Várzea

Natural History

     Climate

Temperature:
    The central area of the Amazon is hot and humid, with a mean annual temperature of 80ºF.  Seasonally, this doesn't change much.  The warmest months are in August through November, when average temperatures are 81.5ºF. Coldest months are January, February, March, and April, when average temperatures are 78.6ºF.  Daily fluctuations in temperature are much more extreme, and temperatures can vary 18ºF or more.  In May, minimum temperatures plummet below 68ºF, when a cold, southern polar air mass moves northward.  This cold period is called a friagen.

Humidity:
    Relative Humidity is high year-round.  It averages 75.6% in Septemper, and 86.7 in April.  Evaporation can be greater than precipitation in the dry months.

Precipitaion:
    Precipitation is periodic.  The rainy season is from December to April, and the dry season is from June to October.  A shorter rainy season also occurs, for a period of only days to a few weeks, between October and December.  This short season has ecological impact on herbaceous plant growth, and on the breeding behavior of some birds.
    Total rainfall averages 2100 mm a year.  Local rainfall distribution varies greatly. Some evidence indicates that vàrzea may experience 45% less rainfall than the surrounding terra firme, which would of course have a large impact on plant and animal life (Junk 31).

Winds:
    Prevailing winds in the Amazon come from the east.  To the north of the Equator, the winds are the northeastern trade winds, and south of the Equator, they are the southeastern trade winds.  Either of these winds can be predominant in the region, depending on the displacement of the intertropical convergence zone (ITCZ).  The ITCZ moves north or south, depending on the placement of the thermal Equator and the annual variation in the declination of the sun.  

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