Climate change is currently one of the most critical issues in watershed management, and typical paddy systems should be addressed by watershed modeling approach in paddy-dominant landscapes. This study is designed to evaluate and enhance the watershed modeling approach currently used to characterize the impacts of climate change on hydrologic and water quality responses while considering a paddy environment. APEX-paddy, which is a newly developed and modified APEX (Agricultural Policy/Environmental eXtender) model for paddy ecosystems, was coupled with SWAT (Soil and Water Assessment Tool) model to take advantage of the strengths of the two models. The resulting hybrid model, SWAPX, was calibrated and validated using observed data from 2008 to 2017 for two sites in the study watershed. Compared to SWAT, the accuracy of SWAPX was improved, showing statistically better results in the downstream including more paddy field areas. Ten GCMs were selected, and the characteristics of these GCMs were evaluated to assess the impacts of climate change scenarios. When applying the climate change scenarios to the SWAPX model, the results indicated that the future streamflow would increase due to increased rainfall. The results also showed that total nitrogen (T-N) loads would increase rapidly in the near future, then decrease gradually through the 2090s (2091–2100). T-N load was affected by the characteristics of rainfall patterns (e.g., daily maximum rainfall and rainfall intensity) occurring in various GCMs. This approach will be helpful for decision-makers in adapting to climate change and evaluating Best management practices (BMP) for paddy-dominant watersheds.

中文翻译：

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使用APEX-Paddy和SWAT耦合模型评估气候变化对水文和总氮负荷的影响

气候变化目前是流域管理中最关键的问题之一，典型的稻田系统应通过以稻田为主的景观中的分水岭建模方法来解决。这项研究旨在评估和增强目前使用的分水岭建模方法，该方法用于表征在考虑稻田环境的同时气候变化对水文和水质响应的影响。APEX-paddy是一种新开发和修改的水稻生态系统的APEX（农业政策/环境扩展）模型，并与SWAT（土壤和水评估工具）模型结合使用，以利用这两种模型的优势。使用研究分水岭中两个地点从2008年至2017年的观测数据对所得混合模型SWAPX进行了校准和验证。与SWAT相比，SWAPX的准确性有所提高，在下游（包括更多的稻田面积）显示出统计上更好的结果。选择了十个GCM，并评估了这些GCM的特征以评估气候变化情景的影响。将气候变化情景应用于SWAPX模型时，结果表明，由于降雨增加，未来的流量将增加。结果还表明，总氮（TN）负荷将在不久的将来迅速增加，然后在2090年代（2091-2100年）逐渐减少。TN负荷受各种GCM中出现的降雨模式特征（例如，每日最大降雨和降雨强度）的影响。这种方法将有助于决策者适应气候变化并评估以稻田为主的流域的最佳管理实践（BMP）。