A GEV fit to Annual Temperature Extremes in Argentina: a Study of the 1976-77 Climate Shift

RUSTICUCCI MATILDE; TENCER, BÁRBARA

Beijing , China

Congreso; 10th International Meeting on Statistical Climatology (10IMSC); 2007

American Meteorological Society

Temperature extreme events are one of the most studied extreme events since their occurrence has a huge impact on society. In this study we fit a GEV distribution to annual temperature extremes in Argentina by the method of maximum likelihood estimation with the aim of studying the influence of the 1976-77 climate shift on the frequency of occurrence of temperature extreme events. A Kolmogorov-Smirnov goodness-of-fit test is performed in order to study whether the GEV distribution fits the observed annual temperature extremes satisfactorily. The bootstrapping technique is used to determine the critical value of the K-S statistic. Based on daily data, four different annual extremes are defined: the highest maximum (minimum) temperature of the year, and the lowest maximum (minimum) temperature of the year. The spatial distribution of return values of annual temperature extremes in Argentina for the period 1956-2003 shows that while maximum temperature (Tx) is expected to be greater or equal to 32ºC at least once every 100 years throughout the country -reaching values even higher than 46ºC in the central regions-, minimum temperature (Tn) is expected to exceed 16ºC -reaching 30ºC in the central and northern regions-. Cold annual extremes show larger gradients across the country, with Tx being lower than 8ºC at least once every 100 years, and Tn lower than 0ºC every two years with values even less than -10ºC in the southeastern part of the country. However, the frequency of occurrence of climatic extremes has changed throughout the globe during the twentieth century. Changes in return values of annual temperature extremes due to the climatic shift of 1976-77 in six long-term data sets are analysed. The lowest Tx of the year is the variable in which the shift 1976-77 is less noticeable. In most of the stations there is a decrease in the probability of occurrence of the highest Tx if we based our study on the more recent epoch, while the frequency of occurrence of the highest Tn enlarges. The most noticeable change in return values due to the shift 76-77 is seen in Río Gallegos where the 10-yr return value for the highest Tn increases from 13.7ºC before 1976 to 18.6ºC after 1977.