Hello, good afternoon. We have been running the SWY model and also the annual WY for some sub-basins, with the same inputs, but we have observed that the AETs differ a lot between both models. In the SWY model, the AET is usually very high for most of the sub-basins analysed. Why are these differences due if they are the same inputs?
Hi @EdithOrozco -
The SWY and AWY models do have some inputs in common, but if you read the User Guide you’ll see that AET is calculated differently between them.
AWY (y en español) is a much simpler model, with inputs on an annual timescale, and there is no routing of water downslope.
SWY (y en español) is more complex, the inputs are given monthly, and the AET calculation does take into account the water moving downslope, some of which is being used by vegetation along the way.
You can see more details about this by checking out the equations in the User Guide. I don’t know of a study that has specifically compared the AET results of these two models, but do know that these two models were developed independently, the AWY model is quite old, SWY more recent. So I also can’t say which one is more “correct” than the other, only that SWY does the extra step of taking into account water flowing into each pixel from upslope, which may contribute additional water to be evapotranspired by the pixel, leading to higher AET values.
~ Stacie