Twenty-first century projections of extreme precipitations in the Plata Basin

Abstract

Distributions of monthly rainfall averaged spatially over three regions of the La Plata Basin (LPB) were projected for 2011–2040 and 2071–2100 using outputs of four regional climate models (RCMs) nested in three different general circulation models, run with the SRES A1B emission scenario. Tuning of simulations with observations was done at the control period 1981–1990. During the past 50 years, in part of LPB, there was a positive trend in annual precipitation. Two of the models indicate the maintenance of this trend over the northeast of Argentina and south of Brazil, while over the southernmost region of LPB, all models show increasing precipitation throughout the twenty-first century. Trends are less ambiguous for extreme precipitation, especially in the southernmost part of LPB, where huge and long-lasting floods take place over plains with small drainage. Months with extreme precipitation in LPB present a pronounced annual cycle with higher frequency from October to April. According to the RCM projections, this pattern would persist during the twenty-first century. Although, other factors cannot be discarded, the projected trends towards higher extreme monthly precipitation seem to be caused by an increase in the moisture convergence in the lower atmosphere over the east of LPB.