The rainy season in the Amazon generally runs from December through May, when monthly rainfall can exceed 8 inches (20 centimeters). But the Amazon basin spans multiple countries and climatic zones, so the exact timing shifts depending on where you are. The driest month across the basin is August, when rainfall drops to around 2 inches (5 centimeters).
Rainy Season Timing by Region
The Amazon basin covers roughly 2.7 million square miles across nine countries, so there is no single rainy season. The southern, northern, and western portions each follow different schedules.
In the Peruvian Amazon (the western basin), heavier rains arrive from November through April. This is the classic wet season most travelers hear about, with warm temperatures and frequent afternoon downpours that can last for hours.
The Bolivian Amazon (southern basin) follows a similar pattern: heavy rainfall from November to March, with lighter rains from April through September. This southern schedule lines up closely with the South American summer.
The Ecuadorian Amazon (closer to the equator) flips the calendar. Rain becomes more frequent starting in March and continues through July. January through March is actually the least rainy stretch, making it the closest thing to a dry season in that part of the forest. If you’re planning a trip to Ecuador’s Amazon region expecting dry weather in April, you’ll be caught off guard.
The Brazilian Amazon, which makes up the largest share of the basin, broadly follows the December-to-May wet pattern measured by NASA, but local variation is significant depending on proximity to the equator and major river systems.
What the Wet Season Looks Like on the Ground
During peak months, the Amazon doesn’t rain nonstop. Mornings are often clear or partly cloudy, with intense rain arriving in the afternoon or evening. Humidity stays high year-round in the Amazon, but during the wet season it rarely drops below 80 percent. Temperatures hover between 77°F and 90°F (25°C to 32°C) throughout the year, with little difference between seasons. The real change is in the water, not the thermometer.
River levels rise dramatically during the wet months. In parts of the western Amazon, the difference between high and low water can reach 30 feet or more. Vast stretches of forest floor disappear underwater, creating what locals call the flooded forest. Two types of flooded forest dominate the basin: nutrient-rich floodplains along white-water rivers, and nutrient-poor zones along black-water rivers. Both flood annually, but the white-water floodplains receive fresh sediment deposits each cycle, making them more productive ecosystems.
How Flooding Shapes Wildlife
The wet season reshapes animal behavior across the basin. Fish populations surge during high-water years as flooded forests open up new feeding and breeding habitat. Waterfowl and giant otters also thrive when water levels are high, taking advantage of the expanded aquatic environment.
Ground-dwelling mammals tell a different story. Research in the western Amazon found that during consecutive years of intense flooding, populations of terrestrial mammals like large rodents and ungulates dropped by as much as 95 percent. These animals simply lose their habitat when the forest floor is submerged. Arboreal species, including primates, macaws, and wild cats, remain largely unaffected because they live in the canopy above the floodwaters.
For birdwatchers, the wet season is a mixed bag. Macaw populations stay stable regardless of flood intensity, and game birds like guans and curassows maintain consistent numbers. But species composition can shift: during years of heavy flooding in the western basin, some macaw species increase while others decline, suggesting they compete for resources differently when conditions change.
Traveling During the Rainy Season
High water actually opens up parts of the Amazon that are inaccessible during the dry season. Rising rivers turn narrow creeks into navigable channels, letting boats reach hidden lagoons and remote stretches of flooded forest. On river cruises, the wet season means skiff expeditions through submerged canopies where you’re paddling at eye level with branches that would normally be 20 feet above your head. It’s a surreal landscape and one of the best settings for photography.
The trade-off is that jungle trekking becomes limited. Trails flood, mud is constant, and some land-based excursions simply aren’t possible. If hiking through the forest floor is your priority, the dry season (roughly June through October in most of the basin) is better suited. During low water, exposed riverbanks and dry forest trails make overland exploration easier, and receding waters concentrate wildlife around shrinking pools and rivers, sometimes improving visibility for certain species.
The Rainy Season Is Getting Less Predictable
The Amazon’s seasonal rhythms are shifting. Satellite observations and rain gauge data from 1981 to 2019 show that large portions of the basin have experienced reduced dry-season rainfall, while wet-season flooding has intensified. In the western Amazon, greater-than-normal floods occurred in 2009 and in every year from 2011 to 2015.
Climate modeling suggests the trend will continue. Deforestation and global warming are individually lengthening the dry season and reducing total annual rainfall across South America. When both factors are combined in projections, the Amazon basin faces a potential 44 percent reduction in mean annual rainfall and a 69 percent increase in dry season length. The mechanism is straightforward: as forest is converted to open land, the trees that pull moisture inland from the Atlantic and release it back into the atmosphere disappear, and the conveyor belt of rainfall weakens.
For travelers, this means the traditional calendar of wet and dry months is becoming less reliable. Seasons that once arrived on schedule may start later, end earlier, or deliver unexpected extremes. Checking recent conditions for your specific destination, rather than relying on historical averages alone, is increasingly important when planning a trip.