Simulations of trends of extreme events in temperature and precipitation in South America using the IPCC AR4 models

JOSE A. MARENGO, MATILDE RUSTICUCCI, M. LABORBE, OLGA PENALBA, MADELEINE RENOM

Conferencia; An Earth System Science Partnership Global Environmental Change Open Science Conference; 2006

One of the most important questions regarding short-term extreme events is whether their occurrence is increasing or decreasing over time; that is, whether the envelope within which these events preferentially occur is experiencing a trend on present climate. Variability and changes in the intensity and frequency of extreme events depend not only on the rate of change of the mean of a selected variable but also on whether there are changes in the statistical parameters that determine the distribution of that variable.    The    most    difficult    trend analysis is that of extreme precipitation because of the small radius of correlation of many precipitation events. Therefore, reliable estimates of trends in extreme precipitation events are possible only for regions with dense networks that have remained stable over time. A lack of long-term observations over large parts of South America is the biggest obstacle in quantifying the change in extremes during the pastOn this paper we examine temperature and rainfall extreme indices available from eight IPCC AR4 coupled climate models for the XX Century (referred as IPCC AR4 20C3M). Even though the simulations are available since 1900 (some of them go back to 1860), trends of the modeled extreme indices are compared to observations during 1960-2000, mostly because the availability of observed indices of extremes. This period was selected because of the availability of homogeneous and quality controlled observed temperature and precipitation data was available for that period. The comparisons between observed and simulated indices are made to determine reasonableness of the simulated indices for present climates. Finally, we discuss the uncertainties in the predicted extremes changes rainfall changes and their potential impacts on the regional climates and their consequences in society.