Estimation of vegetation evapotranspiration and quantification of virtual water in mining areas

In the ecological restoration of mining reclamation areas, vegetation evapotranspiration plays a crucial role in water resource consumption. The virtual water theory offers a new perspective for water resource management, yet limited research has been conducted on the quantification of virtual water in ecological vegetation within mining areas. This study aims to estimate the evapotranspiration of different vegetation types in a mining reclamation area and quantify their virtual water content and water footprint based on the virtual water theory, providing insights into the optimization of water resource allocation. The study is conducted in the microbial reclamation demonstration base of the mining area, selecting Hippophae rhamnoides, Amorpha fruticosa, and Pinus sylvestris var. mongolica as research subjects. Thermal infrared imaging technology combined with the energy balance equation is employed to calculate vegetation evapotranspiration, while the CROPWAT model is used to estimate vegetation water requirements. Additionally, Hippophae rhamnoides is used as a case study to quantify virtual water and water footprint, analyzing the irrigation water demand, virtual water content, and water use efficiency of different vegetation types. The findings indicate that inoculation treatment significantly increased vegetation evapotranspiration. The highest evapotranspiration is observed in the inoculation area of Pinus sylvestris, reaching 8.17 mm/d. while the lowest is in the Pinus sylvestris var. mongolica control area in 2012 （4.94 mm/d）. The reference crop evapotranspiration in the mining area varied between 2.51-3.29 mm/d from 2012 to 2021, increasing with temperature and wind speed while decreasing with relative humidity. Significant differences in water demand among vegetation types are found, with Hippophae rhamnoides requiring the highest amount of water （7 469.5 mm） and Amorpha fruticosa the lowest （4 619.4 mm）. The virtual water content of Hippophae rhamnoides exhibits a rising and then declining trend, peaking in 2020 at 17 657.60 m³/t, with blue water footprint significantly surpassing green water footprint. Moreover, the overall water use efficiency in the mining area is low, with a maximum efficiency of only 54.8%, highlighting the urgent need for improved water-saving strategies. This study validates the applicability of the CROPWAT model in assessing water resource consumption of ecological vegetation in mining areas and, for the first time, quantifies the virtual water content and water footprint of vegetation in a mining reclamation site. The findings provide theoretical support for optimizing water resource management in mining ecological restoration. It is recommended to enhance the utilization of green water, optimize irrigation strategies, and introduce drought-resistant vegetation to improve water use efficiency and promote sustainable ecological recovery in mining areas.