The value of Ks is calculated on a daily basis as a function of the maximum and actual available soil moisture in the root zone. Ks[t] = S[t]
(1−p)×Smax[t]
if S[t] < (1−p)×Smax[t]
1 Otherwise (2)
where S[t] is the actual available soil moisture at time t (in mm); Smax[t] the maximum available soil water in the root zone, i.e., the available soil water in the root zone when soil water content is at field capacity (mm); and p the fraction of Smax that a crop can extract from the root zone without suffering water stress (dimensionless). Grid-based data on total available water capacity of the soil (TAWC) at a 5 by 5 arc minute resolution were taken from ISRIC-WISE (Batjes, 2006). An average value of TAWC of the five soil layers was used in the model.