A climatonomic study of the Lake Ontario drainage basin

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Abstract
An evapotranspiration climatonomy model (Lettau and Baradas, 1973) designed to compute monthly runoff, actual evapotranspiration, exchangeable moisture level, and stored moisture change, and incorporating seasonally varying parameter values was applied to the Lake Ontario drainage basin and to subbasins within it. The model was refined and improved by using a ‘direct search’ optimization technique (Rosenbrock, 1960) to obtain monthly values of the set of prescribed parameters. The parameters were calibrated using data for 1969–1971 inclusive and for long‐term means. They were then applied to relevant 1972 data as an independent test of the validity of the model. The results were consistent and reasonably reliable by comparison with others. The parameter values are physically justifiable and in accord with comparable parameter values reported in the literature. Computed monthly runoffs are within 1.4% of observed streamflow in the unregulated subbasins and within 6.0% in one that is regulated. For the Lake Ontario basin as a whole, computed monthly runoff is within 7.0% of measured outflow adjusted for lake level changes. The agreement is within 3.5% in the case of annual values. Computed monthly actual evapotranspiration is in excellent agreement with other studies. It is concluded that the model, with a calibrated set of seasonally varying parameter values, is a viable approach for the study of the moisture regimes of catchments.