Account for hillslope aspect in ET calculations?


#1

I know you guys use Penman Montieth for ET – one of the things it is highly sensitive to is solar radiation – I know you have a setting that is how many hours per day the system sees sunlight, but have you considered integrating the hill aspect into the app/calculations? e.g. we have a steep south facing slope, so the ET will be a lot higher than an equivalent steep north facing slope.

It seems you could probably do some basic map work and have the user drop a pin on each zone and use existing DEMs to try to auto-calculate the slope/aspect.


#2

The DEM can be fine tuned by using different slope aspects mild/moderate/steep as well as shade aspects of the program ie: some shade/ moderate shade/ mostly shade.

I prefer to use MP rotators on slopes or Toro 300 rotors in order to control the dispersion rate as well as avoiding heavy saturation which can result from improperly tuned PGP or PGJ rotors.

Otherwise, drip can be used up to a certain gradient level and multiple GPH emitters can completely fine tune the needs of each plant while allowing current ET values to maintain control.

Obviously, if a hillside is half sun and half shade or even mixed gradients, you will need to fine tune the emitters more precision.