A case study on the causes of the paradox of irrigation efficiency in the Tarim River basin
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Abstract:
Agricultural water consumption accounts for over 70% of the world's water consumption. For a long time, promoting water-saving irrigation technology and improving agricultural water efficiency have been regarded as effective methods to reduce agricultural water consumption and alleviate regional water scarcity. However, an increasing number of studies have shown that with the application of water-saving technology and the improvement of water-saving levels, the shortage of water resources worldwide has become even more severe, resulting in the paradox of irrigation efficiency. The emergence of the paradox of irrigation efficiency results from various factors such as hydrology, economy, society, institutions, and management, and the expansion of irrigation area is an important reason for the paradox. Revealing the mechanism of the paradox of irrigation efficiency is the basis for improving water and land resources management in the river basins. Tarim River basin is located in an inland arid area with scarce water resources, and the natural ecology is very fragile. In the recent comprehensive management of the Tarim River basin, nearly half of the investment was spent on water-saving renovation in irrigation areas. However, the expected results were not achieved. The expansion of irrigation area resulted in the widespread phenomenon of "reclaiming land while controlling" and "saving water while consuming water". Under the condition of a certain amount of total water resources, there is a game competition relationship between natural and artificial systems regarding water consumption. Therefore, it is urgent to explore the evolution of water consumption with water use efficiency in water-saving development between natural oasis ecosystems and artificial oasis socio-economic systems.The Tarim River basin, the most apparent contradiction in water and land resources, was taken as an example. The rapid development of water-saving technology from 1990 to 2020 was selected as the study time. Under the conditions of consistent water resources, social economy, and water-saving levels in the basin, two cases was set up, i.e., the actual case with irrigation area expansion and the ideal case with irrigated area maintenance. The basin’s water consumption and water use efficiency varying with the development of water-saving irrigation were analyzed and compared with the two cases. The results show that in the past 30 years, the irrigation water use efficiency of the basin has increased from 0.28 to 0.55, the gross irrigation quota has been reduced by twice, and the water-saving level has been significantly improved. In the actual case, 3.6 billion m3of net water savings have been used to expand irrigation area, resulting in more than doubling of irrigation area and water consumption. The area ratio of artificial and natural oases has changed from 40∶60 to 55∶45, and the water consumption ratio has changed from 4∶6 to 6∶4. The proportion of oasis water consumption to water resources has increased from 72% to 91%, resulting in a severe paradox of irrigation efficiency. In the ideal case, the irrigation water consumption is reduced, the area and water consumption ratio of artificial and natural oases are maintained at around 4∶6, and the proportion of oasis water consumption to water resources is 70%, resulting in an actual water saving of 2.4 billion m3, avoiding the occurrence of the paradox of irrigation efficiency.The emergence of the paradox of irrigation efficiency is the complete result of factors such as great water conditions, water-saving development, planting structure adjustment, and irrigation area expansion. In the past 30 years, the expansion of the irrigation area has played a leading role in the emergence of the paradox of irrigation efficiency in the Tarim River basin. In order to avoid the occurrence of the paradox of irrigation efficiency, it is necessary to manage water resources strictly, adhere to the principle of "water settling land", and promote the balanced development of soil and water resources in arid inland river basins.
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