Abstract: The modified Gash model is commonly used to simulate the canopy interception process. We explored its applicability in a Platycladus orientalis pure forest and a mixed forest of P. orientalis andCotinus coggygria located in Badaling Forest Park of Beijing. Data from May to October in 2013 were collected and used to fit the modified Gash model. The sensitivity of the model parameters was analyzed. The results showed that the measured values of throughfall, stem flow and canopy interception in the P. orientalis pure forest were 395.2, 22.3 and 129.5 mmrespectively, and those measured values of the mixed forest were 414.6, 12.2 and 120.1 mm respectively. Based on the modified Gash model, the simulated values of throughfall, stem flow and canopy interception in the pure forest were 415.80, 18.04 and 113.09 mm respectively, with the relative errors being 5.2%, 19.0%, and 12.7% compared with the measured values. The simulated values of the mixed forest were 454.26, 10.27 and 82.40 mm, with the relative errors of 9.6%, 15.6% and 31.4%. The following indices, saturated canopy waterholding capacity (S), average rainfall intensity (R), average saturated canopy evaporation rate (E), canopy density (c), saturated trunk storage capacity (S_t) and stem flow coefficient (P_t) were used in the sensitivity analysis. The results of sensitivity analyses showed that, in the pure forest, when the parameters varied between -50% to -20%, the simulated canopy interception was the most sensitive to the parameter S, followed by c, R,E, S_t and P_t. When the parameters varied between -20% to 50%, the parameter S also was the most sensitive factor for the simulated canopy interception, followed by E,R,c, S_t and P_t. In the mixed forest, when the parameters varied between -50% to +50%, the simulated canopy interception was the most sensitive to the parameter S, followed by E, R, c, S_t  and P_t. According to results of accuracy analysis, we suggest that the modified Gash Model was more suitable for the P. orientalis pure forest than for the mixed forest of P. orientalis and C. coggygria. The parameter S was a primary factor affecting the accuracy of the model output.

Key words: Weibei rainfed highland, soil moisture control, dual mulching, soil moisture variation.