Consistent increase of East Asian Summer Monsoon rainfall and its variability under climate change over China in 34 coupled climate models

Abstract. The East Asia Monsoon (EAM) dominates the climate over the densely populated East China and adjacent regions and is therefore influencing a fifth of the world's population. Thus, it is highly relevant to assess the changes of the central characteristics of the East Asian Summer Monsoon (EASM) under future warming in the latest generation of coupled climate models of the Coupled Model Intercomparison Project Phase 6 (CMIP6). Using 34 CMIP6 models we show that all models that capture the EASM in the reference period 1995–2014 within two standard deviations project an increase in June–August rainfall independent of the underlying emission scenario. The multi-model mean increase is 17.2 % under SSP5-8.5, 12.7 % under SSP3-7.0, 11.9 % under SSP2-4.5 and 11.2 % under SSP1-2.6 in the period 2081–2100 compared to 1995–2014. For China, the projected monsoon increase is slightly higher (12.1 % under SSP1-2.6 and 19.1 % under SSP5-8.5). The EASM rainfall will particularly intensify in South-East China, Taiwan as well as North Korea. The multi-model mean indicates a linear relationship of the EASM rainfall depending on the global mean temperature relatively independent of the underlying scenario: Per degree of global warming, the rainfall is projected to increase by 0.14 mm/day which refers to 3 % of rainfall in the reference period. It is thus predominately showing a "wet-region-get-wetter" pattern. The interannual variability is also robustly projected to increase between 7.0 % under SSP1-2.6 and 31.4 % under SSP5-8.5 in the multi-model mean between 2050–2100 and 1965–2015. Comparing the same periods, extremely wet seasons are projected to occur 6.5-times more often under SSP5-8.5.