Changes in occurrences of meteorological extreme events. Case Study: Brazilian main cities

Extreme weather and climate events have received increased attention in the last few years, due to the often-large loss of human life and exponentially increasing costs associated with them. Short-duration episodes of extreme heat or cold waves are often responsible for major impacts on society. Conversely, the location, timing, and magnitude of local and regional changes remain unknown because of uncertainties on future changes in the frequency and intensity of meteorological systems that cause extreme weather and climate events. It is likely that anthropogenic forcing will eventually cause global increases in extreme precipitation, primarily because of probable increases in atmospheric water vapour content and destabilization of the atmosphere. Relatively little work has been accomplished relating changes in high frequency extreme temperature events such as heat waves, cold waves, and number of days exceeding temperature thresholds. In this research, we explicitly model the tail regions of air-surface temperature, using the recent developments of extreme value theory, estimating the tails by fitting a Generalised Pareto Distribution (GPD) to the observations lying beyond certain thresholds that mark the beginning of the tail regions. There are different approaches to characterise the spatial behaviour of climatological phenomenon, and a particular elegant formulation is derived from the theory of point process governing peaks-over-threshold. Analysis of (1) trends in the number of warm days in Brazil and changes in the aestival season (spring throughout summer) length are investigated; (2) significant trends to fewer extreme minimum cold days and also trends to fewer warm maximum temperatures as well are analysed. The aim of this study is to verify whether extreme values related to weather attributes from several regions of Brazil (regional scale) show structural change, which can reflect the intended global change during the last century. For this purpose, daily extremes of air-surface temperatures and precipitation as well as the clustering of extreme temperatures defined by the peaks-overthreshold (POT) methodology are strongly indicated. The analysis of meteorological extreme events indicates that there has been a sizable change in their frequency in Brazil (urban behaviour). This suggests that natural variability of the climate system could be the cause of the recent changes, although anthropogenic forcing due to increasing greenhouse gases concentration cannot be disregarded. Like the exponential distribution, the GPD is often used to model the tails of another distribution. However, while the normal distribution might be a good model near its mode, it might not be a good fit to real data in the tails and a more complex model might be needed to describe the full range of the data. The GPD allows a continuous range of possible shapes that includes both the exponential and Pareto distributions as special cases. The empirical distributions focused in this study lead to a negative shape parameter, whose tails are finite. The number of warm nights is increasing on spring, summer and autumn! The number of warm days is increasing on summer! Almost certainly the summer nights are contaminating the spring nights and the autumn nights (maybe due to the urban heat island effect)! The longterm trend detected for TMIN and TMAX in some Brazilian regions indicate that the magnitude of the air temperature for the winter, spring and autumn are increasing. Probably the summer is invading or contaminating spring and spring is invading or contaminating winter in Brazil.Pages: 1539-154