ICAS External Seminar

Presented by Hugo Lambert, Exeter University

Land-ocean shifts in tropical precipitation under climate change

Host: Richard Keane

Abstract: Future changes in tropical precipitation are predicted to be dominated by shifts in patterns of rainfall rather than increases or decreases related to "thermodynamic" variables or changes in the overall strength of atmospheric circulation. In this talk, a new compositing scheme and simple theory that links potential future changes in rainfall to changes in surface temperature and relative humidity is used to analyse how rainfall shifts occur.

I begin by introducing relevant older study of land-sea temperature and moisture contrast, radiative forcing and decompositions that have been used to interpret modelled changes in tropical precipitation. The new scheme is then introduced, motivated by the tropical weak temperature gradient hypothesis. The success of the scheme in reproducing zonal shifts in precipitation in CMIP5 4xCO2 simulations under climate change, particularly away from Amazonia, is then shown. It is found that models for which the scheme is successful show rather different behaviour than models for which the scheme is unsuccessful. Some weaknesses of the methodology are then explored using idealised climate change simulations. I finish by proposing simple relationships for future tropical precipitation change, including a re-interpretation of the "rich-get-richer" / "wet get wetter" paradigm.

CV: Hugo completed his PhD in Atmospheric Physics at the University of Oxford in the UK, graduating in 2005. He then spent two years at University of California, Berkeley, followed by two years at the UK Met Office. He moved to Exeter University in 2010.

The seminar will be followed by cake and coffee in the School foyer.