Sustainable Water Use in Arid Agricultural Areas Based on System Dynamics and Water Footprint: a Case Study of Zhangjiakou City, China
The water resource is an indispensable natural capital for human production and life. On the one hand, insufficient water resources and uneven temporal and spatial distribution in arid agricultural areas are the objective reasons for restricting social and economic development and fragile ecological...
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|Summary:||The water resource is an indispensable natural capital for human production and life. On the one hand, insufficient water resources and uneven temporal and spatial distribution in arid agricultural areas are the objective reasons for restricting social and economic development and fragile ecological environment. On the other hand, socio-economic development occupies a large amount of ecological water, especially the unscientific planning and unreasonable expansion of irrigated agriculture, which makes a large amount of water wasted. Therefore, in this study, Zhangjiakou, China, a city with less than 400 m3 of water per capita per year, was taken as a case study area to explore the sustainable use of water in arid agricultural areas from the perspective of blue water (surface water and groundwater) and green water (soil water). First, a complex system dynamics model, reflecting the relationships between the water resources subsystem and other socioeconomic subsystems in Zhangjiakou City, was established using Vensim PLE to simulate water demand (2015-2035) in four designed alternative development scenarios: the Current Development Scenario (CDS), the Economic Priority Scenario (EPS), the Water-saving Priority Scenario (WPS), and the Balanced Development Scenarios (BDS). Secondly, with the help of CropWat 8.0, the water footprint and its spatiotemporal characteristics and variations of the main crops in Zhangjiakou City for 2005, 2010, and 2015 were estimated. Furthermore, an in-depth analysis of blue water, green water, and food productivity and economic benefits of water footprint was further investigated by introducing three new indicators, i.e., green water footprint occupancy rate, blue water footprint deficit, and virtual water consumption per GDP. Finally, from the perspective of the ecological zone, the spatiotemporal matching characteristics of agricultural water footprint and socioeconomic factors were analyzed using the Gini coefficient and imbalance index. The main findings are as follows:
The variables related to irrigation farmland are the main driving factors of water demand, especially the area and the average water consumption of irrigated land. Therefore, reducing the area of irrigated farmland and improving the efficiency of agricultural irrigation water will be the main direction of water-saving in Zhangjiakou City. But it is vital to consider various factors, e.g., agricultural GDP and farmers’ income, to determine the degree of reduction of irrigation area. Besides, in the four development scenarios, regardless of which development model is chosen, the water demand per ten thousand yuan GDP will eventually fall to around 20 m3 in 2035. Therefore, reducing water demand only by slowing down economic growth cannot improve the efficiency of water use, and even result in inefficiency of water supply capacity. Zhangjiakou City should adopt a dynamic and efficient water-saving model that not only sustains regional socio-economic development but also protects ecological security in the whole Beijing-Tianjin-Hebei region.
The total water footprint requirement of Zhangjiakou City increased from 1.671 billion m3 in 2005 to 1.852 billion m3 in 2015, of which the ratio of green water to blue water was around two. The total water footprint requirement in the counties of the mountainous Bashang area is lower than those of the Baxia area, and the gap between them was further expanding. The green water footprint occupancy rate in counties of the Bashang area was 43%-49%, with an average of 44%, while it was 51%-59% in counties of the Baxia area, with an average of 54%. The highest green water footprint occupancy rate in a year was from May to August, at 58%-83%. In terms of blue water footprint deficit, in general, it was lower in the Bashang area than in the Baxia area. The changing trends in food production and economic benefits of water footprint were not always the same. Therefore, it is necessary to consider them simultaneously when developing policies from the perspective of water footprint.
The agricultural water footprint of Zhangjiakou City increased from 3.61billion m3 in 2005 to 5.30 billion m3 in 2015, an increase of 1.69 billion m3, of which the water footprint of animal products increased by 1.59 billion m3. Therefore, in addition to continuing to optimize the planting structure, implement efficient water-saving irrigation measures, and control the water footprint of crops, the government needs to strictly prohibit overload grazing and develop modern animal husbandry to reduce the water footprint of animal products, especially in counties of high-altitude ecological zones I, II and IV. The Gini coefficient and the imbalance index of agricultural water footprint and socioeconomic factors indicate that the spatial distribution of agricultural water footprint and planting area, population, agricultural GDP was relatively balanced, but there were still some significant differences. It means that the adjustment of the agricultural structure in each county requires a comprehensive consideration of multiple socioeconomic factors.|
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