Leading source and constraint on the systematic spread of the changes in East Asian and western North Pacific summer monsoon

Abstract

With ongoing global warming, the changes in EA-WNPSM rainfall-feeding over two billion people in East Asia and the Indochina Peninsula-projected by the Coupled Model Intercomparison Project Phase 5 (CMIP5) models show remarkable and unidentified inter-model spread. Here, we reveal the leading inter-model spread of EA-WNPSM changes in 28 CMIP5 models is related to a 'dry north-wet south' dipole in East Asia and a wet Indochina and WNP. This spread pattern of EA-WNPSM changes is induced by the spread of sea surface temperature changes in the equatorial western Pacific, and can be further traced back to an apparent discrepancy among the state-of-the-art models in simulating the tropical Pacific rainfall. An air-sea coupling processes involved with summer background circulation contribute to this robust spread pattern of EA-WNPSM changes. We can constrain the EA-WNPSM rainfall changes based on the current-future relationship and observation that there should be more rainfall increase in North China and the Korean Peninsula and less increase in South China, the Indochina Peninsula and WNP, relative to previous multi-model ensemble projections.

Inter‐model Spread of the Changes in the East Asian Summer Monsoon System in CMIP5/6 Models

“…Inter‐model MV‐EOF analysis was performed to extract the leading spread of the changes in the EASM, as in Zhou et al. (2019b). Compared with conventional EOF analysis, the MV‐EOF approach can capture the spatial relationship between several related variables (Wang, 1992; Wang et al., 2008), which was an efficient method in our study owing to the close correlation between the lower‐ and upper‐tropospheric circulation systems in the EASM.…”

“…The first mode in the inter‐model MV‐EOF analysis was selected, and the other variables related to the EASM were regressed onto the normalized first principal component [PC1; as Figure 1b in Zhou et al. (2019b)].…”

“…Understanding the response of the monsoon system to global warming is important to the projection of future regional climate (Christensen et al., 2013), which has been widely studied based on the future scenario simulations of the Coupled Model Inter‐comparison Project (CMIP; e.g., Hu et al., 2003 Kitoh et al., 2013; Lee & Wang, 2014; Turner & Annamalai, 2012). However, considerable inter‐model spread lowers the confidence in future projections (Christensen et al., 2013), which prompts studies on the source of the spread (e.g., Chen & Zhou, 2015; Li et al., 2017; Zhou et al., 2018, 2019b) and the underlying physical processes for building better climate models (Xie et al., 2015).…”

“…The responses of these components to anthropogenic warming are widely studied individually (He & Zhou, 2015; Horinouchi et al., 2019; Hu et al., 2003; Liu et al., 2014; Lu & Fu, 2010; Ren et al., 2017; Zhou et al., 2018, 2019b). The multimodel ensemble (MME) change in 500‐hPa eddy geopotential height shows a uniform weakening of the WNPSH in the middle troposphere (He et al., 2015).…”

“…In this study, we also first extracted the leading spread of the changes in the EASM, which is almost the same as Zhou et al. (2019b). Several indices were applied to quantify the changes in the WNPSH and EAJ and investigate their relationship with the leading spread.…”