Assessing Future Climate Changes in the East Asian Summer and Winter Monsoon Using Regional Spectral Model

This study investigated potential future climate changes over East Asia with a focus on temperature variation and changes in precipitation as well as future changes in the East Asian monsoon system. The current and future climate projection scenarios are downscaled over East Asia using the regional spectral model (RSM). The representative concentration pathways (RCPs) 2.6 and 8.5 scenarios driven by the Hadley Center Global Environmental Model version 2 (HG2) are used to provide large-scale forcing for the RSM downscaling simulations. Simulations were conducted for the current climate from 1980 to 2005 and two types of future climate between 2020 and 2100. Near-future (2025-2050) and far-future (2075-2100) climate simulations are compared with the current (1980-2005) climatology to investigate climatic change over East Asia. The RSM well captures the precipitation and temperature distribution related to the East Asian summer and winter monsoon and mesoscale mountain range with added values, although the wet and cold biases are aggravated in the RSM downscaling. Additionally, short time-scale phenomena such as daily mean temperature and daily precipitation are more accurately reproduced by the RSM than by the HG2. From future climate projection, the increasing temperature trends of each RCP scenario are consistently reproduced in the RSM downscaling; in particular, the result from the RCP 8.5 experiment shows a significantly steeper trend with increasing temperature. Meanwhile, the East Asian monsoon is intensified in the future climate projection by the strengthening North Pacific subtropical high and Okhotsk high in summer and intensified Siberian high in winter. These changes lead to an increase in precipitation for summer and a decrease for winter.