Quantifying the annual water yield per LULC class

Science, Research & Data
1

Good day! I am using the annual water yield model to analyze the impact of different LULC scenarios on the water yield of a certain watershed. I was wondering if there is a way to utilize the model outputs in order to quantify the annual water yield for each LULC class. Any help is appreciated, thank you.

2

Hello @ccquinon, and welcome to the forum!

If you want to calculate the water yield by LULC class, you just need to use the GIS tool Zonal Statistics to calculate the sum or mean of the water yield result.

~ Stacie

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3

Thank you for the information @swolny !

I tried using zonal statistics with the output\per_pixel\wyield.tif and the LULC map. When I get the sum of the water yield of each LULC class, the total value is greater than the total water yield volume value found in the output\watershed_results_wyield_.csv. I wondering if this is because the total value of the raster is different from the total water yield volume value in the .csv? I would also like to ask if it is accurate to utilize the values from the zonal statistics for the total water yield and the water yield per class even if it is different from the value in the .csv file?

Any help would be very appreciated.

4

Hi @ccquinon -

The units of wyield.tif are millimeters. Did you convert these to volume before comparing them with wyield_vol in the watershed result table?

~ Stacie

5

Good day! After converting the the units of the wyield.tif to cubic meters, the total value becomes less than the wyield_vol found in the watershed result table. Is it alright to use the values of the wyield.tif despite it being different from the volume in the watershed result table? Thank you!

6

Hi @ccquinon -

Would you please describe in more detail how you’re calculating total volume?

The model calculates wyield_vol by taking the mean value within the watershed (wyield_mn in the output watershed table), multiplying it by the area of the watershed, and converting from millimeters to meters:

wyield_mn * watershed area / 1000

I realize this isn’t in the User Guide, so will add it.

~ Stacie

1 Like
7

Good day! I was calculating the total volume by converting the mm to cubic meters because I initially thought that it was cubic mm, but I have realized that that was not the case. Sorry for the inconvenience. Using the formula you have provided I was now able to attain a value that is closer to the volume found in the watershed result table. Thank you!