Healthy evaluation of farmland water-cycle in a typical irrigated area of North China Plain
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Abstract:
With the rapid increase of population,agricultural water demand has increased largely,which resulted in the continuous construction of irrigation and water conservancy projects.The effect of artificial drive force on farmland water cycle has become more and more prominent,especially in the main grain-producing areas such as the North China Plain,which led to the "nature-society" duality of the farmland water cycle in the irrigated areas.In past years,the irrigation managers only focused on human living and economic benefits,while ignored the natural law and farmland sustainability,caused groundwater over-pumping and ecological environment deterioration,then influenced the high-quality agricultural production in the irrigated area.Thus,to solve the above problems,it is crucial to systematically illustrate the farmland water-cycle "health" and scientifically "diagnose" the related "symptoms". Based on the analysis on the structure and the corresponding health conception of farmland watercycle in irrigation areas,the evaluation index system of farmland watercycle health including four dimensions (water source,water transporting,water consumption,and water withdrawal & drainage) and fifteen indexes were established,according to the selection principle of Analytic Hierarchy Process.The indexes' weight through the combined Analytic Hierarchy Process-Entropy Weight Method were calculated to improve the corresponding objectivity.The threshold values of different health grades in the evaluation index system of farmland water-cycle were set according to the relevant national standards and reference to the related researches.Junliu irrigated area of Wei county,Hebei province was selected as the typical one of the North China Plain.The health of regional farmland water-cycle from 2010 to 2019 was evaluated through comprehensive index method and modified grey correlation analysis,respectively. The index evaluation results show that:the water quality,non-point water pollution of fertilizer and pesticide,and utilization coefficient of irrigation water are mostly "ill";the indexes such as water source diversity,the leakage proportion of canal irrigation water,the piping proportion of field irrigation water,the high-efficiency proportion of water-saving irrigation and reasonableness of planting structure have improved year by year in recent years.The total number of "normal" and healthier grades increased from four in 2010 to nine in 2019.The dimension evaluation results show that the health of water withdrawal and drainage is the worst and most of all are in "sick";while the health of the water source,water transport,and water consumption was improved year by year.The two comprehensive evaluation results both show that the water cycle in the Junliu irrigation area has been improved gradually in the recent decade.The evaluation results of grey correlation analysis show that the health grades of farmland watercycle are "seriously ill" from 2010 to 2015,then upgraded to "normal" in 2016,and reached a stable grade in 2017 and later maintain "sub-health".The scores of the comprehensive index method range from 2.36 to 3.58,and the corresponding health grade was gradually improved from "sick" in 2010 to "normal" after 2015. It is indicated that the comprehensive health of farmland water-cycle in Junliu irrigation area has gradually improved in the recent ten years due to the integrated management of groundwater over-pumping.The non-point water pollution of fertilizer and pesticide is the critical focus for the irrigation.The comprehensiveness and dimension health trends of grey correlation analysis and comprehensive index method are similar.By contrast,the results of grey correlation analysis are more reasonable as the healthy scores approach the critical value,while the results of the comprehensive index method are relatively objective to the whole trend indication.The results could provide a scientific basis and decision-making reference to the management and high-quality development of irrigated areas in the North China Plain.
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