Spatiotemporal Patterns of Crop Irrigation Water Requirements in the Heihe River Basin, China

Abstract

Abstract:Agricultural expansion, population growth, rapid urbanization, and climate change have all significantly impacted global water supply and demand and have led to a number of negative consequences including ecological degradation and decreases in biodiversity, especially in arid and semi-arid areas. The agricultural sector consumes the most water globally; crop irrigation alone uses up more than 80% of available agricultural water. Thus, to maintain sustainable development of the global economy and ecosystems, it is crucial to effectively manage crop irrigation water. We focus on the arid and semi-arid Heihe River Basin (HRB), China, as a case study in this paper, extracting spatiotemporal information on the distribution of crop planting using multi-temporal Thematic Mapper and Enhanced Thematic Mapper Plus (TM/ETM+) remote sensing (RS) images. We estimate the spatiotemporal crop irrigation water requirements (IWR c ) using the Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith method and reveal variations in IWR c . We also analyze the impact of changes in crop planting structure on IWR c and discuss strategies for the rational allocation of irrigation water as well as policies to alleviate imbalance between water supply and demand. The results of this study show that effective rainfall (ER) decreases upstream-to-downstream within the HRB, while crop evapotranspiration under standard conditions (ET c ) increases, leading to increasing spatial variation in IWR c from zero up to 150 mm and between 300 and 450 mm. Data show that between 2007 and 2012, annual mean ER decreased from 139.49 to 106.29 mm, while annual mean ET c increased from 483.87 to 500.38 mm, and annual mean IWR c increased from 339.95 to 370.11 mm. Data show that monthly mean IWR c initially increased before decreasing in concert with crop growth. The largest values for this index were recorded during the month of June; results show that IWR c for May and June decreased by 8.14 and 11.67 mm, respectively, while values for July increased by 5.75 mm between 2007 and 2012. These variations have helped to ease the temporal imbalance between water supply and demand. Mean IWR c values for oilseed rape, corn, barley, and other crops all increased over the study period, from 208. 43, 349.35, 229.26, and 352.85 mm, respectively, in 2007, to 241.81, 393.10, 251.17, and 378.86 mm, respectively, in 2012. At the same time, the mean IWR c of wheat decreased from 281.53 mm in 2007 to 266.69 mm in 2012. Mainly because of changes in planting structure, the total IWR c for the HRB in 2012 reached 2692.58 × 10 6 m 3 , an increase of 332.16 × 10 6 m 3 (14.07%) compared to 2007. Data show that 23.11% (76.77 × 10 6 m 3 ) of this increase is due to crop transfers, while the remaining 76.89% (255.39 × 10 6 m 3 ) is the result of the rapid expansion of cultivated land. Thus, to maintain both the sustainable development and ecological security of the HRB, it is crucial to efficiently manage and utilize agricultural water in light of spat...

Response of net primary production to land use and climate changes in the middle‐reaches of the Heihe River Basin

“…Moreover, the planting adjustment of wheat and barley (C3 crop with relatively low NPP) into corn (C4 crop with relatively high NPP) led to a NPP increase in the central agricultural oasis. Due to the higher accumulated temperature and more convenient irrigation in the central MHRB (Liu, Song, & Deng, ), this area had a higher increase in cropland NPP than high‐altitude mountainous. Meanwhile, influenced by the Grain‐for‐Green project, farmers tended to returned low‐yield cropland to forested areas and grassland, resulting in decreased LUI but increased NPP in the marginal agricultural oasis and mountainous areas of MHRB.…”

“…The climate in MHRB is a typical temperate continental climate, with an average annual rainfall of 100-250 mm (70% of the precipitation are concentrated in June-August), an average annual temperature of 6-8°C, an annual sunshine duration of over 3,000 hr, and an annual potential evapotranspiration of 1,600-2,400 mm (Liu, Song, & Deng, 2016;Song, Liu, Deng, Zhang, & Han, 2018). Water is the key factor constraining the development of the ecosystem and human society in the MHRB, in which agriculture consumes more than 90% of the water resources (Liu, Song, & Deng, 2017). Land use and climate changes affect the supply and distribution of water resources, resulting in a change in the ecosystem state of MHRB (Song, Liu, Arowolo, Zhang, & Xu, 2018a;Tan & Zheng, 2017).…”

“…Changes in temperature and precipitation have enhanced snowmelt, which have led to a slight increase in available water resources of MHRB. However, F I G U R E 1 Location of the middlereaches of the Heihe River Basin the increase in agricultural and urban water consumption has led to ecological water reduction and ecosystem degradation (Liu, Song, & Deng, 2017;Song, Liu, Arowolo et al, 2018a).…”

Estimation of Irrigation Water Demand and Economic Returns of Water in Zhangye Basin

“…Water 2018, 10, 19 4 of 21 broad, flat plains suitable for irrigated agriculture, in which water use accounts for the majority of total water consumption in the river basin (about 94%), which is located in the center of the "One Belt and One Road" and "Silk Roads" economic belts [44]. The major economic sector in the midstream that uses water in the HRB is irrigation agriculture, in which spring-wheat and maize are the main crop types.…”

“…Surface water supplies about 67% of the irrigation water and the rest comes from groundwater (Zhangye Water Authority). Due to the lack of rainfall and runoff water, groundwater is used excessively in ZB for irrigation, which results in rapid increase of the depth of the ground water there at a rate of 0.5-1.8 m each year [44,48]. However, there is an irrigation water balance, because there are strong interactions among surface, ground, river, and irrigation water [49].…”