Spatial-temporal assessment of water footprint, water scarcity and crop water productivity in a major crop production region

Highlights

• Annual water footprint from irrigated agriculture in the whole North China Plain (207 counties) increased over time.

• All counties in the North China Plain faced severe water scarcity.

• Spatial-temporal dynamic of crop water productivity in 207 counties was calculated.

• We developed water consumption method for calculating water footprint.

Abstract

Irrigated agriculture has had an enormous influence on food security, water security and human well-being. Water footprint (how much water is used), water scarcity (how scarce water is), and crop water productivity (how much productivity irrigation adds) are important indicators for evaluating sustainability in irrigated agriculture. Yet these interrelated indicators have not been studied simultaneously at the county level – the basic administrative unit of agricultural planning and water management in countries such as China, India and Japan. To fill this knowledge gap, we performed a demonstration in China's major crop production region, the North China Plain (NCP)'s 207 counties from 1986 to 2010. The results show that the irrigated agriculture's annual water footprint in the North China Plain increased from 53 billion m³ in 1986 to 78 billion m³ in 2010. All counties faced water scarcity during 1986-2010 even as the average crop water productivity increased from 0.90 kg m⁻³ to 1.94 kg m⁻³. There are 173 NCP counties suffering severe water scarcity but still producing significant crop yield with a high water footprint, a red flag of unsustainable irrigated agriculture. This study has implications for revealing potential unsustainable conditions in irrigated agriculture worldwide.

Introduction

Global challenges involving food and water play significant roles in sustainability and human well-being worldwide. The Earth's freshwater resources have been facing tremendous pressure due to increasing consumptive use and water pollution (Steffen et al., 2015; Mekonnen and Hoekstra, 2016). For example, global water withdrawal increased 630 percent during 1900–2010 (Food and Agriculture Organization of the United Nations, 2018). Global food production also faces great challenges since by 2050, 9 billion people would need to be fed (Godfray et al., 2010).

Irrigated agriculture has important implications for both water security and food security. It accounts for more than 70% of the total water use, and more than 90% of total consumptive water use worldwide (consumptive water use is water removed from available supplies without return to a water resource system) (Döll, 2009; Food and Agriculture Organization of the United Nations, 2018). Forty percent of global agricultural production requires irrigation (Viala, 2008).

Much effort has been made to improve irrigated agriculture's performance on water consumption and crop yields for more sustainable development. Many public policies have been applied and billions of dollars spent to save water in irrigated agriculture (Ward and Pulido-Velazquez, 2008). The water footprint, water scarcity, and crop water productivity are used as indicators to assess water and food sustainability. A product's water footprint (WF) is the total volume of freshwater consumed to produce the product (Liu et al., 2009; Mekonnen and Hoekstra, 2011). WF includes not only direct water consumption of products, but also indirect water consumption – water indirectly consumed and water polluted throughout the production chain. Water scarcity shows a shortage of renewable fresh water compared to water demand (Raskin et al., 1996; Damkjaer and Taylor, 2017). We measure agricultural water use against renewable agricultural water resources to represent the extent of water scarcity in agriculture (Raskin et al., 1996; Damkjaer and Taylor, 2017). Crop water productivity refers to the amount of crop produced per unit of water used. China is challenged to increase crop water productivity to relieve pressures that agriculture puts on water resources while increasing crop production (Wang et al., 2014). Evaluating water footprints presents a comprehensive picture of the relationship between water consumption and human appropriation, because a water footprint includes both direct water consumption of products and water indirectly consumed and polluted during production. Assessing the impacts of water scarcity helps pinpoint vulnerable hotspots for solving the problem. Exploring crop water productivity can facilitate understanding the trade-offs between food production and water consumption. Holistically, understanding all three variables can illuminate pathways to alleviate conflicts between water security and food security.

Many studies have focused on water footprint, water scarcity and crop water productivity separately (Hoekstra and Mekonnen 2011, 2012; Jaramillo and Destouni, 2015; Zhao et al., 2015; Ashraf Vaghefi et al., 2017; Sun et al., 2017). Hoekstra and Mekonnen (2012) has quantified and mapped the water footprint of humanity with high spatial resolution and found that agricultural production accounted for almost 92% of global WF footprint during 1996–2005 (Hoekstra and Mekonnen, 2012). Jaramillo et al. (2015) studied the global effects of flow regulation and irrigation on global freshwater conditions and revealed that the two can raise the global water footprint of humanity by approximately 18% (Jaramillo and Destouni, 2015). Hoekstra and Mekonnen (2011) defined the blue water scarcity index as the ratio of blue water footprint to blue water availability, and applied this index in the world's major river basins (Hoekstra and Mekonnen, 2011). They found that the blue water scarcity level in 55% of the basins studied exceeded 100% at least one month of the year, meaning the blue water footprint surpassed available blue water in these study basins. Zhao et al. (2015) used the water scarcity index to investigate impacts of interprovincial virtual water flow on trading provinces' water scarcity, and found the virtual water flow could exacerbate trading provinces' water scarcity level (Zhao et al., 2015). Ashraf Vaghefi et al. (2017) assessed the crop water productivity of irrigated maize and wheat in Karheh River Basin by using a hydrological model and a river basin water allocation model (Ashraf Vaghefi et al., 2017). Their results indicated a close linear relationship between crop water productivity and yield. Sun et al. (2017) explored crop water productivity of wheat in the Hetao irrigation district at the field scale and analyzed the impacts of agricultural and climatic factors on crop water productivity (Sun et al., 2017). Their results showed that crop water productivity was highly sensitive to relative humidity, wind speed, and irrigation efficiency, while less sensitive to sunshine hours and the amount of fertilizers used.

To our knowledge, water footprint, water scarcity, and crop water productivity have not been assessed simultaneously at the county level in large plains over a temporal scale. Such information is urgently needed since the global irrigated agricultural area has nearly tripled from 1900 to 2005 amid growing population, water crisis and food shortage. Assessing them together can show a more comprehensive interrelationship among food production, water consumption, and water scarcity. This will help to construct targeted policies to achieve both food security and water security in irrigated agriculture. Different from most water footprint studies at coarse spatial scales (e.g., global and national scales) or focused on geographic units (e.g., 5' × 5′ or 30' × 30′ grid), a study at the county level helps to better understand and manage water conservation and food production because much of agricultural planning and water management (e.g., sown area, planned total crop yield, and permits of water use) is done at the county level in countries such as China, India, and Japan.

To fill this knowledge gap, we chose the North China Plain (NCP), with 207 counties, as a demonstration for integrated assessment. The NCP is the national agricultural base and main grain production area in China. The region includes the plain of Beijing, Tianjin City, Hebei Province, and part of Henan and Shandong provinces with 133 million people (Zhang et al., 2012). Approximately 80% of the seeded areas of all crops are grain areas, 96% of which are planted with winter wheat and summer maize (Wang et al., 2001). From 1986 to 2010, the total wheat production and maize production in the NCP had increased from 1.58 and 1.07 to 2.49 and 2.97 million tons, respectively. While the NCP needs water for agriculture, the available freshwater per capita annually in the plain – 302 m³ per year (Zhang et al., 2011) – is less than 1/24 of the global average. This is far below the international standard of freshwater resource shortage with the 1000 m³ threshold (Kang et al., 2013). Using such limited water resources to support large amounts of agricultural production and socioeconomic development is a great challenge, implicating significant impacts on national food security, water security, and sustainable development. Many policies and technology investments have been applied in the NCP to solve the water crisis and ensure sustainable water use for food production, but the outcome has not been assessed comprehensively. Exploring this problem in the NCP can have implications for not only China, but also other irrigated areas worldwide.

The aim of this study was to assess the water footprint, water scarcity and crop water productivity of irrigated agriculture at the county level in the NCP from 1986 to 2010. We calculated the blue, green, and grey water footprint to illustrate the dynamics of total water footprint (WF_total) in the whole NCP; applied the water scarcity index to study the impacts of water consumption from irrigated agriculture on water scarcity in each county; and measured the grain yield per unit water use to represent crop water productivity (Mekonnen and Hoekstra, 2011).