Rainfall -runoff modelling

Rainfall-runoff transformation is a complex process, To develop effective rainfall-runoff models it may be necessary to start with simple models, modify them and compare their performances with accuracy criterion. Seasonal Model, Linear Model and Linear Perturbation Model were applied to six catchments: Bird Greek (U.S.A). Kizu(Japan),Wollombi(Australia). Chaiping (Hanjiang). Pampanga(Phillipines) and Bai He (China). The pulse response function for Linear and Perturbation models were estimated by ordinary least squares. Nash and Sutcliffe efficiency criterion (R2 was used to compare model performances). The models were found to be inefficient with the following calibration and verification efficiencies: Seasonal Model (3,81% to 14.12%, -28.75 to 6.10%); Linear Model (47.18% to 79.18%. -53,21% to 70.61%); Perturbation Model (50,69% to 82.91%, -44.76% to 73.21%) respectively. The poor results show that the catchments do not show marked seasonal character. Soil Moisture Deficit Distribution and Routing (SMDDR) Model was developed. It had a water balance component which accounted substantially for catchment nonlinearities caused by evapatranspiration. There was marked improvement in the results. Calibration and verification efficiency ranges were 70.09% to 86.85%. and 40.O6 to 88.92% respectively. The routing component was the Linear model. Kizu, Pampanga, and Bai He could be represented by SMDDR model. SMDDR model structure needs modifications for Bird Greek, Wollombi and Chaiping. SMDDR is suitable for catchments where evapotranspiration controls generated runoff. The model was insensitve to the shape of pulse response function. If properly applied, the proposed Soil Moisture Deficit Distribution and Routing (SMDDR) Model may may be applied to a variety of catchments with success.