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Abstract:Changes in irrigation water-use efficiency are related closely to agricultural development. Clarifying the driving factors of irrigation water-use efficiency change at different agricultural development stages is beneficial for buffering the contradiction between the protection of water resources and massive agricultural water consumption. It also has theoretical and application value when it comes to elucidating the driving characteristics of spatial changes in irrigation water-use efficiency observed among the different provinces of China. This paper analyzes driving factors of irrigation water-use change based on a study of literature and a field survey. It selects 21 indices from five aspects of climatic change, resource endowment, economic situation, technological level, and management mode as the system of driving factors for irrigation water-use change. This article then uses statistical data on economic and social development in the 31 provinces of China in 2009, and applies the principal component analysis (PCA) method to extract the main driving factors affecting irrigation water-use efficiency change. After calculation of factor scores, clustering analysis is conducted on the 31 provinces to explore regional differences among the driving factors of irrigation water-use efficiency change. The results show that these can be attributed to the factors of agricultural economic development, water-saving irrigation technology, water resource endowment, and dissipation. The 31 provinces can be divided into five types: agricultural economy strong driving type; agricultural economy dominant type; industrial economy dominant type; agriculture strong development type; and coordinated driving type. In highly agricultural provinces, mature irrigation district management and water-saving measures influence the efficiency of irrigation water-use, making these strong positive driving factors. In highly industrial provinces, changes in irrigation water-use efficiency are mainly driven by economic development and structural adjustment, making these weak driving factors.

This paper introduces an integrated approach to find out the major factors influencing efficiency of irrigation water use in China. It combines multiple stepwise regression (MSR) and principal component analysis (PCA) to obtain more realistic results. In real world case studies, classical linear regression model often involves too many explanatory variables and the linear correlation issue among variables cannot be eliminated. Linearly correlated variables will cause the invalidity of the factor analysis results. To overcome this issue and reduce the number of the variables, PCA technique has been used combining with MSR. As such, the irrigation water use status in China was analyzed to find out the five major factors that have significant impacts on irrigation water use efficiency. To illustrate the performance of the proposed approach, the calculation based on real data was conducted and the results were shown in this paper.

Jiangsu is a major province located in the east of China, consuming a large amount of water resources. It is considered that improving the comprehensive water use efficiency has an important significance to achieve sustainable development of the economy in Jiangsu. Through extensive literature research and investigation of Jiangsu Province, this paper establishes comprehensive water use efficiency index system using water consumption per ten thousand dollar gross domestic product (WC/$10 4 GDP) as the research target. In the index system, resource factors such as surface water resources (SW), groundwater resources (GW), precipitation (PT), water resources per capita (PW), water consumption per capita (PC) and irrigation area per capita (PI) cannot be artificially altered. Furthermore, the variation amplitude of resource factors is very small. It shows that the linear regression model is not suitable to analyze the resource factors by changing the independent variables. In view of this situation, this paper introduces impulse response function on the basis of vector autoregressive model (VAR) to investigate the intrinsic link between resource factors and WC/$10 4 GDP in Jiangsu Province. The results show that resource factors have a great impact on WC/$10 4 GDP in Jiangsu, and the per capita water resources (PW) has the most significant impact.

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In this paper, an experimental study has been conducted to monitor the productivity of a single-slope active solar still with three lenses and one mirror. The lenses and the mirror were proposed to be attached to a basin-type single-slope active solar still because of their concentration effect for sunlight. After 24-hour performance monitoring, a higher yield was observed in the new style of solar still as compared with the conventional single-slope still. The lenses refract and aggregate the sunlight from three side walls, and one mirror set on the back of the evaporator can avoid sunlight loss. Model-3 with three lenses produced about a 21.03% yield increment, and an extra 8.77% yield was observed by adding one mirror in Model-4. The yield of the proposed solar still could reach the maximum freshwater production through Model-4 (adding three lenses and one mirror) of 0.8 kg/m2.d on 1/8/2016. Compared with the traditional still, there was a 29.8% increment in yield through Model-4 at 0.15 m water depth, and the production reached its peak at about 16:00.

In order to reasonably use solar energy to solve problems such as land desertification and soil salinization in Southern Xinjiang, this paper proposes a system combining photothermal and flash evaporation technologies, which use local saline water for desalination treatment to achieve secondary utilization of water resources. Firstly, we introduce the whole system of the photovoltaic desalination plant. As an important heat-collecting element of the system, the solar tube is the key to whether this plant can work efficiently. Then, we carry out the detection and theoretical derivation of data along the tube. We establish a two-phase flow model of saline water in the tube, considering convective heat transfer, and define the formula of the heat collecting efficiency factor. Finally, based on iterative calculation, the temperature trend of the tube and the change law of the two-phase flow are obtained, and the ecological and economic benefits and energy efficiency of the system are analyzed.

In this paper, a dome slope single basin solar still for water treatment and desalination is presented. This new solar still device is based on installing a dome slope cover on the walls of the solar still. The main objective of such still is to concentrate more sunrays at the still's bottom basin, through the increased area of dome glass cover. Experiments are conducted under the climate conditions in Hangzhou city, China, for testing the operational performance of dome slope type solar still and the fourfold slope still, so as to make a comparative analysis between them. Assessment of the dome slope still's feasibility is performed based on energy, exergy, exergoeconomic, and enviroeconomic methodologies, as well as energy payback time. Results show that the productivity of dome slope still is 36% higher than that of fourfold slope still, and dome slope solar still enhances the average hourly energy efficiency by 34%. Due to the higher energy and exergy outputs of dome slope solar still throughout its lifetime, the novel solar still proposed in this study mitigates more CO2 compared to the fourfold slope still. Overall, incorporation dome slope cover with the still is found promising in terms of freshwater yield, cost, and energy payback time compared to conventional one. The dome slope single basin solar still appears to be effective from exergoeconomic, exergoenvironmental parameters analysis.