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    Atmospheric and hydrospheric sciences


    d4PDF: large-ensemble and high-resolution climate simulations for global warming risk assessment

    Masayoshi Ishii, Nobuhito Mori

    Global warming, d4PDF, ensemble climate simulation, atmospheric model, dynamical downscaling, detection and attribution, impact assessment, climate change adaptation, natural hazard, storm surge

    Time series of global mean surface air temperature anomalies of d4PDF for past (light blue), nonwaming (blue), +1.5 K (green), +2 K (orange), and +4 K (red) climate simulations and CMIP5 historical and RCP8.5 experiments with six climate models. Shading indicates two-sigma uncertainties. Time series are drawn relative to the averages for the period from 1975 to 2005.

    A large-ensemble climate simulation database, which is known as the database for policy decision-making for future climate changes (d4PDF), was designed for climate change risk assessments. Since the completion of the first set of climate simulations in 2015, the database has been growing continuously. It contains the results of ensemble simulations conducted over a total of thousands years respectively for past and future climates using high-resolution global (60 km horizontal mesh) and regional (20 km mesh) atmospheric models. Several sets of future climate simulations are available, in which global mean surface air temperatures are forced to be higher by 4 K, 2 K, and 1.5 K relative to preindustrial levels. Nonwarming past climate simulations are incorporated in d4PDF along with the past climate simulations. The total data volume is approximately 2 petabytes. The atmospheric models satisfactorily simulate the past climate in terms of climatology, natural variations, and extreme events such as heavy precipitation and tropical cyclones. In addition, data users can obtain statistically significant changes in mean states or weather and climate extremes of interest between the past and future climates via a simple arithmetic computation without any statistical assumptions. The database is helpful in understanding future changes in climate states and in attributing past climate events to global warming. Impact assessment studies for climate changes have concurrently been performed in various research areas such as natural hazard, hydrology, civil engineering, agriculture, health, and insurance. The database has now become essential for promoting climate and risk assessment studies and for devising climate adaptation policies. Moreover, it has helped in establishing an interdisciplinary research community on global warming across Japan.