The minimum value obtained for water production starts at 0.

[Beipoerdawang]

The minimum value obtained for water production starts at 0. Isn’t it related to evapotranspiration and rainfall? The average annual evapotranspiration in my study area is greater than the average annual rainfall. Also my water yield calculations are missing watersheds, is it because the PAWC calculations are missing watersheds? What should I do if I want to have the watershed information in the results?

[swolny]

Welcome to the forum @Beipoerdawang!

Yes, anywhere there is NoData in your input rasters there will be NoData in the model output rasters. If you want model results in those areas, you’ll need to fill in the NoData holes in your PAWC input layer with estimated values. This topic has been discussed many times on this forum, and I encourage you to search for posts related to missing data in soil layers.

As for water production, if there is more evapotranspiration in a pixel than precipitation, then no water will be produced, it will all be used by the pixel itself, so the output value will be 0.

~ Stacie

[Beipoerdawang]

I would like to ask what value is appropriate to fill in the NoData value (with water) in the PAWC, because my study area has more water.

[Beipoerdawang]

I would like to ask what value is appropriate to fill in the NoData value (with water) in the PAWC, because my study area has more water.

[swolny]

Hi @Beipoerdawang -

I was unsure of what would be a good value to assign to water bodies, so consulted with NatCap scientists and heard this:

PAWC should be set at the maximum in areas where there are water bodies. This implies that there is no limitation in the amount of water available in the soils under the water for plants to use. There probably is very little vegetation in open water bodies, but some areas classified as water could actually have emergent vegetation or be seasonal wetlands, so assuming that they are almost always wet (which should be a safe assumption if they are classified as open water) would imply maximum PAWC.

Also if the amount of water evapotranspired off of each pixel is calculated as a combination of PAWC and Kc, and if Kc is pretty high for water bodies, then having PAWC at the max would mean that all water is available for evapotranspiration (or evaporation, in the case of open water). Which is the case in reality.

So the recommendation is to use the maximum value of 1 for water bodies.

I’ll update the User Guide with this information as well.

~ Stacie