Abstract
Under the future global warming conditions, increasing frequency of heavy rainfall and intensification of typhoons are assumed. To consider non-structural flood countermeasure, estimation of the maximum flood is important. In this study, a combined technique of ensemble numerical weather simulation and pseudo global warming (PGW) method was applied to a heavy rainfall event in the Tsurumi-gawa river basin, and future variations of the rainfall were examined. Future projections by multiple global climate models were used to prepare PGW conditions. Then, runoff-analyses were made by a distributed hydrological model with results of the weather simulations. Total and the maximum hourly rainfall in the Tsurumi-gawa basin showed significant increase in future climate conditions. Results of the hydrological simulations showed that river discharges were smaller than the design flood discharge in reproductive simulations. On the other hand, simulated river discharges exceeded the design-flood in most of simulations with future rainfall. Probability density of the maximum discharge of ensemble simulation were quite different between present and fucure climate conditions. And the results showed that probability of flood exceeding the design-flood or more is higher in future, and most of future simulation results exceed the maximum discharge in present simulation.
