A second rainfall minimum has been identified during the rainy season in several regions of tropical South America. It has received names such as dry spells, veranicos, veranillos or mid-summer drought, and it consists of series of continuos dry days during the peak of the rainy season, and sometimes can extend up to more than 20 successive days with no or very little rain. In terms of agriculture, this dry spell can seriously affect crops if no soil moisture is available, due to little rain before the spell and the extension of it.
Based on daily data of rainfall from 25 years from the Brazilian Amazonia, a rgionalization is made for the month when the mid-summer drought occurs more often during the October-May period, that captures the rainy season in the entire region. Central equatorial and eastern near the mouth of the Amazon exhibit the mid-summer drought in November, while in northwest Amazonia it is detected in October. Western Amazonia shows the drought between January and April, while the southern sections shows it in April, and the eastern part shows it between January and March. On interannual time scales. El Nino and La Nina years show variations in this pattern, especially in the mouth of the amazon and the southern basin. On the longer term, there is not significant evidence that suggest systematic changes on the location and intensity of the mid-summer drought.
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