The southeast asian monsoon: dynamically downscaled climate change projections and high resolution regional ocean modelling on the effects of the Tibetan Plateau

The Southeast Asian Monsoon (SEAM) is strongly affected by the complex topography and land–sea interface over Southeast Asia (SEA), which combine to make simulation of the SEAM technically challenging. To adequately assess the regional climate change signal, we have employed the Weather Research and Forecasting (WRF) Model to dynamically downscale a global climate change projection produced with the Community Earth System Model using different physics configurations in WRF, constituting a 5-member physics mini-ensemble. All ensemble members consistently project an increase in average SEAM rainfall and an increase in the frequency of extreme events. A regional ocean model based upon the Coastal and Regional Ocean Community model system was then incorporated into the dynamical downscaling pipeline and this has also contributed to significantly further improving the simulations of both sea surface temperature and SEAM rainfall. Since the Tibetan Plateau (TP) is widely considered to act as an elevated heat source which contributes to driving the Asian monsoon system, a coupled dynamically downscaled simulation with flattened plateau has also been performed so as to investigate the role of TP in the SEAM at a higher spatial resolution than has previously been investigated. Significant decrease of precipitation and winds over SEA, as well as a later monsoon onset by 1 month, are documented for the no TP experiment. Extreme precipitation is less affected than average precipitation. Such changes are more important for the northern part of the domain and are significantly amplified in the dynamically downscaled WRF simulations when compared with the global simulations that employ significantly coarser resolution.