The projected temporal evolution in the interannual variability of East Asian summer rainfall by CMIP3 coupled models

Abstract

The projected temporal evolution in the interannual variability of East Asian summer rainfall in the 21st century is investigated here, by analyzing the simulated results of 18 coupled models under the 20th century climate experiment and scenario A1B. The multi-model ensemble (MME) mean projects two prominent changes in the interannual variability of East Asian summer rainfall in the 21st century under scenario A1B. The first change occurs around the 2030s, with a small change before and a large increase afterward. The intensity of the interannual variability increases up to approximately 0.53 mm/d in the 2070s, representing an increase of approximately 30% relative to the early 21st century. The second change happens around the 2070s, with a decrease afterward. By the end of the 21st century, the increase is approximately 12% relative to the early 21st century. The interannual variability of two circulation factors, the western North Pacific subtropical high (WNPSH) and the East Asian upper-tropospheric jet (EAJ), are also projected to exhibit two prominent changes around the 2030s and 2070 under scenario A1B, with consistent increases and decreases afterward, respectively. The MME result also projects two prominent changes in the interannual variability of water vapor transported to East Asia at 850 hPa, which occurs separately around the 2040s and 2070s, with a persistent increase and decrease afterward. Meanwhile, the precipitable water interannual variability over East Asia and the western North Pacific is projected to exhibit two prominent enhancements around the 2030s and 2060s and an increase from 0.1 kg/m2 in the early 21st century to 0.5 kg/m2 at the end of the 21st century, implying a continuous intensification in the interannual variability of the potential precipitation. Otherwise, the intensities of the three factors’ (except EAJ) interannual variability are all projected to be stronger at the end of the 21st century than that in the early period. These studies indicate that the change of interannual variability of the East Asian summer rainfall is caused by the variability of both the dynamic and thermodynamic variables under scenario A1B. In the early and middle 21st century, both factors lead to an intensified interannual variability of rainfall, whereas the dynamic factors weaken the interannual variability, and the thermodynamic factor intensifies the interannual variability in the late period.