Amazon River Basin Rainfall in Average Year

The Amazon carries a large volume of water contributing 20% of global river runoff to the oceans. And has the largest rainfall runoff flood. Despite the large rainfall amounts a high proportion of this is lost to the atmosphere via evapotranspiration of the dense vegetation occupying large areas of the river basin. The highest estimates of runoff are for the period December to April, with lower basin averages occurring from May to August. Interestingly there is a slightly less evaporation occurring during the period May to August. This highlights the connection between evaporation and runoff, because less run off corresponds to a lowering of water available for evaporation.

Relative to other large river basins in the world the Amazon receives high levels of rainfall annually. The southern most tip and western edge of the basin receives the least amount of rainfall, which is typical for this mountainous region. In general rainfall levels are less at higher altitudes compared to the lower reaches of the river basin. The tropical rainforest that occupies a large proportion of the basin is supported by high amounts of rainfall, where on average annual rain fall is over 3,000 millimetres. There are noticeable variations in the total amounts of rainfall between the years with the north western section receiving the maximum amounts of rainfall.

Average Total Rainfall (mm/yr)

Bargraph referencing the colours on the rainfall maps.

Other Amazon Maps

Amazon Rainfall Maps