Preprints
https://doi.org/10.22541/essoar.170365204.46854879/v1
https://doi.org/10.22541/essoar.170365204.46854879/v1
13 May 2024
 | 13 May 2024
Status: this preprint is open for discussion.

Reduction of the uncertainty of flood hazard analyses under a future climate by integrating multiple SSP-RCP scenarios

Yuki Kimura, Yukiko Hirabayashi, and Dai Yamazaki

Abstract. The uncertainty due to small number of ensemble members is a major source of uncertainty in future climate predictions. While the uncertainty due to the above in general circulation models (GCMs) projections can be mitigated by increasing the number of simulation ensembles, only a limited number of large-ensemble experiments are available in CMIP6 future scenario experiments. Here we propose a method that increases the sample ensemble size in evaluations of future hazard, by integrating multiple SSP-RCPs for a time period corresponding to a specific increase in temperature from the preindustrial level (i.e., X °C warming). The success of the method was assessed by investigating whether the uncertainty due to small number of ensemble members could be reasonably reduced. First, the similarity in the spatial distributions of flood hazard projection at the same warming level was determined for different SSP-RCP scenarios. Under a 2 °C warming, all SSP-RCPs had a similar distribution with respect to the change ratio of the flood magnitude. Additionally, we showed that the uncertainty due to the different SSP-RCPs (5 %–10 %) was smaller than the differences between different warming levels such as between 2 °C and 3 °C (around 20 %–30 %), which suggests that differences among SSP-RCPs as to future flood discharge change are relatively small. These results suggested that integrating SSP-RCPs to increase the ensemble size was a reasonable approach, reducing unbiased variance among GCMs in about 70 % of land grid points comparing to the result using SSP5-RCP8.5 alone.

Yuki Kimura, Yukiko Hirabayashi, and Dai Yamazaki

Status: open (until 24 Jun 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Yuki Kimura, Yukiko Hirabayashi, and Dai Yamazaki
Yuki Kimura, Yukiko Hirabayashi, and Dai Yamazaki

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Short summary
The limited number of ensemble members causes uncertainty in future climate predictions. To address this, using multiple simulations under a single future climate scenario can increase the sample size, but data availability is limited in the scenario-based future projection experiment of climate model intercomparison projects. Our proposed method integrates multiple climate scenarios at specific temperature increases, effectively reducing uncertainty in future flood hazard assessments globally.