[A-CG29] Extratropical oceans and atmosphere

[ACG29-P01] East-Asian atmospheric rivers bring more frequent and intense extreme rainfall under global warming

*Youichi Kamae¹, Yukiko Imada², Hiroaki Kawase², Wei Mei³ (1.Faculty of Life and Environmental Sciences, University of Tsukuba, 2.Meteorological Research Institute, Japan Meteorological Agency, 3.University of North Carolina at Chapel Hill)

Keywords:atmospheric river, heavy rainfall, global warming

In July 2018 and July 2020, East Asia experienced extreme heavy rain events. The heavy rainfall were observed over wide area because of contributions from organized water vapor flow called atmospheric river (AR). ARs, filamentary-shaped moisture transport bands, often bring heavy rainfall when they make landfall over the Northern and Southern Hemisphere middle latitudes. Recently, ARs have received increasing attention due to large social damages accompanied by such AR-related hazardous events. Under global warming, AR frequency should be increased because atmospheric moisture content is increased. In addition to such thermodynamic effect, dynamic effect related to atmospheric circulation should also be evaluated through global climate model tests. For evaluation of local extreme rainfall, fine-resolution regional climate models should be used because AR-related extreme rainfall is strongly influenced by orographic effect.

In this study, we use a set of high-resolution global and regional climate simulations called d4PDF to evaluate AR-related extreme rainfall and its change under global warming. Using d4PDF AGCM and RCM simulations, we identified great importance of ARs in extreme rain events in the future climate simulatioms. In the warming simulations, ARs are accompanied with more water vapor and sometimes bring record-breaking extreme rainfall when they make landfall over China, the Korean Peninsula and Japan. ARs account for 77% and 46% of increased occurrence of extreme rainfall in March-to-May and June-to-August, respectively. In this study, we only focus on role of ARs over East Asia. However, such great importance of ARs in future climate may also be found over western North America and Europe.