Projections of tropical cyclones affecting Vietnam under climate change: downscaled HadGEM2-ES using PRECIS 2.1

Abstract

The potential changes in tropical cyclone (TC) activity, and the associated large-scale environmental conditions, for Vietnam and the South China Sea, posed by climate change, are examined using a high-resolution regional climate model system, PRECIS 2.1, to downscale the Met Office Hadley Centre CMIP5 model, HadGEM2-ES, to a resolution of 25 km (PRECIS_Had2). The ERA-Interim reanalysis is also downscaled to the same resolution (PRECIS_ERAI) for comparison. An objective algorithm is used to identify and track the TCs. The PRECIS_Had2 is evaluated for the period of 1990–2005 by comparing with the PRECIS_ERAI and the observed best-track data of TCs. Compared to PRECIS_ERAI, PRECIS_Had2 represents the TC-associated large-scale environments reasonably well but shows stronger vertical wind shear over the South China Sea and during the summer southwesterly monsoon. For TCs, PRECIS_Had2 is capable of capturing the TC distribution but shows a notable underestimation of very intense TCs. The analysis of the influence of global warming on the TC activity reveals that PRECIS_Had2 simulates a pronounced seasonal shift of TC activity in a warmer climate for both the RCP4.5 and RCP8.5 scenarios, with an increase in TC activity during winter related to the more favourable large-scale conditions, while a decrease in TCs associated with less favourable large-scale conditions is projected in summer.