Simulating and assessing the effects of seasonal fallow schemes on the water-food-energy nexus in a shallow groundwater-fed plain of the Haihe River basin of China

Abstract

The increasing dependency on groundwater, especially in irrigated regions, has highlighted the notable place of groundwater resources within the water-food-energy nexus (WFEN). This role is particularly relevant in the Haihe River basin of China, a globally representative area that is experiencing rapid aquifer depletion. The winter wheat (Triticum aestivum L.) fallow strategy may have the potential to limit withdrawal in this region. Based on information from multiple sources, this paper proposed six kinds of fallow schemes—under the same triple-cropping system consisting of winter wheat and summer maize (Zea mays L.) followed by fallow and summer maize in two years (WW–SM/F–SM) but with different irrigation schemes—as scenarios to conduct detailed simulation by a modified Soil and Water Assessment Tool (SWAT) model. Then, the water balance components of the shallow aquifer and soil profile (2 m) under different scenarios were analyzed to quantify the variations in hydrological processes caused by changes in cropping system and pumping intensity. Furthermore, through 17 indices that could quantitatively describe the changes related to the WFEN, the effects of seasonal fallow schemes on shallow groundwater drawdown mitigation, grain yield reduction, and energy consumption savings were evaluated. Based on these evaluation outcomes, linear programming was used to optimize the fallow schemes at the subbasin scale. As a result, to satisfy the constraint of stopping groundwater drawdown as well as improving water and energy productivities, the minimum reduction in the annual average winter wheat yield would be 55% compared with the basic scenario, while the summer maize yield would remain basically stable. Under the optimized fallow scheme pattern, 66% of the well-irrigated cropland should adopt the WW–SM/F–SM system with two irrigation applications for winter wheat and a rain-fed scheme for summer maize; additionally, 24% of the well-irrigated cropland should adopt the WW–SM/F–SM system with one irrigation application for winter wheat and a rain-fed scheme for summer maize, and the recommended fallow schemes for the other 10% of well-irrigated cropland varied spatially. Compared to the basic scenario, the optimized fallow scheme pattern could decrease shallow groundwater exploitation by 36.5 × 108 m3 a−1 (i.e., to realize shallow groundwater equilibrium), reduce the diesel consumption of agricultural machines and electricity consumption of pumping wells by 32% and 90%, respectively, and save energy costs by approximately 873 yuan ha−1. These results could provide a quantitative reference for policy-making in this watershed and serve as a typical case for similar areas that wish to implement fallow strategies to achieve groundwater sustainability.