The Everglades, often called the “River of Grass,” is a unique wetland ecosystem in South Florida. Its existence is entirely dependent on its distinct climate, which dictates the flow and depth of water across the region. The climate is characterized by year-round warmth and a dramatic shift between two primary seasons, driving the hydrological and ecological cycle.
Defining the Subtropical Climate
The climate of the Everglades is officially classified as subtropical, bordering on tropical conditions. This designation results from minimal annual temperature variation and the absence of a true winter season. Average monthly temperatures range from a low around 65°F in January to a high near 83°F in July.
Winter high temperatures typically fall between 70°F and 79°F. Humidity remains a dominant factor throughout the year, especially during the summer months when dew points are consistently high, often pushing levels above 90%.
The Annual Cycle of Wet and Dry Seasons
The most defining characteristic of the Everglades climate is its annual cycle, which is divided starkly into a wet season and a dry season. This seasonal shift, rather than temperature change, controls the life and health of the entire ecosystem. The wet season typically spans from May or June through October or November, delivering approximately 70% of the annual rainfall.
Wet season rainfall is largely convective, meaning it arrives through brief but intense daily afternoon thunderstorms. These tropical downpours cause water levels to rise significantly, resulting in the sheet of water that gives the Everglades its famous “River of Grass” nickname. High temperatures, often exceeding 90°F inland, combine with the heavy rainfall to create an environment of intense heat and humidity.
The dry season lasts from November or December through April or May. The weather is characterized by lower humidity, clearer skies, and less frequent precipitation. Any rain that does occur is often associated with the passage of cold fronts that occasionally dip down from the north.
The drop in rainfall causes water levels to recede dramatically, leading to the concentration of aquatic life in deeper pools and sloughs. This concentrated food source triggers the nesting season for many wading birds and attracts migratory species. The cycle of flooding and recession is the natural pulse of the Everglades.
The Influence of Extreme Weather Events
The Everglades is subject to irregular, high-impact weather events. Tropical storms and hurricanes are the most dramatic, posing a significant threat primarily during the late summer and fall. These events deliver massive amounts of rain over a short period, and coastal areas are vulnerable to severe storm surge.
The coastal mangrove forests, which buffer against wind and wave action, can suffer extensive damage from major storms. For instance, Hurricane Irma in 2017 caused an estimated 60% dieback of mangroves in the 10,000 Islands region. Such intense disturbances leave a lasting signature on the ecosystem, with researchers finding that chemical changes in the water from these events can be detected for many years afterward.
The Everglades occasionally experiences cold snaps and rare freezes, particularly in the northern reaches. While frost is rare in the southernmost areas, temperatures may still drop into the 30s or low 40s a few times each decade. These cold events are ecologically significant because they can temporarily knock back populations of non-native, cold-intolerant species, such as the Burmese python, which have invaded the ecosystem.