VALIDATION OF A MODEL OF ACTUAL EVAPOTRANSPIRATION FOR WATER-STRESSEDSOYBEANS

In this paper a model for estimating actual evapotranspiration (ET) is tested at two experimental sites in Europe (southern Italy and southe rn France), using data for soybean crops temporarily stressed, grown u nder a typical Mediterranean climate. The present ET model is based on the Penman-Monteith approach, but uses a canopy r(v) value that takes account of both stomatal resistance and canopy architecture. In this model, r(v) appears only as r(v)/r(a), where r(a) is aerodynamic resis tance. r(v)/r(a) is set to a fraction of the ratio r/r(a) (with r* ca lled the critical resistance, similar to the isothermal resistance). T he function r(v)/r(a) = f(r/r(a)) depends on crop water status as spe cified by the predawn leaf water potential. The model gives very good results for both sites on hourly, daily and seasonal time scales. (C) 1997 Elsevier Science B.V.