difference between day and night. At present, the basin has formed major oasis areas such as Shandan-Minle, Ganzhou-Linze-Gaotai, Jiuquan, Jinta-Dingxin, and Ejin Banner. Among them, Jinta Oasis, Dingxin Oasis, and Ejin Banner Oasis are located in the lower reaches of the basin, while other oases are located in the middle reaches of the basin. The Heihe River has nurtured rich pastures in its upper reaches and nourished fertile farmland in its middle reaches, making Zhangye an important grain-producing area in western China (Figure 1) [17, 18].

Fig. 1.

Geographical map of the Heihe River Basin.

Date Sources and Date Processing

Site Visit Information

In order to verify the accuracy of the location of agricultural facilities in some of the literature and historical drawings, a site examination was conducted in the Heihe River Basin from May 2011 to July 2022. Some historical sites were surveyed on site, and some more objective information on agricultural facilities was obtained, including the location of major water sources, the location and length of old irrigation areas, and the location of some water conservancy facilities. The main routes of the examination are shown in Figure 2.

Fig 2.

Field survey route.

Study Methods

Spatial and Temporal Variation Characteristics of Agricultural Land

The spatial visual representation and mathematical statistical analysis of agricultural land in the Heihe River Basin at different periods since the Han Dynasty were performed using the GIS spatial overlay method (Figure 3). It was found that the agricultural land in the Heihe River Basin changed significantly throughout the study period. Spatially, it was mainly concentrated in the southeastern part of the basin, and its changes showed a trend of decreasing and then increasing, and the overall area showed a trend of increasing. In different historical periods, agricultural land was distributed in the upstream, midstream, and downstream areas from the Han Dynasty to the Yuan Dynasty. While agricultural land was mainly distributed in the upstream areas, beginning with the Ming Dynasty. The Heihe River Basin had a better ecological environment in the early downstream areas that was suitable for agricultural development. However, the ecological environment deteriorated in the modern age, and the downstream areas became unutilized and bare land, unsuitable for agricultural land development and exploitation. In terms of quantitative changes, from the Han Dynasty to the Song Dynasty, the area of agricultural land in the Heihe River Basin decreased continuously from 1702.74 km² to 560.47 km², with an obvious trend of decrease. From the Yuan Dynasty to the People’s Republic of China, the agricultural land in the Heihe River Basin expanded very rapidly and grew faster, with the area increasing from 614.32 km² to 6396.54 km². In the People’s Republic of China period, the change rate of agricultural land area was greater than 2, indicating that the expansion rate of agricultural land in the Heihe River Basin was the fastest. Table 1 provides detailed statistics on the area and changes of agricultural land in different periods.

Spatial overlay analysis of agricultural land in the Heihe River Basin in each adjacent period since the Han Dynasty using the ArcGIS10.4 platform yielded the results shown in Figure 4 and Figure 5. It can be seen that the intensity of agricultural land area change in the Heihe River Basin fluctuated greatly during the study period, but the intensity of agricultural land change varied in different periods. Among them, the dynamic attitude of agricultural land change was negative from the Han Dynasty to the Song Dynasty, indicating that the area of agricultural land in that period was decreasing, and after the Song Dynasty, it showed an obvious increasing trend, especially in two obvious increasing periods from the Ming Dynasty to the Qing Dynasty and from the Republic of China to the People’s Republic of China. Figure 4 shows the change in agricultural land in two adjacent periods. It can be seen that agricultural land has increased and decreased in different historical periods, but its increasing trend is more obvious from the Qing Dynasty, and the increasing location is mainly concentrated in the upstream area of the Heihe River Basin.

Fig. 3.

Spatial distribution of agricultural land in the Heihe River Basin since the Han Dynasty.

To more intuitively represent the changes in agricultural land in the Heihe River Basin during the study period, this paper calculated the geometric centers of agricultural land in the Heihe River Basin in each period using the spatial statistics tool in ArcGIS. Meanwhile, this paper obtained the geographic coordinates and distances of the center points in each period, and the results are shown in Figure 6. It can be found that the location of the center of agricultural land in the Heihe River Basin changed significantly over time, with the center of agricultural land moving westward by 49.54 km from the Han Dynasty to the Jin Dynasty, and moving northward by 28.78 km from the Jin Dynasty to the Tang Dynasty. From the Tang Dynasty to the Song Dynasty, the center of agricultural land moved 158.77 km to the northeast. The center point of agricultural land moved 59.47 km to the west from the Song Dynasty to the Yuan Dynasty. The center point of agricultural land moved the most between the Yuan Dynasty and the Ming Dynasty, 162.57 km to the south. From the Ming Dynasty to the People’s Republic of China periods, the center points were concentrated in the southern part of the basin, with less variation, and the distance between them was within 20 km.

The most important factors affecting agricultural land are temperature and precipitation, which are mainly related to the terrain and climate of the Heihe River Basin. It is characterized by a continental climate surrounded by mountains and far from the sea. The southern part is located in the Qilian Mountains, with more precipitation, a low temperature, and weak evaporation [7, 22]. The downstream area is extremely dry, with less precipitation, more wind, and a large temperature difference between day and night, which can directly affect the growth of vegetation, while precipitation and temperature can affect the temporal and spatial distribution of hydrology and water resources. As shown in Figure 7 and Figure 8, most of the precipitation in the middle reaches of the Heihe River fluctuates around 100mm, making it difficult to supply water to agricultural land. But in the upper reaches of the Heihe River Basin Qilian Mountain area, rain is rich and is the main source of agricultural land water supply. The variation trend of precipitation is basically consistent with that of farmland areas. Higher temperatures will also restrict the growth of vegetation. Under the synergistic effect of temperature and precipitation, the temporal and spatial changes of agricultural land were changed.

Fig. 4.

Dynamic attitude of agricultural land change in the Heihe River Basin.

Fig. 5.

Spatial changes of agricultural land in the Heihe River Basin since the Han Dynasty.

Spatial and Temporal Variation Characteristics of Irrigation Canals

Agricultural development is often inseparable from water resources, and irrigation canals, which convey water resources for agricultural production, are very important agricultural facilities. In this paper, the number of irrigation canals in the Heihe River basin in various periods was statistically analyzed by the nuclear density analysis method, and the results are shown in Figure 9 and Table 2. The study shows that the spatial distribution of irrigation canals in the Heihe River Basin gradually evolved from point-like distribution to surface-like distribution and constantly clustered in the southeastern part of the basin. The number and area of irrigation canals increased significantly during the Yuan Dynasty, and the spatial location was similar to the distribution trend of agricultural land. The number of irrigation canals increased slowly, and the length of irrigation canals increased from 98.96 km in the Han Dynasty to 165.30 km in the Song Dynasty, mainly due to the low level of social and technological development at that time, and the fact that the Heihe River Basin was located at the border with more social unrest, which led to the decrease of population, and thus the demand for agricultural facilities, such as irrigation canals. The demand for agricultural facilities, such as irrigation canals, decreased. From the Song Dynasty to the Yuan Dynasty, the population recovered, but the number of irrigation canals was basically the same as in the Song Dynasty because there were many uprisings and social unrest in the latter part of the period, so there was no major water development. From the Ming Dynasty to the People’s Republic of China period, the length of irrigation canals increased rapidly, from 2051.78km to 3267.69km in the Republic of China period, the total length increased by 19.76 times compared with the Song Dynasty, mainly due to the rapid development of social and economic development in this period. The period of science and technology has been developed and has higher productivity, while social stability and the cultivation of high-yielding food crops drives a rapid increase in population. The number of irrigation canals also increased rapidly due to the expansion of agricultural land and the increasing demand for related agricultural facilities.

Fig. 6.

Changes in the agricultural land centers in the Heihe River Basin since the Han Dynasty.

Fig. 7.

Average annual variation curve of precipitation.

Fig. 8.

Average annual temperature change curve.

Fig. 9.

Irrigation channel changes in the Heihe River Basin in different periods.

To deeply analyze the changes in the number of irrigation canals in the Heihe River basin in each period, statistical analysis of the nuclear density of irrigation canals in different periods was carried out in this paper, and the results are shown in Figure 10. It showed that the density of irrigation canals in the Heihe River basin shows a change characteristic of increasing and then decreasing with the passage of time. From the Han Dynasty to the Qing Dynasty, the density of irrigation canals in the Heihe River Basin increased from 0.082 to 0.520 and then decreased from 0.520 to 0.398 during the Republic of China to New China. In the Ming Dynasty, the density of irrigation canals increased from 0.211 in the Yuan Dynasty to 0.413, which was double the density of irrigation canals in the Yuan Dynasty, and reached its maximum density in the Qing Dynasty. During the period from the Republic of China to the People’s Republic of China, the density of irrigation canals in the basin decreased due to the abandonment of some canals that had no irrigation function, the systematic optimization of the construction of irrigation canals in the basin, and urban expansion.

Changes in water resources can directly determine changes in river tributaries and irrigation channels. The paper statistically analyzed the annual variation characteristics of surface runoff from the Han Dynasty to the People’s Republic of China for more than 2000 years. The results are shown in Figure 11. Most of the annual runoff is concentrated in the 10-20×109m³/a fluctuation. Two troughs occurred in the Jin Dynasty and the Tang Dynasty, indicating that water resources decreased during this period, and the corresponding water sources and irrigation channels also changed significantly. However, in the Ming Dynasty, the Qing Dynasty, and the Republic of China, there was a small peak of runoff, which was consistent with the change of irrigation canals.

Natural disasters have a certain impact on the agricultural facilities in the Heihe River Basin, which can destroy the agricultural land in the region in a short time and even lead to a change of water source. Natural disasters in the Heihe River Basin mainly include earthquakes, sandstorms, hail, etc., which are mainly caused by climate change [4]. According to the statistics on the occurrence times of various disasters (Figure 12), drought and flood disasters occurred 251 times in the Heihe River Basin, of which 71 were waterlogged and 180 were drought [23]. It showed that the drought disaster is the main natural disaster in the basin. Drought and flood disasters in the river basin play an important role in promoting the spatio-temporal change of agricultural facilities and are also one of the main factors causing the change of social life.

Spatial and Temporal Characteristics of Watershed Changes

The kernel density analysis and dynamic calculus methods were used to analyze the characteristics of watershed changes during different periods. The results are shown in Figure 13, which reveal noticeable fluctuations in watersheds within the Heihe River Basin from the Han Dynasty to the establishment of the People’s Republic of China. The main areas of change are concentrated in the upper reaches of the Heihe River Basin. By examining the locations of increased watersheds, it is evident that they were predominantly situated where rivers connect with agricultural land. The primary approach involved establishing connections between different water systems, further facilitating river flow. Additionally, artificial irrigation channels were constructed between rivers to improve waterway clearance. In terms of the study period, the watersheds remained relatively stable from the Han Dynasty to the Yuan Dynasty. However, an evident increase in watersheds occurred from the Ming Dynasty onward, reaching its peak during the era of the People’s Republic of China. The article also presents the total length of watersheds during different periods, as illustrated in Figure 14. The research findings indicate that the length of watersheds fluctuated between 2300 km and 2350 km from the Han Dynasty to the Republic of China period. However, during the era of the People’s Republic of China, there was a significant surge in length, with an increase from 2350 km to 2514 km. This represents a growth of 164 km, reflecting the substantial increase in demand for watersheds in the Heihe River Basin due to rapid agricultural development and population growth during modern times. It also highlights the expansion of agricultural land, which has resulted in a greater number of tributaries in the watershed.

Fig. 10.

Change in irrigation channel density in the Heihe River Basin.

Fig. 11.

Change in average annual runoff in the historical period.

Fig. 12.

The number of disasters and the years between them.

Fig. 13.

Spatial variation characteristics of water source sites.

Spatial and Temporal Characteristics of Water Conservancy Facilities Changes

The geometric center migration method was used to determine the center points of water conservancy facilities during different periods, as depicted in Figure 15 and Figure 16. The research revealed that the water conservancy facilities of the eight dynasties were concentrated in the upper reaches of the Heihe River Basin, displaying a ‘loop-shaped’ variation in their center points. The center points migrated approximately 99.46 km southeast from the Han and Jin Dynasties to the central positions during the Tang, Song, and Yuan Dynasties. Subsequently, they shifted northwest by 44.95 km to the center during the Ming Dynasty, then migrated southwest by 77.55 km to the center during the Qing Dynasty, and finally moved southeast to the center during the Republic of China period. In terms of the number of major water conservancy facilities, the highest number was observed during the Qing Dynasty, with a total of 12 locations, while the lowest number was during the Tang, Song, and Yuan Dynasties, with only three locations. The variation in the quantity of water conservancy facilities differs from the number of agricultural land and irrigation channels during each period. This difference may be attributed to partial data missing, but it also reflects the interplay between agricultural development, socio-economic factors, and social infrastructure during that time.

Fig. 14.

Changes in water source sites by period.

Fig. 15.

The number of water conservancy facilities varies from period to period.

Fig. 16.

Central point migration diagram of water conservancy facilities.

Overall Characteristics of Agricultural Facility Changes in the Heihe River Basin

This paper integrates agricultural land, irrigation channels, watersheds, and water conservancy facilities and produces a spatial distribution map of agricultural facilities in the Heihe River Basin, as shown in Figure 17. It can be observed that agricultural facilities in the Heihe River Basin have been relatively comprehensive since the Han Dynasty, primarily developing and evolving in areas with flat terrain and abundant water resources. The main agricultural facilities form two agglomerated regions within the basin: one in the southern part, characterized by a strip-like distribution, and another in the northern part, exhibiting a point-like distribution. During the Jin Dynasty, the scale of agricultural facilities in the Heihe River Basin decreased, and the spatial distribution characteristics were similar to those of the Han Dynasty. By the Tang Dynasty, the distribution of agricultural facilities in the Heihe River Basin had evolved from strip-like agglomeration during the Han and Jin Dynasties to multiple scattered points of concentration. During the Song and Yuan Dynasties, the distribution of agricultural facilities in the Heihe River Basin resembled that of the Tang Dynasty, with a predominant concentration of point-like clusters. However, starting from the Ming Dynasty until the era of the People’s Republic of China, the distribution of agricultural facilities gradually reverted to a strip-like agglomeration, and the number of various agricultural facilities increased rapidly. Nevertheless, in the northern region of the basin, the main agricultural facilities were abandoned and disappeared.

Throughout the entire study period, agricultural land had the largest scale among agricultural facilities in the Heihe River Basin, followed by irrigation channels, which showed an increasing trend in quantity. On the other hand, there were significant differences in the distribution of watersheds, with the fewest observed during the Ming Dynasty and reaching the highest total length during the era of the People’s Republic of China. The distribution of water conservancy facilities exhibited noticeable fluctuations and a relatively small-scale distribution. The periods with the highest number of water conservancy facilities were the Qing Dynasty and the Ming Dynasty, followed by the Han Dynasty and the Jin Dynasty. The Tang Dynasty, Song Dynasty, and Yuan Dynasty had the fewest number of water conservancy facilities, and there were no significant changes in length during these periods.

The Influence of the Main Social Economic Factors on Agricultural Facilities

Land Taxation Policy

China is a large agricultural country with a farming civilization spanning more than 5,000 years, and the changes in the land system have largely influenced the development and changes of the Chinese economy. The government of each dynasty has formulated corresponding economic systems, including land, taxation, and corvée systems, among which the land and taxation systems directly affect agricultural production and play an important role in the development and evolution of agricultural society [13].

The Han dynasty, while practicing rest and recuperation, followed the name field system of the Qing dynasty, which was based on the military title system and granted fields according to household registration. At the same time, different titles and different amounts of land were assigned according to military merit, and the land granted by the state became private possession, and the state would not take it back. In addition to allowing people to open up land, land could be bought and sold freely, which increased the enthusiasm of farmers in farming [22]. From the Jin dynasty to the Northern and Southern dynasties, the state reduced field rents, abolished harsh taxes, issued equal-field decrees, and implemented the equal-field system, allocating land to peasants according to gender and age. The main part of these lands was only allowed to be used and not to be bought and sold, and the peasants who received the fields had to pay rent and taxes to the state and perform corvée and military service [13].

From the evolutionary development of land policies in various historical periods (Figure 18), the land system in the region has been continuously modified and improved since the Han dynasty, with farmers receiving more land for cultivation and reduced taxes, while farmers’ rights and interests in farming have been systematically guaranteed and their motivation to cultivate has increased, promoting local agricultural development.

Fig. 17.

Spatial distribution of agricultural facilities in the Heihe River Basin.

Military Warfare

During the Han dynasty, the Heihe River Basin was located between the four major regions of Guanzhong; the Western Region, Inner Mongolia, and Huangshui River, with a collection of roads, dangerous terrain, and developed agriculture and animal husbandry. It also had a high strategic location value. There are 23 documented battles related to the area recorded in the literature [10]. Since the Han dynasty, the operation of the Heihe River Basin and the northwestern region by successive central governments was full of military colors, the fundamental purpose of which was to guarantee the security of the frontier through the border defense system, so the agricultural development of the area had special military defense attributes. Figure 19 shows the main military situation in different periods. It can be seen that the stability of the regional situation has the most direct impact on agricultural production. Regional unrest and frequent warfare will directly lead to a sharp decline in population, land abandonment, and agricultural production interruptions. Only regional stability, population concentration, technological development, and agricultural development will be faster.

Fig. 18.

Evolution of the land/tax system in major dynasties.

Fig. 19.

War and agricultural development in the Heihe River Basin in the historical period.

Population

Population is the main body of social production and life. In a social economic system dominated by agriculture, population fluctuations will have a huge impact on agricultural production and agricultural facilities. During the Han Dynasty, the Central Plains regime had a strong control over the frontier, social stability attracted a large number of foreigners and there was a steady growth in population. During the Jin Dynasty, due to frequent wars, social unrest, and uncertain population migration, the total population decreased significantly. Combined with the literature records [16, 23], according to the above-mentioned estimation results for each period, the population of the Heihe River Basin in the Tang and Yuan dynasties was also small. The population data of Heihe in the Ming Dynasty can be found in many local records, among which “Re-repairing the New Records of Suzhou·Hukou” and “Re-publishing the records of Gan Zhen·Sui Ji” are more systematic, “Ganzhou Fu Records”, “Five Liang Kao Zhi and six De Records” have scattered records. At the end of the Ming Dynasty and the beginning of the Qing Dynasty, after years of war and natural disasters, the whole of Hexi was barren and sparsely populated. After the late Kangxi period, the social order was relatively stable. In the fifty-first year of Kangxi, the edict of “breeding people and never adding Fu” was issued, and the system of “sharing Ding into mu” implemented in the Yongzheng period also promoted population growth in the valley [24]. During the Qianlong period of the Qing Dynasty, the population of Hexi once again flourished. After the “Kangqian” Prosperous Age, the population of the basin increased by leaps and bounds, reaching the highest population in feudal society. During the period of the Republic of China, due to the special geographical environment and good foundation of agriculture and animal husbandry, the Heihe River Basin was a relatively “solitary” place, which attracted a large number of foreigners and made the population grow rapidly [25].

Fig. 20.

Population scale of the Heihe River Basin in the historical period.

According to the relevant literature, this study estimated the population of the river basin in each period and found that the population change from the Han Dynasty to the Republic of China showed a trend of decreasing first and then increasing (Figure 20). The large increase in population makes the need for agricultural land increase, so the best reclamation, the expansion of arable land to the mountain area, is also a kind of promotion of agricultural development. Therefore, the change in population is basically consistent with the development and change trend of agricultural facilities.