Changing mechanisms of agricultural water use in the urbanization and industrialization of China

In China, irrigation has always been a dominant factor in guaranteeing agricultural production and promoting the country's economic and social development. Irrigated land accounts for approximately 45% of China's total agricultural acreage. The annual grain output occupies 75% of the country's total grain output, and the annual output of commercial crops occupies more than 90% of total agricultural output (Liu et al., 2006; Wang, 2009). Although the economic benefits gained from agricultural water are not especially high, guaranteeing agricultural water resources is a vital task for guaranteeing grain safety in China (Jiang et al., 2012). Ensuring agricultural water is necessary to achieve the stabilization of grain production, and is an objective requirement of the growing demand for grain. The farmland water resource per unit area in China is about 67% of the world average, while the water resource per unit of irrigated area is lower, only 19% of the world average. China's irrigated farmland covers 5.467*10⁵ km². In a normal year, the agricultural water deficit is more than 300*10⁸ m³, and about 6.67*10⁴ km² of irrigated farmland is in severe water shortage. From 2002 to 2012, the average annual agricultural drought area was approximately 2.467*10⁵ km², leading to a grain-output loss of approximately 3 × 10¹⁰ kg (Hu et al., 2013). Urbanization and industrialization in China have increased in recent years. Over the last 20 years, these processes have significantly changed the land use and land cover patterns in rural areas, particularly in the areas surrounding large cities in Eastern China. This is largely due to the continually shifting government policies and farmers' changing economic interests (Lu et al., 2011). In some of these areas, there are serious discrepancies between water supply and water demand, and this issue exacerbates the constraints of agricultural water supplies (Saysel et al., 2002; Chadwick et al., 2006; Jia & Huang, 2011; Su et al., 2011; Wang et al., 2015). The transformation towards further urbanization and industrialization represents a critical juncture for agricultural modernization and development in China (Tian & Wu, 2015; Yan et al., 2015). De Souza (2015) studied evidence of complementary growth between agriculture and industry in developing countries, and concluded that growth in agriculture benefits the manufacturing sector by improving domestic terms of trade, increasing the shares of investment and savings in gross domestic product (GDP), and through bolstering the capacity of individual countries to import industrial inputs. As processes of industrialization, urbanization, and agricultural modernization continue to develop, ensuring agricultural water use security and national food supply security has become an even more vital mission for China, today and looking to the future. Chinese modernization mandates a synergistic development of industrialization, urbanization, and agricultural modernization. Urbanization is a long-term historical process as well as a complex engineering system – it is simultaneously driven by industrialization and supports industrialization in return. Food security is also a key issue in urban development. Without agricultural stability, there can be no development or prosperity, rendering industrialization and urbanization initiatives useless. By providing an in-depth mechanism analysis on the impact of urbanization and industrialization in China, specifically on how these factors apply to agricultural water use, this paper aims to contribute fungible strategies that China can pursue to ensure security for agricultural water use and grain production in this age of development.

China's natural terrain and water/soil resources are unevenly distributed, which leads to massive differences in the capacities of various regions to achieve socio-economic development. This means that the comprehensive development and utilization of local land and water resources manifest in diverse ways across regions. China has 13 major grain producing areas (or provinces), which are Liaoning Province, Hebei Province, Shandong Province, Jilin Province, Inner Mongolia Autonomous Region, Jiangxi Province, Hunan Province, Sichuan Province, Henan Province, Hubei Province, Jiangsu Province, Anhui Province, and Heilongjiang Province. Grain production in these 13 provinces (also referred to as autonomous regions) constitutes approximately 75% of China's total grain production.

This paper selects and analyzes cases from the main grain production areas first by providing a summary of the relevant national-level factors. By taking into consideration the distribution of climate conditions, major grain producing areas, water resource conditions, water and soil resource balances, and the degrees of economic and social development, as well as other factors (Mizyed, 2009; Tian, 2015), China can be functionally divided into four key regions. These are the Huang-Huai-Hai region, the northwest region, the northeast region, and the southern region. In the Huang-Huai-Hai region (the Yellow River-Huaihe River-Haihe River basin), water resources are deficient in general, while cultivated land resources are abundant; this region is the primary area for wheat, corn, and rice production in China, with a relatively high level of eco-social mobility, and is one of the most important regions for economic development in the country. In the northwest region, water resources are extremely poor and the ecological environment is particularly fragile. Agriculture there depends almost entirely on irrigation, and the regional economy comparatively lags behind. The northeast region has comparatively rich water and land resources, and is the largest corn, high-quality rice, and soybean-producing area in China; it is also an old heavy-industry base, where urbanization and industrialization are relatively advanced. In the southern region, precipitation is comparatively abundant, although the distribution of annual precipitation is uneven. Agriculture there is already highly developed, and the level of urbanization and industrialization is relatively high, though regional development is uneven.

This paper uses statistical data from the ‘China Statistical Yearbook’, ‘China Water Resources Bulletin’, ‘Yellow River Basin Water Resources Bulletin’, ‘Yangtze River Basin Water Resources Bulletin’, ‘Haihe River Basin Water Resources Bulletin’, and ‘Songhuajiang and Liaohe River Basin Water Resources Bulletin’. The data regarding water resources, agriculture, industry, domestic and total water use analyzed in this study were gathered from Chinese water resources bulletins between the years 1997 (when publication of the bulletins began) and 2012. The economic and social data from the selected provinces for the timeframe of 1997 to 2014 were collected from the China Statistical Yearbook and the Statistics Bureau's website.

In this article, the agricultural water use comprises farmland irrigation water, woodland and grassland irrigation water, fishery water, and livestock water. During the study period, the proportion of farmland irrigation to total agricultural water use was around 90% (no less than 87%); hence, the change in farmland was considered as the dominant factor in determining agricultural water use.

Statistical analysis is the primary research method used in this study, and includes indicator selection, regression analysis, and trend analysis. This method was chosen for its simplicity and effectiveness, features that enable an assessment of the impact of urbanization and industrialization processes on agricultural water resources in China. In this paper, two typical indicators are employed: urbanization rate and proportion of the added value from secondary and tertiary industries to China's GDP. Urbanization rate mainly indicates changes in regional population structures, while proportion of added value typically reflects the changes in regional industrial structures. These indicators were chosen because industrial development in the economically developed areas of China is gradually entering a post-industrial phase, where the rate of industrialization may slow as their social economies develop further. Using only the rate of industrialization does not allow for a comprehensive understanding of China's regional economic development status. Studying it in conjunction with the added value of the secondary and tertiary industries in the GDP enables a more comprehensive analysis of the degree of regional economic development, as is directly linked with water use rates for cities and industries (Srinivasan et al., 2013).

This paper excluded climate as a factor except in cases of individual extreme weather events. We took this approach because, since 1990, with technological advances, artificial factors have replaced natural climate factors to become the dominant force impacting agricultural water use and crop production (Wu & Zhao, 2010). In addition, the climate has complicated impacts on agricultural water use, involving not only multifaceted aspects on particular areas, but also different, sometimes contrasting, effects on different regions (Bär et al., 2015). The role of the climate cannot be determined without a thorough investigation, however, this paper tries to focus on the impacts of human activities based on the understanding that although neglecting the role of the climate may produce some inadequacies in prediction, it should not affect the overall conclusion of our work.

This study attempts to illustrate the impact of urbanization and industrialization processes on agricultural water use and total water use patterns, by analyzing the relationship between agricultural water use and the aforementioned two indicators, particularly how those indicators relate to total water use. Correlations were found at both national and regional levels.

Two distinct periods of agricultural water use in China can be discerned. Up until the 1990s, agricultural water took up a major proportion of the country's total water use. In addition to the fact that there was relatively low competition for water resources due to underdevelopment of industry and urban construction, the issue of water scarcity was generally unknown and unexamined. As a result, agricultural water was chronically under-charged (Jia et al., 2006; Jiang & Liu, 2015) and over-consumed. Since the beginning of the 1990s, however, the rapid development of industry and urbanization highlighted the scarcity of water resources. Due to the comparatively lower benefits of use, the share of total water use once contributed by agricultural water has gradually been overtaken by industrial and domestic use.

The proportion of the added value from the secondary and tertiary industry in China's GDP is comparatively high for Beijing City, and reached 99.2% in 2012. The economy of Jiangsu Province was developed rapidly, and ranked second after Beijing City, at 93.7%. The economy of the Hebei, Ningxia, and Jiangxi Provinces also developed rapidly, at a proportion of 90%. The proportion was relatively lower in Sichuan Province, where it increased at a fluctuating rate that reached 86.2% in 2012.

It can be seen that the correlation between agricultural water use and urbanization progress is clearly impacted by regional water resource conditions. In Beijing City, Hebei Province, and Ningxia Province (a city and autonomous regions), water resources are relatively deficient, and development increases demands for water for industrial, domestic and ecological use, which in turn exacerbate the imbalance between supply and demand. Water resources traditionally allocated for agricultural use are increasingly used for non-agricultural activities and industries. A strong correlation was found between agricultural water provision and the rate of urbanization. In Jilin, Jiangsu, Jiangxi, and Sichuan Provinces, water resources are relatively abundant and can generally meet the demands from industrial, domestic, and ecological use, as well as those from agricultural use.

Since economic reforms have come into effect in China, urbanization has caused a rapid movement of the population from rural areas to urban settings (Brückner, 2012; Chen et al., 2015). In 1997, the urban population of China was 369.89 million, while the rural population was 866.37 million. The proportion of the urban population within the total population was 29.9%. By 2012, the proportion of the urban population had increased to 52.6% of the total population. Compared with the figures from 1997, the proportion of the urban population within the total population increased by 22.7%, at an average increase rate of 1.4% per year.

The amount of domestic water use for urban residents is considerably higher than that of rural residents. According to the China Water Resources Bulletin, in 2012, the average urban domestic water use per capita was 216 L/d, while the rural domestic water use per capita was 79 L/d, given the weighted distribution of the population residing in urban areas. The expansion of the urban population precipitated a significant increase in urban domestic water use. Water demands in the urban ecological environment also increased significantly, as living standards improved (Braud et al., 2013). In regions that experience water shortages, resources originally allocated for agricultural use begin to be used for non-agricultural purposes, such as supplementary urban water requirements. This is the key reason for the proportional decrease in agricultural water use since the advent of urbanization and industrialization in China.

Industrialization has precipitated a continuous decrease in the proportion of water resources that are used for agricultural activities. Changes to the structure of the industry directly affect agricultural water use. Since the 1990s, the emphasis of Chinese industrial structures has shifted towards expansion, with more investment in basic industry and infrastructure, for the purpose of accelerating the developmental steps of tertiary industries and improving industrial structures (Zhao et al., 2014). Under the National Industrial Structure Adjustment Policy, the proportion of primary industry was shown to continuously decrease from 18.3% in 1997 to 10.1% in 2012, with an annual average decrease of 0.54%. Industry grew continuously during this time, as did the service industry's position within the national economy. Under the direct intervention and indirect influence of industrial policy, components of the rural labor force, land resources and water resources were continuously diverted for the sake of developing secondary and tertiary industries (Lu et al., 2011; Su et al., 2011, 2014; Pandey & Seto, 2015). For instance, cultivated land was gradually encroached upon by factories and residential buildings. Incomplete statistics showed that China's cultivated land has been slightly decreasing since 1996. As resources (including farmland irrigational water) and agricultural labor force diminished, so too did agricultural production and demands for farming irrigation, which led in turn to further decreases in agricultural water use.

As urbanization and industrialization have advanced in China, the comparative benefit of agriculture in different sectors of the national economy has depreciated. This shift has influenced stakeholders' enthusiasm for and investment in agricultural water resources (Esmaeili & Vazirzadeh, 2009; Aidam, 2015). In 2012, the industrial benefit and agricultural benefit per cubic metre of water in China was 144.93 RMB and 13.50 RMB, respectively. These figures represent increases of 47.84 RMB for industry and 9.81 RMB for agriculture between 1997 and 2012. From the perspective of regional economic development, local government is now more willing to use limited water resources to support industrial expansion. Water prices also encourage the country's environmental management department to give preferential consideration towards resources involved in urbanization and industrialization efforts. For example, in Shijiazhuang City, Hebei Province, the water price for industrial enterprises in 2012 was 5.33 RMB, and the water price for residents' domestic use was 3.63 RMB. In comparison, the water price for agricultural irrigation ranges from 0.163 to 0.249 RMB (Zhou et al., 2015). This shows that there is more to be gained financially by providing water to urban and industrialized areas than agricultural areas, thus creating an impetus for resources to be directed away from agricultural production and towards industry. Furthermore, in terms of the farmers' own interests, it can be observed that the income that migrant workers earn is considerably higher than the income that can be gained through grain production. This disparity in income rates encourages more farmers to abandon agricultural production in favor of working in cities, thereby further reducing demand for agricultural water resources. Farmers who remain in the agricultural sector are more inclined to replace high water-consuming crops with drought-resistant, water-saving, or economically effective plants, in order to reduce labor and water costs, which result in changes in planting structure and further decrease in agricultural water demand and use.

Urbanization and industrialization present many challenges for agricultural water use. However, these processes also provide the financial, scientific, and technological support that is required to modernize agriculture, and in doing so, arguably facilitate the realization of a more sustainable future for agricultural water usage. Modernization leads to greater agricultural water savings and encourages more efficient water use (Dai et al., 2015; De Souza, 2015). Scientific and technological innovations can affect water conservation greatly; for example, according to the China Water Resources Bulletin and related research (Peng & Gao, 2012), the national average effective utilization coefficient of irrigation water for 2012 was approximately 0.516. This value shows continuous improvement, from 0.463 in 2006, to 0.475 in 2007, to 0.483 in 2008, to 0.493 in 2009, to 0.50 in 2010, to 0.51 in 2011. The role of science and technology in improving water conservation is most prominent in the development of irrigation systems and the water conservation industry.

In light of the analysis detailed above, it is clear that agricultural water use decreases as industrialization and urbanization advance, and so does the proportion of agricultural water use to total water use. However, given that the distribution of water resources and levels of socio-economic development differ between regions, there are differences in the specific changes observed in each region. The total water resources in the Huang-Huai-Hai region are insufficient for the demands of consumption there, particularly because socio-economic development has advanced more rapidly in this area. Consequently, agricultural water use and the proportion of agricultural water that is available exhibit a clear downward trend.

However, the proportion of agricultural water to total water use remains sizable, as agriculture continues to be an integral part of China's society and economy – this proportion is less susceptible to the influence of urbanization and industrialization. Water resources in the northeast region, for example, are relatively abundant and can generally meet the various demands for water, and development has had a minimal impact in this context. There are also abundant resources in South China, and agricultural water use is not as heavily affected by urbanization and industrialized development there either.

Several vectors of activism are required to guarantee the preservation of agricultural water supplies in the face of advancing urbanization and industrialization. These are: establishing and improving the agricultural water resources property rights system and use-control system, recognizing the balance of supply-and-demand for agricultural water, and further improving the efficiency of agricultural water through technological developments and improved project management. These initiatives need to be carried out at both national and local levels.

If the security of water resources is compromised and access to sufficient water supplies is not managed effectively, China's food security is at risk. The Chinese Government has put forward policies designed to strengthen natural ecological spaces (including water, forests, mountains, and grasslands). These are protected and maintained in a unified manner, and the government has formed a property rights system for these natural resources with clearly established ownership rules, well-defined powers and responsibilities, and effective supervision. China has implemented a very strict water resources management system, with targets set for conservation and control of water resource development and utilization to be put into effect between 2020 and 2030. The next steps will require further clarification of water rights, including determining outlines for ownership of agricultural water. This means that the development and utilization of water resources will need to be managed in line with agricultural, industrial, and domestic water use.

Agricultural water use controls should be implemented in order to curb excessive water withdrawal that is linked to urban areas. These measures should strengthen the controls on how agricultural water resources are utilized, and incorporate the extent of use as well as use conversion. For example, controls on agricultural water supplies need to be strengthened according to agricultural water availability and with respect to zoning divisions. However, agricultural water licensing also needs to be improved, and strict management of water use should be implemented. This should be done in order to prevent agricultural water resources being appropriated and consumed for the purposes of urbanization and industrialization. For major grain-producing areas, basic agricultural water supplies should be strictly monitored to ensure that production can continue as expected, particularly that sufficient irrigation water can be provided during the critical period of crop growth.

In order to secure agricultural water use, a strict examination and approval system should be established to discourage citizens and industries from consuming agricultural water without compensation, and guide a more equitable system for this exchange. One major goal of developing policies on agricultural water rights transfer is conservation of irrigation water. Water saved through improving water utilization efficiency can be traded. Under a proper policy, agricultural water saving would be stimulated, and the subsequently expanded efficiency of water use would reduce the impact of irrigation water loss on agricultural production.

Agricultural water rights transfer would likely result in lower agricultural production, and those regions and industries that benefit from rights transfer should be responsible for compensating agricultural producers for their losses. This compensation should follow the principle of ‘beneficiary payment’, namely that compensation comes from water users. The compensation should cover the cost of adopting irrigational water saving measures and equipment renovation, which is the financial fallout from diminished water access, and environmental damage. One example of a venue for this sort of regulation is the recently opened National Water Right Trade Platform, which announces information about the selling and purchasing of water rights, including irrigational water right transfer. An earlier regulating organization is the Water Right Trade Center of Shiyang River Basin, which was established in 2013 and provides information about water right ownership, transfer quantity, price, transaction status, and other related data. The center has greatly benefited the Shiyang River Basin, which suffers from issues with water deficiency, to improve irrigation water saving and compensation for agricultural water loss.

In agricultural water-saving engineering facilities, the channels of anti-seepage treatment should be strengthened, water-saving irrigation technology should be promoted, and field irrigation water utilization should be improved. In the well irrigation area and the conditional canal irrigation district, pipeline irrigation should be vigorously promoted. In the regions with water resource shortages, economic crops, agricultural scale management, sprinkler irrigation, micro-spray irrigation, mulched drip irrigation, and other highly efficient water-saving irrigation techniques and integration techniques should be encouraged. The government also needs to determine a reasonable quota for water irrigation, while improving agricultural water metering facilities and strengthening the management of agricultural water saving efforts.

The construction of irrigation systems and water conservancy projects needs to be carried out in mind of the need to reduce water shortages for engineering uses. There are still instances where water shortages interrupt engineering efforts; the government should invest in the construction of key storage and distribution projects in order to guarantee consistent and sustainable supplies of agricultural water. While engineering is underway, companies should strengthen the operation and management of their projects, highlight standardized management, and improve the functional mechanisms of irrigation systems and water conservation efforts. Modern telemetry and remote sensing, modern communication, and ICT for irrigation systems should be actively promoted in the operation and management of water conservation projects.

Since allocation of soil and water resources differs between regions, the extent of the impact of urbanization and industrialization differs as well (Shao et al., 2015, 2016). The focus of those organizations responsible for overseeing agricultural water security at the regional level should be determined according to regional characteristics, such as natural resources, consumption patterns, and the various progressions of urbanization and industrialization.

There are shortages of water resources in Huang-Huai-Hai region, and agricultural water is mainly groundwater. Increasing domestic and industrial water use has diverted agricultural water, and water industries have become more competitive as resources are scarce in this region. In this setting, the key task of agricultural water management is to determine who has claims on agriculture water resources, and how to guarantee sufficient water supplies for all stakeholders. It should also actively work to locate other water sources and strengthen the safe utilization of unconventional water resources, specifically rain, flood water, reclaimed water, and brackish water.

The South-North Water Transfer Project is a strategic initiative that aims to alleviate water shortages in northern China, particularly in the Huang-Huai-Hai River basin. The South-North Water Transfer Project consists of three subprojects: west line, east line and middle line. The east line project transports water for domestic and industrial use from Yangzhou, Jiangsu Province, to North China, via Anhui Province, Shandong Province, Hebei Province, and Tianjing. By 2050, the east line project is projected to deliver 1.48 × 10¹⁰ tons annually, to compensate for the major water shortage in the eastern part of the Yellow River-Huaihe River Plain. The middle line project transports water from Danjiangkou Reservoir, a reservoir located in the largest branch of Yangtze River, Han River, to Tangbai River Plain and the midwest area of Yellow River-Huaihe River-Haihe River Plain, via Henan Province, Hebei Province, Tianjing, and Beijing. By 2050, the middle line project is projected to deliver 1.3 × 10¹⁰ tons annually, to address the water shortage in the midwest area of the North China Plain. Once water delivery begins, water diverted from agricultural and ecological use would gradually be returned without a resulting undersupply for urban areas. Delivery could be augmented by taking advantage of years with high water flow.

While projects like the South-North Water Transfer Project are able to replenish agricultural and ecological water, certain compulsory policies are also required to catalyze necessary change. For example, some regions proposed larger governmental budgets or an increased water resource fee levied to garner funds for constructing or renovating the matched water conveyance and irrigation engineering in local reperfusion districts. Meanwhile, incentive policies that correct consumers' attitudes would also simulate voluntary return of irrigation and ecological water. For instance, governments of water-receiving areas could provide special subsidies to local water supply construction management institutions that make efforts to improve return rates. In regions that rely heavily on groundwater overdraft, agricultural irrigation water should be gradually implemented as an alternative to groundwater and other water resources.

Urbanization and industrialization have had less of an impact in the northwest region of China, where traditional agricultural production continues to be robust. With the progress in urbanization and industrialization, there has been higher demand for non-agricultural water, which consequently leads to some transfers of agricultural water to urban and industrial use. Agricultural water rights conversion needs to be regulated in the face of these demands. One important step is establishing a compensation system that protects the rights and interests of the agricultural sector. For the northwest region, the key tasks for agricultural water use include the following steps. (1) Regulating water rights conversion: Currently, agricultural water use accounts for a higher proportion of total water use than the sum proportion of urban and industrial water use combined. As industrialization and urbanization extend in this region, agricultural water use will change, and therefore managing this process is vitally necessary. In the water-right conversion processes, a standard procedure for improving the compensation mechanisms of agricultural water right transfer needs to be established. These standards need to be codified in legal rights in order to guarantee sustainable water conservation and investment in irrigation systems. (2) The vigorous promotion of water-saving irrigation engineering and technology: Priority should be given to districts employing gravity irrigation systems such as canal seepage control and water pumping districts attempting to develop pipeline water delivery systems. Areas employing well irrigation should regulate their groundwater yield and develop low-pressure pipe irrigation. Hilly areas are advised to develop rainwater collection and utilization for farmland and supplementary orchard irrigation. Areas with economic crops should develop drip irrigation; piedmonts require the development of self-pressure sprinkler irrigation systems as a matter of priority.

The northeast region has relatively abundant water resources, and water and soil resources are more balanced in terms of supply and demand. However, the exploitation and utilization ratios of water and land resources remain relatively low, and the quantity of effective irrigation areas of farmlands is below China's national average. The northeast region houses China's important and major grain-producing areas – the area undertakes 30% of the new grain production capacity for the nation, and therefore there is more urgency to ensure agricultural water security in this region than in the rest of the country.

The key tasks for this region include the following. (1) Strengthening the construction of irrigation infrastructure engineering projects and expanding irrigated areas. Large and medium-sized irrigation areas and supporting projects need to be strengthened, and surface water irrigation areas should be expanded. Second, there should be moderate construction of new water-source engineering projects and standard farmlands. (2) Adapting to land-scale management, and developing water-saving irrigation systems need to remain priorities. In the northeast, the per-capita area of cultivated land is higher than in other parts of the country, and there are lower rates of effective irrigation areas. The region can moderate the scale of development in this area and undertake intensive land management by establishing a high standard for water-saving irrigation engineering and construction, in order to form concentrated and efficient water-saving irrigation systems.

Water resources in the southern region are relatively abundant, and account for 80% of the country's total water resources; however, agricultural water use efficiency is not high. Some parts of the region, like the southwest, have poor terrain conditions and lack effective water allocation projects, and water diversion is therefore difficult in such conditions. There is still a form of engineering water shortage, which has resulted in increased costs for agricultural irrigation.

In the southern region, key tasks for agricultural water management include the following. (1) Strengthening engineering construction, improving the agricultural water supply through water source engineering, and water system connectivity. (2) Strengthening the construction and management of auxiliary irrigation projects and improving the efficiency of water use. The southern region's water use efficiency is significantly lower than the national average, so the region should actively promote auxiliary irrigation projects that improve the construction and maintenance of irrigation systems. By strengthening the management of irrigation systems, the utilization efficiency of irrigation facilities can be improved, thereby making these systems more beneficial.

Agricultural water resources face unprecedented challenges during the advancement of urbanization and industrialization in China. Urbanization and industrialization impacts agricultural water use by altering where people live, and changing the types of industry that are supported and promoted in the economy, and the comparative benefit of maintaining agricultural production. Analysis of water use on both a national and local level found that, as urbanization and industrialization advance, agricultural water use decreases. This trend is most clear in the Huang-Huai-Hai and the northwest regions, which experience relative shortages in water resources. In the northeast and southern regions, where water resources are relatively abundant, agricultural water use has not been substantially affected by urbanization and industrialization processes, though the proportion of agricultural water to total water use structure has decreased. Agricultural water should be protected, because it risks being overtaken by demands for domestic urban use and industry. Agricultural water use efficiency can be increased by taking advantage of the favorable conditions inherent in urbanization and industrialization processes, such as technological advancements and improved farming and irrigation management techniques. As agricultural water plays an important role in guaranteeing Chinese grain security, it is urgent and necessary to strengthen and secure agricultural water resources.

The researchers would like to extend their thanks to National Science and Technology Major Project of Water Pollution Control and Prevention (2008ZX07207-006, 2012ZX07201-006) and the National ‘973’ project (2015CB452701). The study was also supported by the Chinese National Natural Science Foundation (No. 51522907, 51279208, 51109222), the Research Fund of IWHR (No. 2016ZY02, No. WR0145B502016), and the research project of the Ministry of water resources in China (No. 2013-2).