Real-time flash flood forecasting approach for development of early warning systems: integrated hydrological and meteorological application

Abstract

This study proposes an integrated hydrometeorological modelling framework approach and methodology for flash flood Early Warning Systems in the Chugoku region of Japan. Unprecedented rainfall-induced hydrometeorological disasters and flash floods are increasingly occurring worldwide. Comprehensive efforts are conducted to simultaneously combine multiple disciplines into integrated modelling framework approaches to reduce disaster resilience. This enables more accurate hindcasts, reanalyses, real-time forecasts or nowcasts for flash floods. This study integrates proposed hydrological calibration approach with meteorological input. Two real-time rainfall forecasts by the Weather Research and Forecasting model forced by the Atmospheric Reanalysis v5 (ERA5) and the Japanese 55-year Reanalysis (JRA55) were used as input data to the hydrological model ensemble parameterized previously. This approach was applied to seven major rivers to evaluate river discharges real-time forecasts accuracy during the Heavy Rainfall Event of July 2018. Long lead-times of up to 29 h with a satisfactory reproducible range of Nash-Sutcliffe Efficiency were obtained using both meteorological forecast for all rivers cumulatively. This indicates that the proposed integrated hydrometeorological approach enables accurate flash flood real-time forecasting for this event. Similarly, the joint hydrometeorological approach enables framework for development of real-time flash food forecasting application in Japan and presumably worldwide.

HIGHLIGHTS

• Development of integrated hydrometeorological river discharge forecasts in real time.

• This study integrates hydrological ensemble calibration and meteorological forecasts.

• Weather Research and Forecasting (WRF) outputs with ensemble hydrological parameters.

• Long lead-times of 29 h with satisfactory accurate reproducibility were obtained.

• Our integrated hydrometeorological approach enables accurate river discharge nowcasts.

Keywords:

• Hydrograph forecast
• extreme river discharge
• 2018 Western Japan floods
• integrated hydrometeorological model
• ERA5 and JRA55 forcing
• real-time forecasting

Acknowledgements

The authors express sincere condolences to all the people who suffered any kind of damage from the natural disaster in the Chugoku region of Japan caused by the Heavy Rainfall Event of July 2018. A part of this study was supported by the Collaborative Research fund by the Disaster Prevention Research Institute (DPRI) at Kyoto University (PIs: Lee and Mori). Joško Trošelj is grateful and appreciative to his current advisor Naota Hanasaki for inspiring guidance and to his former Kyoto University’s Doctoral advisor Kaoru Takara and co-advisors Yosuke Yamashiki and Takahiro Sayama for providing source code and teaching methodology for proper usage of the CDRM model combined with the SCE-UA optimization method. Wahidullah Hussainzada developed an automatized Python script which enables faster modelling runs and can greatly reduce computational time when applied with multiple meteorological forecast simultaneously. Han Soo Lee, Syed Zeeshan Haider and Mahdi Khaleghi provided useful suggestions in the conceiving stage of the study. Kedar Otta discussed key parts of the study before submission and provided useful suggestions. Soumitra Pathak proofread English language corrections in main parts of the study. The Writing Center of Hiroshima University provided numerous useful suggestions to improve the quality of the writing and presentation of the contents.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available on a reasonable request from the corresponding author JT.