An integrated time-varying moment (ITVM) model for flood frequency re-analysis under future climate change conditions

Abstract

The frequency analysis method is commonly used to calculate design floods. Under the double challenge of the non-stationary situation under the changing environment and the inadequate length of flood series, developing a new method to integrate the historical extraordinary floods into the non-stationary frequency analysis is essential. First, the Multi-Model Ensemble projections of temperature and precipitation based on Global Climate Model outputs were employed to drive the Soil & Water Assessment Tool hydrological model for runoff simulation. Then, the Integrated Time-Varying Moment (ITVM) model was developed to re-analyze the design floods based on the Pearson-III distribution. The calibrated SWAT model can satisfactorily simulate the rainfall-runoff relationship in the Yalong River basin. The developed ITVM model is effective to conduct the design flood frequency analysis to cope with the problems of insufficient length and non-stationarity of the flood series. The design flood values of Maidilong station show an obvious increase, with variations of 6.5%–9.4%, 2.9%–12.3%, and 16%–33.7% for SSP1-2.6, SSP2-4.5, and SSP5-8.5, respectively. The significant increase of low frequencies (p = 0.2%, p = 0.1%) floods, especially for SSP5-8.5 scenario, requires more attention, as the increased floods may exceed the discharge capacity of the reservoir determined at the design stage.