Root zone depth: what is it & why is the default so low?

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Root zone depth: what is it & why is the default so low?

Post by rcoville » Tue Apr 25, 2017 8:01 am

Root Zone depth, also known as the Upper Active Soil Zone, represents the root zone 'storage' area, which evapotranspiration draws water from. It reflects an average for all vegetation types, from small grasses to large trees, so we set the default to represent a shallow area close to the surface.

The acceptable range for that parameter is 0.001 – 1.0 meters, which is intended to capture the wide range and extremes of potential root zone stores. Though some tree roots (tap roots) can grow very deep, most roots of those trees still draw water and nutrients from the first few feet of soil depth, and when averaged with other plant roots we assume the average root zone storage area will not be greater than 1 meter deep.

We're not aware of how sensitive the Hydro model is to the root zone depth parameter at this time. It is likely that it can make a significant difference in model results due to its key role in driving evapotranspiration and influencing infiltration, which can in turn have significant indirect effects on soil moisture, pervious area runoff, and the overall water budget.
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