Ecological-oriented Comprehensive Benefit Evaluation Method Of Water-saving Retrofit In Irrigation District

As the main battlefield of agricultural production,irrigation district is the stabilizer of food security and the ballast of national security.At the same time,the irrigation district is also a large water user.Its water-saving rehabilitation has alleviated the shortage of fresh water resources in China.Under the background of promoting the construction of ecological civilization,the ecological benefits of water-saving rehabilitation in irrigation district have been paid more and more attention.It is urgent to carry out the comprehensive benefit evaluation of water-saving rehabilitation in irrigation district considering ecology.Taking the Yahekou irrigation district as an example,this paper studies the evaluation of water-saving rehabilitation of irrigation district by relevant stakeholders such as application object,management and designer of irrigation district,and analyzes the temporal and spatial evolution laws and main influencing factors such as irrigation water,grain increase,income increase and groundwater depth;Combined with the ecological benefits of water-saving rehabilitation of irrigation district and considering its impact outside the irrigation district,an ecological oriented comprehensive benefit index evaluation system of water-saving rehabilitation of irrigation district is established,and the deficiencies of research at this stage are gradually solved by using optimized cloud model and ecological service value estimation model;In view of the disadvantages that it is difficult to give consideration to the accuracy and uncertainty of the evaluation results,the comprehensive benefits of water-saving rehabilitation in irrigation districts are analyzed layer by layer by coupling the optimization cloud model and the ecological service value estimation model.The main conclusions are as follows:（1）Deconstructs the main single benefits and influencing factors of water-saving retrofit in irrigation district.The canal lining rate is recalculated by replacing the length with area,and the temporal and spatial characteristics and influencing factors of water-saving rehabilitation in irrigation district are analyzed.From 1998 to 2021,the water-saving rehabilitation project of Yahekou irrigation district was promoted from north to south.The quantities from 2007 to 2018accounted for 71.35%of the total quantities.Capital investment is the main influencing factor（r=0.617^*;B=33.712;R²=0.381）.61.75%of farmers,75%of experts and irrigation district managers recognize the water-saving rehabilitation of irrigation district.The annual total water consumption(r=-0.538^**;B=-18.669;R²=0.290),total irrigation grain increase benefit（r=0.784^*;B=3.781 E-3;R²=0.614）,grain increase benefit per unit area（r=0.960^*;B=7.266;R²=0.921）and grain increase benefit per unit water（r=0.886^*;B=5.096E-3;R²=0.786）are significantly affected by the water saving rehabilitation of the irrigation district.From 1998 to2021,the total annual water consumption decreased by 60.74%,and the other three types of benefits increased by 2.19 times,1.91 times and 6.40 times respectively.The water-saving and grain increasing benefits of the water-saving reconstruction project in the irrigation area are obvious,but the impact on the buried depth of groundwater is not significant.（2）The comprehensive benefit evaluation model of water-saving retrofit based on optimized cloud model is constructed.Taking into account the ecological,economic and social benefits,an evaluation system for the comprehensive benefits of water-saving rehabilitation in irrigation district is constructed.The cloud model algorithm is introduced to dynamically adjust the entropy and super entropy in the weighted cloud model,and the traditional cloud model is optimized in combination with shape similarity.While fully considering the ecological benefits and ensuring the evaluation accuracy,the randomness and fuzziness among various index factors are taken into account,A comprehensive effect evaluation model of water-saving rehabilitation based on optimized cloud model algorithm is established.The comprehensive benefit cloud model of water-saving rehabilitation in Yahekou irrigation district is（0.6161,0.1970,0.0919）,which has the highest similarity with grade II"good"（0.625,0.1062,0.01）in the comment cloud model,reaching 0.5012.（3）The comprehensive benefit evaluation method of water-saving retrofit based on ecological service value is reconstructed.Introducing the theory of ecological service value,this paper constructs the comprehensive benefit evaluation model of irrigation district water-saving rehabilitation based on ecological service value,analyzes the main influencing factors of comprehensive benefit,further considers the external benefits of irrigation district water-saving rehabilitation,such as carbon fixation and oxygen supply,improving water quality and so on,and the output evaluation results are easy to understand.The average annual ecological service value generated by the water-saving reconstruction project of the Yahekou irrigation district is about491.75 million yuan,which is 6.20 times of its annual economic cost,and the comprehensive benefit is remarkable.Precipitation,temporal and spatial distribution of precipitation during crop growth period and the progress of water-saving rehabilitation project are important factors affecting the comprehensive benefits of water-saving rehabilitation project in irrigation district.The comprehensive benefit of water-saving rehabilitation project is negatively correlated with the precipitation during crop growth period（r=-0.913^*;B=-0.10;R²=0.833）.（4）A comprehensive benefit evaluation of water-saving retrofit oriented to ecology taking into account accuracy and uncertainty is constructed.Taking the optimized cloud model as the main technical means,the accurate evaluation results obtained based on the ecological service value estimation model are fuzzed.While fully considering the benefits of ecology and inside and outside the irrigation district,the accuracy and uncertainty of the comprehensive evaluation results are taken into account to ensure the authenticity,practicability and objectivity of the evaluation results.Through case study,the comprehensive benefit range generated by the water-saving reconstruction project of the Yahekou irrigation district is about[132.93,95249]million yuan every year,and the reliability of this benefit range is about 68.26%.