Diagnosing Sources of Caribbean Early Season Rainfall and Its End of Century Projection: Changes in the Caribbean-Rain Belt Pattern.

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Theodore L Allen, International Research Institute for Climate and Society, Columbia University, Palisades, NY, United States
The climate of the Caribbean is projected to become hotter and drier by the end of the 21st century. Average annual rainfall in the Caribbean is predicted to decrease by 20% within the next 80 years. A drier wet season (May-Sept.) will account for the majority of the annual rainfall decrease compared to changes in dry season rainfall (Dec.-Apr.). But, what exactly does “climate” represent and how is this translated to future projections?
 Climate is nothing more than an average of weather events. Weather events that contribute to the Caribbean early season rainfall are diagnosed from 2 ingredients: low level tropical moisture transport and uplift dynamics from upper level troughs that dig deep into the Caribbean during the late spring. Heavy rainfall is observed where these two conditions occur simultaneously. Accumulated rainfall during this time contributes to a quasi-stationary “Caribbean rain-belt” pattern that accounts for the first peak of the annual bimodal Caribbean rainfall pattern.
 Rather than thinking of a general drier Caribbean at the end of this century, we should instead consider changes in circulation that will alter the wet season weather events between May and June, including the “Caribbean rain-belt”. Altering expected weather events over time ultimately causes a change in anticipated climate by the end of the 21st century. Farmers who depend on a predictable series of familiar late spring rains and the “Caribbean rain-belt” may need to adjust to a new normal that includes fewer rainfall events and an overall drier wet season.