Effects of Climate Change on the Return Periods of Water and Sediment Discharge

Global climate change will have a significant impact on sediment discharge. Increase in sediment discharge will affect downstream riverbed form and channel conveyance capacity, causing damage such as levee breaks, overflows, and bridge failures. Climate change predictions require a large ensemble calculation to account for uncertainties. As a result, the calculation results of sediment discharge using the climate change predictions are also big-data. However, there is no established method for evaluating the results of these large sediment discharge predictions. In this study, we attempt to analyze the changes in return period using the abundant calculation results of sediment discharge.

Our study site is the upper reaches of the Pekerebetsu River in Hokkaido, Japan. The largest rainfall in this basin was recorded during the heavy rainfall in Hokkaido in August 2016. The model parameters were adjusted using the peak water discharge and cumulative sediment discharge during that event. Then, the water and sediment discharge were calculated from the large ensemble rainfall data for climate change prediction called as d4PDF and used for statistical evaluation.

Our calculation results indicate that climate change increases rainfall, water discharge and sediment discharge for a 100-year return period by a factor of 1.7, 2.4 and 6.7, respectively. Thus, the return period for a peak sediment discharge of 4 m3/s is currently 400 years but will be 50 years in the future. We also found that climate change causes a greater increase in sediment discharge from slope failures than from riverbed erosion．

Our results will contribute to the understanding of future landform changes and the planning of disaster prevention against climate change.