Tropical drying trends in global warming models and observations

Abstract

Anthropogenic changes in tropical rainfall are evaluated in a multimodel ensemble of global warming simulations. Major discrepancies on the spatial distribution of these precipitation changes remain in the latest-generation models analyzed here. Despite this uncertainty, we find a number of measures, both global and local, on which reasonable agreement is obtained, notably for the regions of drying trend (negative precipitation anomalies). Models agree on the overall amplitude of the precipitation decreases that occur at the margins of the convective zones, with percent error bars of magnitude similar to those for the tropical warming. Similar agreement is found on a precipitation climate sensitivity defined here and on differential moisture increase inside and outside convection zones, a step in a hypothesized causal path leading to precipitation changes. A measure of local intermodel agreement on significant trends indicates consistent predictions for particular regions. Observed rainfall trends in several data sets show a significant summer drying trend in a main region of intermodel agreement: the Caribbean͞Central-American region.climate change ͉ tropical precipitation ͉ drought

Exacerbation of the 2013–2016 Pan‐Caribbean Drought by Anthropogenic Warming

“…Notably, climate models consistently simulate significant decreases in precipitation in the Caribbean as anthropogenic greenhouse‐gas concentrations increase in the future (IPCC, 2014; Neelin et al, 2006), and if those trends are already underway, then the total contribution of anthropogenic climate change would be greater than that estimated here.…”

“…Since 1950, the Caribbean has seen a gradual drying trend (e.g., −0.09 self‐calibrating Palmer Drought Severity Index [scPDSI] units per decade; Dai, 2011; Herrera & Ault, 2017; Neelin et al, 2006; Sheffield et al, 2012) with several multiyear droughts, the most severe and widespread of which occurred between 2013 and 2016 (Herrera & Ault, 2017). Given its extensive spatial scale, we refer to this event as the Pan‐Caribbean Drought (Figure 1).…”

A review of observed and projected changes in climate for the islands in the Caribbean

“…This drying is thought to be related to several interdependent factors such as expansion and intensification of the NASH (Rauscher et al, 2008), an increase in wind speeds over the Caribbean Sea (Cook and Vizy, 2010;Taylor et al, 2011Taylor et al, , 2012, SST warming in the tropical North Atlantic (Rauscher et al, 2011), and a decrease in precipitation in regions along the margins of convective areas in the tropics (Chou and Neelin, 2004;Neelin et al, 2006). The RCM used in this study gives very different results when driven by boundary conditions from two different GCMs.…”

“…It is most closely related to SSTs in the South Caribbean Sea, and somewhat to the tropical North Atlantic SSTs (Spence et al, 2004;Stephenson et al, 2007). Neelin et al (2006) show that the Caribbean is drier by 1-12 mm per month or 5-30% of rainfall per 100 years with a trend that is significant at 5% level. Singh (1997) shows a decrease in precipitation for five of the eight stations across the Caribbean, with the exceptions being the Bahamas, Venezuela and one of Trinidad's stations.…”

“…The number of consecutive dry days has decreased and the trend is significant at the 1% level . Additionally, Neelin et al (2006), using station and satellite precipitation data, show a drying trend between June and August in the Caribbean in the last few decades.…”