A wetland is an area of land saturated by water, either permanently or seasonally, which creates a distinct ecosystem unlike terrestrial or deepwater environments. The climate experienced within a wetland is a direct result of the continuous interplay between the water present and the surrounding atmosphere. This interaction creates unique microclimatic conditions that moderate local weather and support specialized plant and animal life. Understanding the climate of a wetland means examining how water moves through the system, how temperature is regulated, and how global climate zones dictate the specific wetland type.
The Unique Role of Hydrology
The presence of standing or saturated water establishes a specific microclimate that differs from adjacent dry areas. The overall water budget, or hydroperiod, of a wetland is determined by the balance between water input and output. Input sources include direct precipitation such as rain or snowmelt, surface runoff, and subsurface groundwater flow, while the primary output is evapotranspiration, the combined loss of water through surface evaporation and plant transpiration.
The constant presence of water ensures a high atmospheric moisture content, resulting in humidity levels significantly greater than those found in nearby uplands. This moisture-rich atmosphere is fundamental to the wetland climate. The saturation frequency, whether permanent as in swamps or seasonal as in prairie potholes, dictates the duration of these humid conditions and influences the development of anaerobic soil conditions, which restrict oxygen availability and shape the resident plant and microbial communities.
Temperature Regulation and Extremes
Wetlands exhibit moderated temperatures due to the high heat capacity of water (thermal inertia). Water heats and cools much slower than air or dry land, stabilizing the environment. This moderation leads to a smaller diurnal, or day-to-night, temperature range within the wetland compared to surrounding terrestrial areas.
While the thermal inertia generally provides a cooling effect in tropical regions, the temperature dynamics can become complex in colder zones. In boreal wetlands, for instance, the large water storage can absorb energy during summer, but release it during winter, sometimes resulting in a warming effect on the local land surface temperature during the colder months. Freezing is a significant temperature extreme in high-latitude wetlands, where the long-term cold temperatures and saturated conditions lead to very slow decomposition rates and the build-up of peat.
Global Climatic Zones Defining Wetland Types
Wetland ecosystems are distributed globally and are shaped by the macroclimate of their region. The broad classification of a wetland is often determined by the prevailing temperature and precipitation patterns of its climatic zone. Different zones produce distinct wetland types with unique hydrological and thermal characteristics.
Boreal wetlands, such as bogs and fens, are concentrated in the cold northern latitudes where low temperatures and high moisture result in minimal evaporation and the accumulation of thick peat layers. Conversely, tropical wetlands, which include extensive mangrove swamps, are defined by consistently high heat, abundant precipitation, and year-round high humidity. Temperate wetlands, such as many freshwater marshes, experience a climate characterized by distinct seasonal temperature shifts and varied precipitation patterns, leading to cycles of high and low water levels.
Climate Change Effects on Wetland Health
Rising average global temperatures and shifts in the timing and amount of precipitation are expected to change the fundamental hydroperiod of many wetlands. This can result in more frequent or severe drying in some regions, while others may experience excessive flooding, pushing the ecosystem past its tolerance limits.
Coastal wetlands face the impact of sea level rise, which drives saltwater intrusion into freshwater systems. This intrusion changes the soil chemistry, making the environment unsuitable for existing freshwater plants and microbes and potentially converting vegetated areas into open water mudflats. Furthermore, the warming and drying of wetland soils can cause the release of stored carbon back into the atmosphere, creating a negative feedback loop that further contributes to global climate change.