From 32 CRR‐catchment cases (combinations from four conceptual rainfall‐runoff models (CRR) and eight catchments) calibrated with either two or three optimization methods, (1) the shuffle complex evolution method (SCE‐UA), (2) the multiple start Simplex (MSX), and (3) the local Simplex, it seems that all three methods produced parameter sets of comparable, local‐optimum quality. Even with comparable performance among the models, some parameter values derived by the three optimization methods for the same CRR‐catchment cases are surprisingly different from each other. In addition, parameter sets of SCE‐UA or MSX, which often produce marginally better results than the local Simplex at the calibration stage, could end up with worse results at the validation stage. Apparently, given the inherent limitations of calibration data, model inadequacies, and identifiability problems, it is impossible to achieve global convergence in the parameter search. However, other than those for dry catchments such as Ihimbu or Bird Creek, the parameter sets obtained are generally feasible. Both SCE‐UA and the local Simplex are viable optimization tools, while MSX is inefficient computationally. SCE‐UA can complete the parameter search in one run, while the local Simplex often requires multirun operations to get good results.

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Using meteorological data collected in the summer of 0885 and 0886\ three evapotranspiration "ET# models\ the PenmanÐMonteith "PM#\ the modi_ed Penman for non!saturated surface\ and the two!source models were applied to estimate hourly ET from di}erent land!use covers of the Paddle River Basin "area 154 km 1 #[ By assuming closed canopy conditions\ the PM model could estimate the ET of coniferous forest and agricultural land because the contribution of soil evaporation under these land covers is not signi_cant[ For mixed forest and pasturelands that are partially vegetated\ however\ the amount of soil evaporation is signi_cant and so PM underestimated the total ET[ The modi_ed Penman model mainly underestimated hourly ET during daytime when the atmosphere is unstable\ but overestimated ET during early morning and late afternoon "stable atmosphere#\ particularly for pastureland[ By re!establishing a relationship for the relative evaporation\ the ET simulated by the modi_ed Penman model improved[ Both PM and the modi_ed Penman are assessed with respect to the comprehensive\ two!source model|s simulated ET because the latter agrees favourably with the ET obtained from the basin water balance[ The water balance ET is reliable because it is based on the stream~ow\ surface temperature\ net radiation and soil moisture simulated by the semi!distributed hydrological model\ Semi!distributed Physically based Hydrologic ModelÐRemote Sensing\ DPHM!RS "host to the two! source model#\ all of which have been demonstrated to agree well with the observed data[