In this study, we use the Community Land Model Version 5 (CLM5) to investigate how irrigation modulates hydrologic and biogeochemical dynamics in the Upper Columbia‐Priest Rapids (UCPR) watershed, a typical semiarid watershed located in the northwestern United States dominated by cropland. To our knowledge, this constitutes the first application of CLM5 with landscape heterogeneity fully resolved over a watershed. The model is calibrated and evaluated against flux measurements from an AmeriFlux site and the Moderate Resolution Imaging Spectroradiometer (MODIS) products. Two numerical experiments (i.e., irrigated and rainfed) are performed at hyperresolution (~1 km) over the period of 2010–2018, accounting for realistic crop types and management practices. Our results show that irrigation fundamentally alters hydrologic and biogeochemical dynamics of the watershed. By adding 79.6 mm year⁻¹ water in addition to the mean annual precipitation of 204.0 mm year⁻¹, irrigation leads to increases in evapotranspiration and runoff, accompanied by shallower groundwater table depths. Increases in crop productivity in response to irrigation result in more carbon storage in the watershed, and drastically large seasonal fluctuations in soil organic carbon in response to changes in soil temperature and moisture. Irrigation also intensifies the rate of denitrification and mineralization during the growing season, enhancing the interactions between soil mineral nitrogen, the atmosphere, and freshwater systems. Our study demonstrates the potential of CLM5 as an effective tool for understanding hydrological and biogeochemical dynamics in highly managed semiarid watersheds.

中文翻译：

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西北太平洋半干旱流域灌溉对水，碳和氮预算的影响：模型研究

在这项研究中，我们使用社区土地模型第5版（CLM5）来研究灌溉如何调节上哥伦比亚-普里斯特急流（UCPR）流域中的水文和生物地球化学动力学，该流域是位于美国西北部以农田为主的典型半干旱流域。据我们所知，这是CLM5的首次应用，其景观异质性已在分水岭上得到完全解决。根据AmeriFlux站点和中分辨率成像光谱仪（MODIS）产品的通量测量值对模型进行校准和评估。在2010-2018年期间，以超高分辨率（〜1 km）进行了两个数值试验（即灌溉和雨养），这些试验考虑了现实的作物类型和管理实践。我们的结果表明，灌溉从根本上改变了流域的水文和生物地球化学动力学。每年增加79.6毫米除了年平均降水量为204.0 mm年^-1的-1水以外，灌溉还导致蒸发蒸腾和径流增加，同时地下水位较浅。灌溉带来的农作物生产力的提高导致流域中碳的存储量增加，并且随着土壤温度和湿度的变化，土壤有机碳的季节性波动极大。灌溉还增加了生长期的反硝化作用和矿化速率，增强了土壤矿质氮，大气与淡水系统之间的相互作用。我们的研究表明CLM5作为了解高度管理的半干旱流域中水文和生物地球化学动力学的有效工具的潜力。