Grasslands exist in a climate sweet spot: too dry for forests, too wet for deserts. They typically receive 500 to 950 millimeters (20 to 35 inches) of rain per year, compared to less than 300 mm in deserts and more than 2,000 mm in tropical forests. Temperatures swing widely depending on latitude, ranging from as low as -20°C (-4°F) in winter to 30°C (86°F) in summer. But rainfall alone doesn’t tell the whole story. Wind, fire, and seasonal drought patterns all shape where grasslands form and how they persist.
Temperate Grassland Climate
Temperate grasslands, which include the North American prairies, the South American pampas, and the Eurasian steppes, experience cold winters and warm summers. Annual rainfall is moderate, typically between 30 and 50 centimeters, with most of it falling in late spring and early summer. That concentrated rainfall creates a burst of green growth followed by months of brown dormancy as moisture dries up through fall and winter.
The temperature extremes in these regions are significant. Winter lows can drop well below freezing, while summer highs regularly climb past 30°C. This range means temperate grasslands deal with both frozen ground in winter and heat-driven evaporation in summer, keeping soil moisture levels fluctuating throughout the year. The combination of limited rainfall and high evaporation prevents trees from establishing in most areas, giving grasses the competitive edge.
Tropical Grassland Climate
Tropical grasslands, commonly called savannas, are warmer year-round and receive more rain than their temperate counterparts, typically between 76 and 100 centimeters per year. The defining feature of savanna climate is its sharp division into wet and dry seasons. The dry season can last anywhere from 3 to 8 months, during which very little rain falls and temperatures remain high. The wet season then delivers heavy, concentrated rainfall that saturates the soil and fuels rapid plant growth.
This seasonal rhythm shapes everything about savanna ecosystems. Grasses grow tall and fast during the rains, then dry out and become highly flammable fuel during the dry months. Unlike temperate grasslands, where cold is the main stress, tropical grasslands challenge plants with prolonged drought and intense heat. Trees that do survive in savannas tend to be widely spaced and adapted to fire, rather than forming the dense canopy you’d find in a tropical forest.
Why Wind Matters as Much as Rain
One of the less obvious forces shaping grassland climate is wind. Research on North American grasslands found that wind speed was the single most influential factor in predicting where grasslands occur, outranking precipitation, humidity, and evaporation rates. Wind speeds of about 4.5 meters per second (roughly 10 miles per hour) at 10 meters above ground consistently marked the boundary of grassland regions.
Wind matters because it drives fire. Grasslands are fire-dependent ecosystems, and strong, steady winds allow fires to spread across vast, flat terrain, burning back any trees or shrubs that try to establish. Without frequent fire spread by wind, many grassland areas would gradually transition into forest or shrubland. These wind boundaries have remained remarkably stable over thousands of years, shifting only slightly northward over the past 11,000 years.
The Role of Seasonal Drought
Both temperate and tropical grasslands experience a period each year when water is scarce. In temperate grasslands, this comes during late summer and fall when rainfall tapers off and evaporation peaks. In tropical savannas, it’s the dry season that can stretch more than half the year. Either way, the recurring drought cycle is what keeps grasslands as grasslands.
Grasses survive these dry periods by investing heavily in their root systems. When conditions turn dry, the visible blades above ground go dormant or die back, but the roots stay alive underground, ready to regrow when moisture returns. This strategy gives grasses a major advantage over trees, which need consistent moisture to maintain their large above-ground structures. Climate factors like rainfall timing and amount influence how much plant growth occurs above versus below the surface, with drier conditions pushing more energy underground.
Soil also plays a role in buffering these dry spells. Research in steppe grasslands has shown that the soil’s ability to retain water is actually a stronger predictor of how much organic carbon the soil stores than the climate itself. In other words, two grassland sites with the same rainfall can have very different soil richness depending on how well their soil holds onto moisture between rains.
How Grassland Climate Differs by Region
Not all grasslands experience the same version of this climate pattern. The North American prairies get most of their rain in late spring and early summer, with relatively dry winters that are bitterly cold. The South American pampas share a similar rainfall range but experience milder winters due to their latitude and proximity to the ocean. The Eurasian steppes tend to be the driest and most continental of the temperate grasslands, with harsh winters and limited rainfall that keeps vegetation short and sparse.
Tropical savannas in Africa, South America, and Australia sit closer to the equator, where temperatures stay warm year-round but rainfall follows a strict on-off seasonal pattern. African savannas in particular experience some of the longest dry seasons, stretching up to 8 months in some regions. Australian tropical grasslands face a similar seasonal split but also contend with extremely high temperatures during the wet season, which accelerates evaporation and limits how much of the rainfall actually benefits plants.
What Separates Grasslands From Forests and Deserts
The simplest way to understand grassland climate is by its position between two extremes. Below about 300 mm of annual rainfall, there isn’t enough water to sustain continuous grass cover, and the landscape becomes desert or scrubland. Above roughly 950 to 1,000 mm, there’s enough moisture for trees to outcompete grasses and form forests. Grasslands occupy the band in between, where rain is sufficient for grasses but not enough (or not consistent enough) for dense tree growth.
Fire and wind reinforce this boundary. Even in areas where rainfall could theoretically support trees, frequent fires carried by strong winds keep woody plants from gaining a foothold. This is why some ecologists describe grasslands not just as a climate-driven biome but as a fire-maintained one. Remove fire from the equation, and many grasslands would slowly become woodlands, regardless of the rainfall they receive.