Freqüência de chuva e ocorrência de seca na microrregião de Paragominas PA.

The objective of the present work was to determine rainfall frequency and occurrence of drought for the microregion of Paragominas, Pará, Brazil. For this, monthly frequency analysis of the rainfall was performed at levels of 20%, 50% and 80% using resources from the Rain Program, developed by Embrapa. Determination of drought occurrence was done by analyzing annual rain sensitivity around the average and the standard deviation, following orientation of the World Meteorological Organization. The general characterization of the climate was also performed by using agrometeorological models including water balance and climatic classification. The results showed that the pattern of the local rains presents great monthly and annual fluctuation. For the 80% frequency, the monthly of rain had been superior to the reference evapotranspiration only between December and March. The evidence of occurrence of seasonal drought was also observed. These situations indicate that in relation to short cycle crops dependent only on the rain water offers, the period between December and February, the most of the time, is the most appropriate for sowing in order to reduce climactic risks for these crop