Fig. 1. WUE vs. VPD showing fit of Eq. [4], for crops with high (H, irrigated) or low (L, rainfed) water availability, during the period with green area index 5 in H crops. (a) VPD computed with = 0.50; line a: _H fitted with ß_H = –1; line b: _H and ß_H both fitted. (b) VPD computed with = 0.72 (adjusted for H crops); line a: _H fitted with ß_H = –1; line b: _L fitted with ß_L = –1, data from Exp. PE98 was excluded (see text). See Materials and Methods for explanation of the parameter, and Table 5 and Table 6 for fitting details.