Evaporation is the larger of the results of the following equations
E0 = 290Dw((Dr-Dw)^(1/3))(Ww-Wr)
E0 = 0.0346(pw-pr)
where:
E0 = evaporation from pool, pounds per hour per square foot of exposed surface area
Dw = density of air saturated at water temperature, pounds per cubic foot of dry air
Dr = density of air saturated at air temperature, pounds per cubic foot of dry air
Ww = humidity ratio, air saturated at water temperature, pounds per pound
Wr = humidity ratio, at air temperature, pounds per pound
pw = water-vapor pressure in air, air saturated at water temperature, inches of mercury
pr = water-vapor pressure in air, at air temperature, inches of mercury
The above I got from somewhere to calculate pool evaporation for indoor pools and adpapted it slightly. If you account for rain filling, it actually works quite well for running a fill system. You will of course have to convert the volume measurements, to run on the sprinkler controller, but that should handle the majority of the ground work. I personally had a dedicated pump controller that used those measurements.
Hope it helps a bit.