Probabilites of wet season dry spells for Brasília, D.F.

Abstract

For the Brasilia area, the wet season centers on the 5- month period - from November to March. This corresponds to the time of traditional cropping. Climatic limitations to agricultural production during this period were studied through analyses of daily rainfall for 42 years. Records analyzed from the standpoint of the single longest dry spell in any wet season revealed only an 8% chance that in any year the longest dry spell will be limited to 8 days or less, a 50% chance that the longest dry spell will be 14 days or more, and a 15% chance that the longest wet-season dry spell will exceed 3 weeks. The frequency of occurrence of multiple dry spells was revealed by analysis of all dry spells in the 42 years of record. On the average, the Brasilia area may expect 3 dry spells per wet season of 8 days longer spells of 10 days or longer, 1 dry spell of 13 days o, longer, and in 1 year in 7, wet-season dry spells will exceed three weeks in length. Wet season occurrence of dry spells was found to be most prevalent during late December and January. The tendency for wet-season dry spells is hidden in the monthly precipitation means. When monthly means were divided into time periods of 10 days in length, marked differences were observed between adjacent lo-days periods.