A lack of high-density rootzone soil moisture (θ_RZ) observations limits the estimation of continental-scale, space-time contiguous θ_RZ dynamics. We derive a proxy of daily θ_RZ dynamics — active rootzone degree of saturation (S_RZ) — by recursive low-pass (LP) filtering of surface soil moisture (θ_S) within a terrestrial water-energy coupling (WEC) framework. We estimate the LP filter parameters and WEC thresholds for the piecewise-linear coupling between S_RZ and evaporative fraction (EF) at remote sensing and field scale over the Contiguous U.S. We use θ_S from the Soil Moisture Active-Passive (SMAP) satellite and 218 in-situ stations, with EF from the Moderate Resolution Imaging Spectroradiometer. The estimated S_RZ compares well against SMAP Level-4 estimates and in-situ θ_RZ, at the corresponding scale. The instantaneous hydrologic state (S_RZ) vis-à-vis the WEC thresholds is proposed as a rootzone soil moisture stress index (SMS_RZ) for near-real-time operational agricultural drought monitoring and agrees well with established drought metrics.

中文翻译：

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使用陆地水-能量耦合的根区土壤湿度动态


缺乏高密度根区土壤湿度 ( θ _RZ ) 观测限制了大陆尺度、时空连续θ _RZ动力学的估计。我们通过在陆地水-能量耦合 (WEC) 框架内对表面土壤湿度 ( θ _S ) 进行递归低通 (LP) 过滤，得出每日θ _RZ动态的代理——活跃根区饱和度 ( S _RZ )。我们估计了美国本土遥感和现场尺度上S _RZ与蒸发分数 (EF) 之间分段线性耦合的 LP 滤波器参数和 WEC 阈值。我们使用来自土壤湿度主动-被动 (SMAP) 卫星的θ _S和218 个现场站，采用中分辨率成像光谱仪的 EF。估计的S _RZ与相应规模的 SMAP Level-4 估计值和原位θ _RZ进行了很好的比较。相对于 WEC 阈值的瞬时水文状态 ( S _RZ ) 被提议作为近实时农业干旱监测的根区土壤水分胁迫指数 (SMS _RZ )，并且与既定的干旱指标非常吻合。