Effect of time scale on flood simulation: maximum rainfall intensity and fractal theory based time disaggregation method for rainfall

The time scale of rainfall data limits the accuracy and application scope of hydrologic models, especially when low-accuracy observed rainfall data are used in physically based distributed hydrologic models. In this study, an optimized rainfall method based on maximum rainfall intensity and self-similarity was established to provide different rainfall data for the physically based distributed hydrological model. The results showed the following: (1) the increase of time scale resulted in decreased rainfall intensity and an evenly distributed rainfall pattern; (2) the established disaggregation method for rainfall well described the uneven distribution in time; (3) the influence of time scale could be divided into 1-20, 20-120, and 120-360 min; (4) the conversion method between rainfall intensity and saturated hydraulic conductivity was effective at ensuring the physical meaning of the parameters on a time scale of 20-90 min. Furthermore, results showed that the reasonable time scale of application of the CASC2D model is less than 120 min. For longer time scales, the model was able to simulate peak discharge but unable to describe the flood process.