定义¹

A top-down approach captures an envelope of the possible based on empirical relationships and has advantages including overall simplicity, obtainable input data, and transparent propagation of error. However, catchment scale top-down models may not be able to explain the impact of local scale changes in catchment management.
重点：基于经验关系的，整体间接性

A bottom-up approach integrates biophysical process understanding, often at point or paddock level, enabling explicit representation of management levers (e.g. management options available to a farmer), and allows prediction of spatial response surfaces .
重点：考虑区域和点尺度异质性的，纵向和侧向水流的

应用²

本研究提出了陆地水储量变化的“自上而下”(基于重力卫星观测)和“自下而上”(基于冰川、湖泊、土壤和地下水储量组分变化加和)反演方法，发现GRACE JPL Mascons水储量反演结果，可以实现青藏高原大部分流域“自上而下”和“自下而上”估算结果的闭合，具有更高的可靠度。

参考：

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1. https://www.researchgate.net/publication/255662679_Comparison_of_Top-Down_and_Bottom-Up_Models_for_Simulation_of_Water_Balance_as_affected_by_Seasonality_Vegetation_Type_and_Spatial_Land_Use ↩︎

2. https://mp.weixin.qq.com/s/CJCf6Ov3EOI1qmUXoefPXg
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