The input data of annual water yield

Hello, Community! Hope everyone is well!
I am assessing annual water yield ecosystem services in a certain region.

  1. The input data requires the potential evapotranspiration raster data. Is it possible to directly use the annual composited MODIS16 ET data or some other ET products? The PET value is greater than the ET value. Which dataset is better for the assessment of annual water yield?
  2. I found that the depth of water yield in the urban area is larger than in other areas. Is it correct? The reason is precipitation? Because the evapotranspiration in the urban area is no-data or filled value. Also, should do the evapotranspiration values in the urban area as zero or no data?
  3. Are the final outputs largely affected by the scale effect? The input raster data may be different spatial resolutions. Should I make all the data to a united scale (e.g.,1km)?

Thanks a lot.
Looking forward to hearing from you.

Best
Icey

Hi @Icey -

Yes, you may use PET data for Annual Water Yield, the model will calculate actual ET, using PET and the evapotranspiration coefficients you provide for each land cover type.

Using this kind of simple model, we do often see greater water yield in urban areas, mostly due to there being less plants to take up some of the water. So we advise caution when interpreting the results, since it can look like “if we want water, cut down the forest and build a city”, which obviously does not take into account the complexities of infiltration, dry season baseflow, etc, that are more likely to be provided by natural vegetation.

You can provide spatial data with different resolutions, and in the case of Annual Water Yield, the model will resample all of your layers to be the same resolution as your land cover map. So you do not need to make all of the data the same resolution, but personally I usually prefer to, so I know that the resampled rasters look correct.

~ Stacie

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Many thanks @swolny, I know how to continue my work now~

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