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With intensified global warming, accurate quantification of hydrological processes in seasonally frozen regions, particularly with irrigated overwinter crops, is necessary to develop management strategies that promote groundwater conservation. By incorporating a physically based freeze‐thaw cycle module into the Soil and Water Assessment Tool (SWAT‐FT) model, variations of surface hydrology and groundwater dynamics were systematically assessed in North China Plain under three Shared Socioeconomic Pathways during 2041–2070 and 2071–2100 periods between the conventional and improved SWAT models. Compared to the conventional SWAT model, the SWAT‐FT model predicted an increase in soil water content, decrease in irrigation, and an increase in percolation during the growing season of winter wheat. These discrepancies resulted in a 5% higher decline rates of shallow groundwater levels simulated by the SWAT model compared to the SWAT‐FT. Additionally, the SWAT‐FT model projected that the average decline rates of shallow groundwater levels were approximately 0.90 ± 0.16 m yr−1(SSP1‐2.6), 0.60 ± 0.46 m yr−1(SSP2‐4.5), and −0.17 ± 0.53 m yr−1(SSP5‐8.5), respectively, during 2071–2100 compared to the historical period. The SWAT‐FT simulations indicated that the decline rates in shallow groundwater levels were projected to either decrease slowly or potentially increase by the end of the 21st century under the SSP5‐8.5 scenario, potentially achieving equilibrium between shallow groundwater extraction and replenishment. Our study emphasized the importance of considering the freeze‐thaw processes to evaluate groundwater variations more accurately in response to climate change effects in temperate regions with an overwinter crop. As the Earth gets warmer due to climate change, it's important to understand how water behaves in places that have cold winters. This helps us manage our water resources better. We used a computer model called SWAT to study this in North China. We added a special module to the model to simulate the freezing and thawing of water. We looked at how water on the ground's surface and underground might change in different future climate scenarios. We compared the old model to the new one. Both models said that less water would evaporate from the ground, and more would be caught by plants in all scenarios compared to the past. The models were different in how much water evaporated from the ground and moved underground. The new model showed bigger differences during the winter wheat growing season when farmers often water their fields and water goes into the ground. The new model also predicted that the level of groundwater (water underground) might change in different ways based on the climate scenario. Our study shows that understanding how freezing and thawing affect water is important for predicting how groundwater will change because of climate change in places with winter crops.

Nitrogen (N) loss is a significant source of water quality pollution in alluvial watersheds. However, the mechanisms linking N loss and elevated CO2concentration (eCO2) are not well recognized. In this study, we comprehensively calibrated the SWAT model equipped with a dynamic CO2input and response module to investigate the response mechanisms between multiform N losses and eCO2in a representative large‐scale watershed. Results revealed nitrate loss under eCO2exceeding 100% in some upstream zones under the SSP5‐8.5 scenario (P< 0.05) compared to the constant CO2concentration. This was directly related to the great increase in hydrological variables, which were the carriers of N losses, and the intensive inputs of N fertilizer. Results also found that nitrate leaching was greater than the other two processes for future periods, peaking at 309.3%, as compared to the baseline period. The findings suggested reducing fertilizer inputs by 10%–20% was promising, especially for reducing nitrate loss through runoff and leaching by up to 17.7% and 12.2%. This study explored the mechanisms of increased N loss in response to eCO2and provided scientific evidence for early warning and making decisions to improve water quality at a large watershed scale.

Climate change has had a considerable impact on potato production in Agro-Pastoral Ecotone (APE) in North China over the past several decades and it will continue to influence the growth of potato. Thus, understanding the impact of climate change on potato production is critical for future food security in this region. In this study, the calibrated APSIM-Potato model was used to assess the impact of future climate change on potato at Zhangbei (ZB) and Wuchuan (WC) experimental stations. The daily climate data were statistically downscaled from 32 global climate models under two Representative Concentration Pathways (RCP4.5 and RCP8.5). The results showed that potato yield under rainfed condition at ZB site respectively increased by 7.3% and 6.7% in the 2030s, 25.8% and 21.8% in the 2060s and 44.7% and 51.9% in 2090s under RCP4.5 and RCP8.5 scenarios. Potato yield under irrigated condition at WC site increased respectively by 5.5%, 10.0% and 15.1% in the 2030s, 2060s and 2090s under RCP4.5 scenario and by 5.7%, 20.9% and 41.1% under RCP8.5 scenario. Both evapotranspiration and water use efficiency increased under future climate change. Based on the statistical analysis, 70% of the variation in potato yield under rainfed condition at ZB site and 50% of it under irrigated condition at WC site were driven by future climate change. We concluded that rainfed potato yield will be enhanced more by future climate change than irrigation system. Our study filled the knowledge gap in understanding the potential effects of future climate change on potato production under different water management measures, and will be useful in developing adaptable strategies to enhance potato yield in the APE region under future climate change.