Austral summer precipitation interannual variability and trends over Southeastern South America in CMIP5 models

DIAZ, LEANDRO; VERA, CAROLINA

INTERNATIONAL JOURNAL OF CLIMATOLOGY

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2017

0899-8418

The purpose of this study is to assess the ability of Coupled Model Intercomparison Project 5 (CMIP5) models inreproducing the variability and change of the austral summer precipitation observed in Southeastern South America (SESA)along the 20th century and beginning of the 21st. Models show a reduction in mean precipitation biases and inter-modeldispersion, and a significant improvement in the representation of the leading pattern of precipitation interannual variability(EOF1), in comparison with Coupled Model Intercomparison Project 3 (CMIP3) models. Changes of the EOF1 activity inthe present climate, as represented by both, climate model simulations and rainfall gridded datasets, evidence an increase ofthe frequency of EOF1 positive events (associated with positive precipitation anomalies in SESA and negative ones in theSouth Atlantic Convergence Zone) and a decrease of the frequency of EOF1 negative events. Nevertheless there are still largeuncertainties due to model differences and the internal variability of the climate system. In order to reduce the impact of modeluncertainties, an ensemble of the climate simulations that represent better the features associated with EOF1 activity was built,regardless to which model they correspond. The results obtained with this ensemble confirm that largest precipitation trendsin SESA are those represented by climate simulations associated with an increase (decrease) of EOF1 positives (negative)events. It was also found that positive precipitation trends in SESA resulted from climate simulations forced by anthropogenicsources are the largest and significantly different from those from simulations forced by natural sources only, which are notsignificantly different from zero.