Have a cordial greeting, I am doing a job in Colombia with the annual water yield model, for the calculation of the Z parameter, the equation of the user guide must be applied. I have several doubts regarding the obtaining of the AWC variable and the formula, 1) the raster of the minimum of the effective depth of the soil, it would be to obtain a raster with only the minimum value. 2) the variable depth of the roots, a raster must be obtained since they are values in a table. 3) the equation of the user guide of the AWC variable, the calculation process is through only rasters, with the ARCgis tool.
I’m not exactly sure what your questions are, but perhaps it would help to see more of a step-by-step process than what is currently included in the User Guide?
1/ Create a root depth raster by mapping the root_depth column of the biophysical table to your land use/land cover (LULC) raster.
2/ Use a GIS Raster Calculator or specific math function to calculate the minimum of the root depth raster (from step 1) and the soil depth raster you’re using as a model input.
3/ Calculate AWC using the equation in Appendix 1 of the User Guide, using the output of step 2 and the PAWC raster you’re using as a model input.
4/ Determine the average (mean) value of the AWC raster calculated in step 3, and the average (mean) value of the annual precipitation raster you’re using as a model input. These will be single number values, not rasters.
5/ Use the average values determined in step 4 to calculate Z. You’ll need to look at the referenced papers to help determine ω.
The question would be, should I create a root depth raster of the biophysical table, then do the calculation to obtain the minimum of the 2 rasters, …?? and finally apply the true equations…
I elaborated the two rasters, the root depth raster and the effective soil depth raster, I used the minimum function to obtain two rasters, when performing the operation between the three rasters the result is not very different from the raster of PAWC, then I use a function in Arcgis to obtain the raster statistics, the mean is a value of 0.884 and the total value is 14085, the values obtained are not very consistent with the values I need for the equation, the doubt I don’t know what I’m doing wrong…
I just noticed that I made a mistake in the steps I outlined previously. Step 3 should be:
3/ Calculate AWC using the equation in Appendix 1 of the User Guide, using the output of step 2 and the PAWC raster you’re using as a model input.
Previously it said to use the output of step 1. I’ve corrected this in my post.
The resulting AWC raster should be noticeably different than PAWC, since you’re multiplying the PAWC raster by the minimum (soil depth, root depth) raster that you calculated, and those minimum values are probably large, since they’re in millimeters.
If I do this same process with the sample data that’s provided for the Annual Water Yield model, the different layers have values as shown below, and the map shows the AWC raster that is created:
The mean value for awc.tif in this case is 137.73, and the mean precipitation value for the sample data is 1494.66. These values would then be used in the Z equation.
hola @swolny
I was searching the internet and the only thing I found was an arcgis function to obtain the minimum, but I did not obtain the required results, since I obtained a raster with the value of 1, if you could tell me how are the steps to obtain the minimum, with arcgis using the calculator or another method will be grateful, attach the image of the anointing you use
This says: For each pixel, if soil_depth.tif is less than root_depth.tif, write the value of soil_depth.tif to the output raster; otherwise, root_depth.tif is less than soil_depth.tif, so write the value of root_depth.tif to the output raster. The result is a raster with the minimum value for each pixel.
