Behind uncertainties in projections of Australian tropical climate: Analysis of 19 CMIP3 models

Abstract

[1] A systematic study is undertaken for projected changes in tropical Australian climate in 19 CMIP3 Coupled Models for the A2 scenario over the 21st century. While equatorial regions to the north of Australia are projected to have increased precipitation during austral summer (December to February) by the end of the 21st century, there is no significant change over northern Australia based on the model ensemble mean. There is a large spread in model simulations of precipitation change, with both large positive and negative anomalies. The ensemble mean change in the seasonal cycle of precipitation over tropical Australia is small, with precipitation increase during March and April, suggesting a prolonged Australian wet season. There is no model consensus on how interannual variability of tropical Australian precipitation will change in future climate, although more models simulate increased variability than decreased. Correlations between full wet season (October to April) precipitation and austral spring (September to November) NINO3.4 sea surface temperature anomalies show a slight weakening. The spread in projected precipitation seasonal cycle changes between simulations from the same model is larger than the inter-model range, indicating that there is large internal or natural variability in tropical Australian precipitation relative to the climate change signal. Zonal wind changes indicate an intensification of austral summer low level westerlies although combined with a weakening of upper easterlies. Low level westerlies also persist for longer, consistent with a delay in the monsoon retreat. All models simulate an increase in the land-ocean temperature contrast in austral summer, with a significant correlation between changes in land-ocean temperature contrast in the pre-monsoon (austral spring) and summer precipitation changes. Analysis of precipitation changes using regime-sorting techniques shows offsetting tendencies from thermodynamic changes associated with enhanced atmospheric moisture and dynamic changes associated with a weakened atmospheric circulation.

Future change of the global monsoon revealed from 19 CMIP5 models

“…Further analysis indicates that the thermodynamic effect contributes positively to the moisture convergence, but is partly offset by the dynamic effect associated with a weakened monsoon circulation. The offsetting effect between the thermodynamic and dynamic components of the moisture convergence process was also seen in the modulation of regional monsoon rainfall changes [Cherchi et al, 2010;Moise et al, 2012]. Fewer studies have discussed the moisture processes related to surface evaporation change over monsoon regions.…”

“…Over the South/East Asian monsoon regions, the intensification of summer monsoon rainfall and its interannual variability have been widely detected within model projections [Hu et al, 2000;May, 2002;Meehl and Arblaster, 2003;Kitoh et al, 2005;Ueda et al, 2006;Annamalai et al, 2007;Lu and Fu, 2010;Turner and Annamalai, 2012]. Based on the Coupled Model Intercomparison Project Phase 3 (CMIP3) multimodel data set, Moise et al [2012] found that the overall Australian summer monsoon precipitation showed little change, but the length of the wet season had increased slightly by the end of 21st century. Considering future changes in the African monsoon system, Shongwe et al [2009] showed that the rainy season over Southern Africa tends to become shorter in a future climate (2051-2200) under the CMIP3 A1B scenario, whereas Cook and Vizy [2006] suggested that no consensus has been achieved over the West African monsoon regions.…”

A global evaluation of fronts and precipitation in the ACCESS model

“…in climate models (Williams and Tselioudis 2007;Brown et al 2010;Stephens et al 2010) and to look at trends and future changes in clouds and precipitation (Bony et al 2004, Williams and Tselioudis 2007, Catto et al .2012b, Moise et al 2012. We can think of the presence of fronts as a type of regime, with the other regime being the no-front case.…”

Evaluation of CMIP3 and CMIP5 models over the Australian region to inform confidence in projections

“…The Australian monsoon is the main driver of annual variation in the tropical regions (Trenberth et al 2000;Wang and Ding 2008;Moise et al 2012) and therefore is an important feature for climate models to correctly simulate. This will also enhance confidence in future projections of mean changes and associated impacts (Colman et al 2011).…”