The region of Belém, capital of the state of Pará, is a location vulnerable to the impact of storms during the year. The heavy rains bring problems to the population, as the flooding of streets and houses, disruption in the power supply and telecommunications, health problems, transportation, and in some cases, even death. This research sought to answer the following questions: What are the mechanisms that cause extreme events of precipitation in the rainy season and dry season? Are the thermodynamic instability indexes appropriated for predicting storms and heavy rain in the region? Is the effect of "Heat Island" affecting the convection in the city, causing an increase in the number and intensity of storms? What is the behavior of extreme events in years of El Niño and La Niña? What are the main social-economic impacts from the storms? Studying basically a time series of daily rainfall, data from soundings and reports published in local newspapers about the damage caused by storms, is that we tried to answer such questions. The results show that, in general, the Convective Available Potential Energy (CAPE) for extreme events in the dry season is greater than in rainy season, because the precipitation in the dry season is very much dependent on the thermodynamic forcing, then, to occur, there must be forcing of a mesoscale (instability line) and the CAPE and the indexes of instability must be very high. In the rainy season extreme precipitation is caused by the interaction between scales, the forcing dynamics (intertropical convergence zone) and thermodynamic forcing, in some cases into the interaction of the mesoscale forcings. The results are huge losses to the population. The data analysis of soundings shows that the indexes of instability are suitable for the rainy season and should be changed to the dry season, but may provide a subsidy for development of regional models, and when analyzed together with CAPE, satellite images and observations of wind field, makes possible the forecast of severe storms, helping decision-makers bodies.
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