Warming causes more extreme shifts of the Southern Hemisphere’s largest rain band

CSIRO (Australia): South Pacific countries will experience more extreme floods and droughts, in response to increasing greenhouse gas emissions, according to a paper out today in the journal Nature.

The changes will result from the South Pacific rain band responding to greenhouse warming. The South Pacific rain band is largest and most persistent of the Southern Hemisphere spanning the Pacific from south of the Equator, south-eastward to French Polynesia.

Occasionally, the rain band moves northwards towards the Equator by 1000 kilometres, inducing extreme climate events. The international study, led by CSIRO oceanographer Dr Wenju Cai, focuses on how the frequency of such movement may change in the future.  The study finds the frequency will almost double in the next 100 years, with a corresponding intensification of the rain band.

Dr Wenju and colleagues turned to the extensive archives of general circulation models submitted for the fourth and fifth IPCC Assessments and found that increases in greenhouse gases are projected to enhance equatorial Pacific warming.  In turn, and in spite of disagreement about the future of El Niño events, this warming leads to the increased frequency of extreme excursions of the rain band.

During moderate El Niño events with warming in the equatorial eastern Pacific, the rain band moves north-eastward by 300 kilometres.  Countries located within the bands' normal position such as Vanuatu, Samoa, and the southern Cook Islands experience forest fires and droughts as well as increased frequency of tropical cyclones, whereas countries to which the rain band moves experience extreme floods.... 

The South Pacific rain band is largest and most persistent of the Southern Hemisphere spanning the Pacific from south of the Equator, south-eastward to French Polynesia. From the CSIRO web site