how to integrate soil moisture layers in Noah-MP module

[Ceil]

Dear all,

I am confused about how to calculate the total soil moisture when considering multiple layers.
The stimulated soil moisture has four layers (i.e., 0-10cm; 10-40cm; 40-100cm; 100-200cm) in Noah-MP module. But if we want to get the soil moisture in the layer 0-40cm and 40-200cm, can we directly plus the first two layers and the last two layers, respectively? Or should we do average?

Many thanks!

 

[tslin2]

I think this depends on the unit

 

[SLeGrand]

WRF stores the soil moisture parameter in terms of volumetric soil moisture (the ratio of the volume of water to the unit volume of soil). If you want to combine multiple levels, you'd want to take a weighted sum to account for differences in soil layer thickness.

For example, the Noah-MP soil layers have thicknesses (z) of z1 = 10cm, z2 = 30cm, z3 = 60cm, and z4 = 100cm. They each have their own volumetric soil moisture value of smois1, smois2, smois3, and smois4, respectively. Using your example of combining the first two layers and the bottom two layers, z12 = 40cm and z34 = 160cm.

The combined soil moisture for the top two layers (smois12) would be: smois12 = (z1/z12)*smois1 + (z2/z12)*smois2 = 0.25*smois1 + 0.75*smois2