Asymmetry of tropical precipitation change under global warming

Abstract

[1] A clear trend of tropical precipitation changes induced by global warming is found in hemispherical averages of most climate model simulations as well as from observation. It is observed that in response to global warming, an asymmetric pattern develops between tropical precipitation changes in the northern and southern hemispheres, and this asymmetry is locked with the seasonal cycle of tropical convection. In boreal summer (winter), the northern hemispherical average departure from tropical mean increases (decreases), while the departure of the southern hemispherical average decreases (increases). This implies an enhanced seasonal precipitation range between rainy and dry seasons and an increased precipitation difference b e t w e e n n o r t he r n a n d s o uth e r n h e m i s p he r e s .

A Region at Risk:

“…Hence, the Indian monsoon is projected to increase in intensity and variability under unabated climate change. The finding is in agreement with previous studies which suggest that under global warming the seasonal precipitation range between the wet and dry seasons is enhanced in the tropics (Chou, Tu, and Tan 2007;Menon et al 2013). …”

Climatic risks and impacts in South Asia: extremes of water scarcity and excess

“…The winter (DJF) precipitation ( Figure OR3, middle row) shows a relative decrease in Pakistan and the central and northern regions of India, whereas the rest of the regions show inter-model uncertainty in the direction of change under the RCP8.5 scenario. This is in agreement with previous studies based on the IPCC AR4 (CMIP3) models (e.g., Chou et al, 2007), which suggest that the wet season gets wetter and the dry season gets drier. Under RCP2.6 the direction of the percentage change in winter rainfall shows large inter-model uncertainty over almost all regions of India.…”

Recent change of the global monsoon precipitation (1979–2008)

“…On the other hand, the NH-SH contrast exerts an opposing effect on the SHSM, offsetting the positive contribution of other contributing processes (such as the EP cooling-WP warming trend discussed above), leading to a weak trend in SH monsoon. The stronger interannual variation during the austral summer might also weaken the signal of the longterm SHSM trend (Chou et al 2007). As such, the ''warm land-cold ocean'' and ''warm NH-cold SH'' mechanisms can explain why the NHMPI has a strong upward trend, while SHMPI has a weaker trend.…”

“…9). On the other hand, the increasing land-ocean and inter-hemispheric thermal gradients are likely a consequence of the anthropogenic forcing because the projected future temperature change shows a robust warm NH-cold SH and warm land-cold ocean warming pattern (Chou et al 2007). …”