Assessing Future Changes in the East Asian Summer Monsoon Using CMIP3 Models: Results from the Best Model Ensemble

Abstract

Future changes in the East Asian summer monsoon (EASM) have been estimated from the six bestperforming models in phase 3 of the Coupled Model Intercomparison Project (CMIP3) included in the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). The composite mean rainband over East Asia during the summer season exhibits the characteristic EASM front relatively well with slightly less precipitation over east-central China and the baiu front aligned more steeply in the latitudinal direction. An ensemble from the coupled models that poorly simulated the EASM is shown to degrade the overall results, giving rise to an underestimation of the projected increase rate in precipitation. In a quantitative estimate, the 22-member ensemble-mean precipitation for the period 2079-99 is anticipated to increase by only 5%-10%, which is half the increase in the corresponding mean precipitation from the good models (10%-20%). Moisture budget analysis demonstrates that the good-model ensemble mean is in a much closer correspondence with observations than the poor-or all-model ensemble mean, supporting the reliable selection of the best-performing models. An increase in the vertically integrated moisture flux convergence is attributed to the enhanced precipitation in the future climate. In particular, a significant increase in atmospheric water vapor because of a warmer SST over the western Pacific plays a more critical role in the enhanced precipitation than a change in monsoonal low-level circulation does. In contrast to the apparent meridional shift of the primary location of the future EASM front presented in previous studies, the current analysis shows a negligible amount of meridional movement.

Extreme Precipitation Indices over China in CMIP5 Models. Part I: Model Evaluation

“…Different models with different weights are useful for a more precise future projection of extreme precipitation changes Knutti 2010), which will be the focus of our next work. Furthermore, regional climate downscaling studies using the best models in extreme precipitation, as we selected here, can be helpful to reach more accurate results for regional climate change (Seo and Ok 2013). It is worth noting that higher resolutions are expected to effectively improve models' capabilities for simulating precipitation in eastern China, but this expectation is not extendable to the western areas.…”

“…A suite of models performing substantially better than others should be selected and combined together to improve the credibility of projection. (Schmittner et al 2005;Pierce et al 2009;Knutti 2010;Chen et al 2011;Seo and Ok 2013).…”

Multimodel ensemble projection of precipitation in eastern China under A1B emission scenario

“…The effects of intermodel variability cannot be ignored in the multimodel projection system, which lead to the inconsistency in RCMs projection of summer precipitation. The CMIP3 multimodel ensemble reveals an increased summer precipitation over most of China during the 21st century under SRES A1B [ Chen and Sun , ; Kusunoki and Arakawa , ; Seo and OK , ; Sun and Ding , ] and shows both agreement and disagreement with the projections of multi‐RCM mean (MRM) in our study (Figure a), for example, the wetter conditions over Northeast China and lower reaches of the Yangtze River Basin in both CMIP3 and MRM. However, the decreasing trend is evident in MRM over North China and South China, which is different with the changes in CMIP3 models.…”

Evaluation of summer precipitation over Far East Asia and South Korea simulated by multiple regional climate models

“…The moisture flux magnitude was calculated as the square root of the quadratic sum of moisture transport (Sepulchre et al, 2010). The expansion of the North Pacific Subtropical High (NPSH) in JJA brings large amounts of ocean moisture from the North Pacific over South Korea inducing a northward shift of the EASM rainband (Lu et al, 2008;Yun et al, 2008;Seo et al, 2013;Lee and Wang, 2014). Compared to the ERA-Interim reanalysis, all three MMEs of RCMs underestimated the expansion of the NPSH around the Korean Peninsula in summer (Figure 5f,g, and h).…”