Calculate soil water storage changes over time from soil water content

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madegeogr
Posts: 4
Joined: Wed Mar 13, 2019 8:17 pm
Location: Cyprus

Calculate soil water storage changes over time from soil water content

Post by madegeogr » Wed Sep 04, 2019 1:56 pm

Hi,
I have read in literature that HYDRUS-1D is able to estimate the soil water storage changes over time calculated from changes in soil water
content. I have a confusion on this manner.
My understanding is that we can think of the volumetric water content of soil either at each location using Richard's equation (denoted as θ) or by simply calculated the total amount of water stored in the soil divided by the amount of dry soil. The latter definition refers to the amount of water stored (denoted as soil water storage) in the soil, with only difference that is normalized based on the amount of dry soil.
Based on the above, my questions are:
1) How is volumetric water content of soil, based on the latter definition, differs from the soil water storage in Hydrus?
2) How can we calculate the soil water storage from volumetric water content of the soil, if they are not assumed equal?
3) How can we calculate water holding capacity in Hydrus?

Kostas

Jirka
Posts: 4733
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Calculate soil water storage changes over time from soil water content

Post by Jirka » Sat Sep 07, 2019 2:52 pm

HYDRUS uses volumetric water content, i.e., volume of water over volume of soil. Soil water storage is a simple integral of the volumetric water content over depth and thus its units are the length units (e.g., cm or m). If you want to have different units for water storage, then you need to make conversions yourself.

HYDRUS does not recognize the term water holding capacity as this term is not related to the numerical solution of the Richards equation, but is related to the retention curve. Since water holding capacity is the total amount of water a soil can hold at field capacity, you can calculate it from the information in the Check.out, where HYDRUS prints retention data in a tabular form.

J.

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