Water availability in a region is directly related to intensity and frequency of rain occurrence. Major occurrences of days with low amounts of precipitation can produce many losses, especially for agriculture. Thus, the objective of this study was to determine the probability of occurrence of dry periods in Rio Largo, Alagoas, Brazil, and to relate it to climate scale phenomena such as El Niño - Southern Oscillation (El Niño and La Niña). The dry periods were evaluated for three different time intervals with sequence of dry days (> 5 days, > 7 days and > 10 days). The sequence of days was defined as dry based on different thresholds of precipitation (< 0, 1, 2, 3, 4 and 5 mm). The end of each dry period was determined by the occurrence of a rainy day. Analyses were performed using the Instat Climatic application. The 5 days interval was the most frequent in the dry and rainy seasons. In the rainy season (April-August), this dry period had higher frequency of occurrence of 5-85%. While the occurrence of dry periods of 7 days (0 to 45%) and 10 days (0 to 5%) was lower. It was noted the strong influence of ENSO events (El Niño Southern Oscillation) in the occurrence of dry periods. In El Niño years, the occurrences were enhanced (10-60%), and reduced in years of La Niña events (0-45%).
rainfall; dry days; ENSO
