The savanna climate is defined by two distinct seasons: a warm, rainy wet season lasting six to eight months and a hot, dry season lasting four to six months. Average annual rainfall falls between 50 and 150 centimeters (20 to 59 inches), and temperatures stay warm year-round, never dipping below 18°C (64°F) in any month. This sharp seasonal swing between soaking rains and prolonged drought shapes everything about life on the savanna, from the grasslands and scattered trees to the massive animal migrations.
Two Seasons, Not Four
Unlike temperate regions with four seasons, savannas operate on a two-season cycle driven by a massive belt of warm, rising air near the equator called the Intertropical Convergence Zone (ITCZ). This belt follows the sun’s position throughout the year, shifting north during the Northern Hemisphere’s summer and south during its winter. When the ITCZ sits over a savanna region, moisture-laden winds sweep inland and deliver heavy rainfall. When it moves away, dry winds take over and rain essentially stops.
The result is predictable and extreme. In the Northern Hemisphere, the wet season typically runs from May to July and into the fall, while Southern Hemisphere savannas get their rain from November through February. Closer to the equator, some savannas experience two shorter wet seasons per year as the ITCZ passes overhead twice. Farther from the equator, those two rainy periods merge into a single prolonged monsoon-like wet season with a longer corresponding dry spell.
Temperature Ranges Across the Year
Savannas are consistently warm, but the two seasons feel noticeably different. During the dry season, average monthly temperatures range from about 10 to 20°C (50 to 68°F). In the wet season, that range climbs to 20 to 30°C (68 to 86°F). The warmest period often occurs right at the transition between dry and wet seasons, when intense solar radiation heats the landscape before the rains arrive to cool things down. Under the formal Köppen climate classification, a tropical savanna climate (labeled “Aw”) requires every month to average above 18°C (64°F) and at least two months to receive less than 60 millimeters (about 2.4 inches) of rain.
Where Rainfall Varies by Region
Not all savannas receive the same amount of rain. The global average sits around 80 to 150 centimeters (31 to 59 inches) per year, but some interior continental savannas get as little as 50 centimeters (20 inches). The type of vegetation that grows reflects these differences directly.
In Africa, drier savannas with fine-leaved, thorny trees and shrubs tend to appear in regions receiving just 200 to 500 millimeters of rain per year. These are the arid landscapes of the Sahel and parts of East Africa. Wetter, broad-leaved savannas with denser tree cover develop where rainfall reaches 800 to 1,300 millimeters annually. Asian savannas follow a similar pattern, though their fine-leaved zones tend to be slightly wetter, typically receiving 500 to 700 millimeters. Australian and South American savannas (the Brazilian cerrado being the largest) each have their own rainfall profiles, but the underlying pattern holds: more rain means more trees, less rain means more open grassland.
What the Dry Season Looks Like
The dry season is not simply a period without rain. It transforms the landscape. Surface water vanishes quickly as parched soils absorb any remaining moisture. Rivers shrink or disappear entirely. Grasses turn brown and brittle. Humidity drops sharply, and the combination of dry fuel, low humidity, warm air, and intense solar radiation creates ideal conditions for wildfire.
Fire is not an accident in savannas. It is a recurring feature of the climate. In many regions, a natural fire season emerges at the transition between the dry and wet periods. At that point, months of drought have left grasses and pine needles completely desiccated, and the first convective storms of the approaching wet season produce lightning strikes that ignite the landscape. In subtropical Florida’s pine savannas, for example, this fire window opens reliably every year when drought, low humidity, and the first lightning storms overlap. These fires burn across uplands and wetlands alike, clearing dead vegetation and recycling nutrients into the soil. Many savanna plants and trees have evolved thick bark, deep root systems, and the ability to resprout specifically because fire is a regular part of the climate cycle.
How Plants Survive the Drought
Savanna plants have developed precise strategies to cope with months of water scarcity. During extreme drought, trees and shrubs dramatically reduce the tiny pores on their leaves (stomata) to near-minimum levels, cutting water loss even though it also reduces photosynthesis. When atmospheric dryness pushes past certain thresholds, plants across different species and growth forms respond in remarkably similar ways, essentially shutting down their water exchange to protect their internal plumbing.
This is a deliberate tradeoff. By sacrificing leaf function, savanna plants keep water flowing through their stems and roots, preventing the kind of internal damage that would kill the plant outright. The strategy works: once rains return, leaf function and photosynthesis bounce back. This resilience is a direct product of the savanna’s predictable climate cycle. Plants have had millions of years to adapt to the rhythm of flood and drought, and the ones that survived are precisely tuned to it.
Climate Change Is Shifting the Pattern
The reliable wet-dry cycle that defines savannas is showing signs of disruption. In Brazil’s cerrado, the world’s most biodiverse savanna, researchers have documented a clear warming trend alongside declining rainfall. Between 2000 and 2019, precipitation dropped by an average of about 15 millimeters per year across studied locations, while evaporation rates increased by a similar amount. Some municipalities saw rainfall declines of nearly 13 millimeters per year.
The timing of the seasons is shifting too. In parts of the Brazilian savanna, the period of soil water loss now begins a month earlier than it did in the 1961 to 1990 baseline period. April, which once still had a slight moisture surplus, has shifted into the dry column. Drought conditions measured by standardized precipitation indices have intensified noticeably since 2010, with longer stretches of below-normal rainfall becoming the norm rather than the exception. These changes have serious implications for water availability, agriculture, and the fire cycle across tropical savannas worldwide.