Regional climate change over southern South America: evolution of mean climate and extreme events

SOLMAN SILVINA ALICIA

San Pablo, Brasil

Workshop; First Ibero-Amercican Workshop on Climate Dynamics, Climate Change and Regional Climate Modeling; 2007

Universidad de San Pablo

A series of regional scenarios of climate change including present-day climate and two future emission scenarios is discussed with emphasis on extreme events. First, the capability of the regional model to simulate present-day regional climate over southern South America is discussed in order to identify systematic model errors, determine the added value of using a regional model  and  to derive the regional climate change pattern in terms of the mean climatic conditions, seasonal cycles and extreme events. The egional climate simulations were performed with the MM5 (Fith-generation Pennsylvania State University-NCAR /Penn State- NCAR) regional model nested within time-slice global atmospheric model experiments conducted by the HadAM3H (Hadley Centre). model for different periods. The evaluation of the present-day simulation allows us to assess that model biases are related to both deficiencies in the regional model configuration and deficiencies in the boundary conditions. In particular, the location and intensity of the Chaco Low (topographically-induced systems) is not well simulated affecting the moisture advection over La Plata basin and, in consequence, rainfall is underestimated over the region. West of the Andes  the overestimation of rainfall is related mainly to biases in the boundary conditions, which tend to produce too strong westerlies, and, in consequence, enhanced synoptic scale variability over the Pacific storm-track .  Biases in mean and maximum temperatures are consistent with biases in precipitation:  negative (positive) biases are found over regions where rainfall is overestimated (underestimated).  The regional model improves the simulation of extreme events compared with the global model. Concerning the main regional patterns of climate change we remark the southward extension of the summer mean Atlantic and Pacific subtropical highs , stronger westerlies, mainly during JJA, a general increase in precipitation in northern and central Argentina especially in summer and fall, increasing precipitation mainly due to more intense extreme events rather than more rainy days , a general decrease in precipitation in winter and spring mainly due to less rainy days, a large increase in precipitation over the southern Andes during winter and increase in extreme events, a large decrease in precipitation over subtropical Andes during winter and decrease in the frequency of wet days.