The Everglades is a unique, sprawling subtropical wetland in South Florida, and its entire existence is governed by the presence of water. Unlike most wetlands fed by deep rivers or large freshwater springs, this ecosystem is sustained almost entirely by atmospheric moisture. The quantity and timing of precipitation are the single most important metrics for the region’s health. The annual cycle of rainfall dictates the rhythm of life for every plant and animal species that calls this national park home.
The Specific Annual Rainfall Average
The Everglades receives a substantial amount of precipitation each year, averaging between 50 and 65 inches (127 to 165 centimeters) across the region. The Eastern Coastal Ridge areas often record the higher end of this range, sometimes receiving nearly 62 inches of rain annually. Conversely, the areas closer to Lake Okeechobee, which historically fed the system, tend to receive slightly less, sometimes closer to 48 inches per year. The sheer volume of this annual rainfall demonstrates the tropical character of the climate, providing the necessary input to maintain a permanently saturated environment.
The Dramatic Seasonal Distribution
The annual rainfall does not fall evenly throughout the year, but is concentrated into two distinct seasons: a wet season and a dry season. The wet season typically runs from mid-May through October, delivering the majority of the year’s total precipitation. During this time, approximately 70% to 75% of the total annual water falls. This intense period of rain is primarily delivered through daily, localized convective thunderstorms and, less frequently, by tropical storms or hurricanes.
The dry season, which lasts from November through April, is characterized by much lower precipitation totals. Only about one-quarter of the annual rainfall occurs during these cooler months. The weather patterns shift from convective storms to frontal systems, which bring cooler, drier air that suppresses most shower activity.
How Rainfall Shapes the Everglades Ecosystem
The massive influx of water during the wet season is what creates the famous hydrological feature known as the “River of Grass.” This precipitation sustains a vast, slow-moving sheet of water that flows imperceptibly southward over a shallow limestone base. The sustained water depth dictates the location and composition of plant communities, such as the extensive sawgrass marshes and the higher-elevation tree islands.
The annual rise and fall of the water level are the driving forces behind the life cycles of the native fauna. During the wet season, the water sheet expands, providing breeding grounds for aquatic prey species like fish and amphibians. As the dry season progresses and the water recedes, these prey animals become concentrated in deeper sloughs and pools. This concentration makes them easier targets for wading birds, alligators, and other predators, forming the foundation of the Everglades’ seasonal food web.
Factors Driving Rainfall Variability
The actual amount of precipitation can vary significantly from year to year due to large-scale climate patterns. Natural cycles like the El Niño-Southern Oscillation (ENSO) have a strong influence on the South Florida climate. El Niño events are often associated with increased rainfall and a wetter season, while La Niña phases typically lead to prolonged periods of drier weather and drought conditions.
Beyond these natural oscillations, the intensity and distribution of the rainfall are also being influenced by human impacts. Climate change is a factor, as rising temperatures can alter evaporation rates and the intensity of extreme storm events. Furthermore, human intervention in the form of massive water management structures, including canals, pumps, and the Herbert Hoover Dyke, has fundamentally changed how precipitation is distributed. These structures divert water away from the natural flow path, reducing the amount of water actually available to sustain the historic River of Grass.