Factors influencing electricity-to-water conversion metering method for irrigation water consumption in Hebei Plain

Regional grain production in the Hebei Plain relies on groundwater irrigation to maintain high and stable yields. However, numerous irrigating wells are scattered, making it difficult to obtain reliable groundwater abstraction for agricultural irrigation. The electricity-to-water conversion method is an indirect measurement of groundwater pumping. The use of electric energy consumption as a proxy offers a solution to the problems of maintenance and acceptance, as electricity is usually metered for fee collection and metering is well accepted. Moreover, it can be efficient and convenient in measuring groundwater abstraction for agricultural irrigation. Based on the electricity-to-water conversion factors of county-level agricultural irrigation and the monitoring results of groundwater depth, this study analyzed the regional characteristics of the electricity-to-water conversion factor and the correlation between groundwater depth and the conversion factor in the Hebei Plain. The Luancheng Agro-Ecosystem Experimental Station of the Chinese Academy of Sciences, as a typical site, was selected for the irrigation experiment to study the relationship between electricity consumption and groundwater abstraction and analyze the influence of time consumption, irrigation method, and seasonal variation of the electricity-to-water conversion factor. We found that: 1) Under the same depth of groundwater level, the electricity-to-water conversion factors in the piedmont region were higher than those in the mid-eastern region of the Hebei Plain, and with a declining water table, the electricity-to-water conversion factor decreased. For every 10 m decrease in the water table, the electricity-to-water conversion factor of the deep aquifer in the piedmont and mid-eastern regions decreased by 0.42 m³∙kWh⁻¹ and 0.15 m³∙kWh⁻¹, respectively. 2) The results of the irrigation experiment showed that the relationship between electricity consumption and groundwater abstraction was relatively stable, and the fluctuation range of the electricity-to-water conversion factor between different times consuming for one irrigation was 5.7%. The irrigation season from early March to mid-June was affected by the seasonal variation of the groundwater level, and the seasonal variation of the electricity-to-water conversion factor was approximately ±10%. Different irrigation methods, such as pipe irrigation and sprinkler irrigation, had a significant impact on the actual conversion factor, and the efficiency of pipe irrigation was 28.8% higher than that of sprinkler irrigation. 3) The current county-level results for the electricity-to-water conversion factor in the Hebei Plain cannot support the requirements of farmers for irrigation metering, water rights, and water resource tax verification. Seasonal variations in groundwater level, irrigation methods, and non-irrigation electricity consumption should be considered to improve the metering accuracy of groundwater abstraction using electricity as a proxy.