Season formula (Water Overlay)

The season fraction and index are variables used for calculating the transpiration factor in the Ground transpiration formula. It uses the configured start date of a Water Overlay and selected months and day of months to determine one of the four configured (seasonal) transpiration factors.

Transpiration month, day of month and corresponding transpiration factor array value:

Month	Day of Month	Transpiration value
March	15	1st
April	15	2nd
July	15	3rth
September	15	4th
October	1	1st

Transpiration factor graphs

The transpiration graphs showing the transpiration factor as a percentage per day. These are based on Table 2.10 Cropfactors of the Gwz2016 book^[1]. The approximated graphs use five control points (see the season table above) per type, such that it can be reduced to four values per year. Values between the control points are obtained by interpolation.

Transpiration factors in the Function Values Table in the editor

Notes

The growth season dates are determined based on western european growth and transpiration graphs of the following crops and plants: grass, corn, potato, beet, grain, orchard and heather.

References

↑ Grondwaterzakboekje, Gwz2016 (Impressed druk en print) ∙ Makkink, Bram Bot (2016) ∙ Page(s): Table 2.10 Gewasfactoren, % van referentiegewasverdamping