Image credit: Nick Hill, SW Nova Biosphere Region

Originally published in SW Biosphere Region Spring/Summer Newsletter 2023.

Wetlands are incredible ecosystems for many reasons, and increasingly they have been acknowledged for their climate change mitigation and adaptation benefits, such as storing carbon and increasing community resilience. Yet, we also know wetland health and function are threatened by changes in temperature, precipitation, and extreme events. To make sense of the connections between wetlands and climate change, this article discusses how the climate is changing in Southwest Nova Scotia, what impacts climate change might have on wetlands in the region, and why wetlands are important for adapting to climate change.

Nova Scotia’s Changing Climate

While climate change is complex and multifaceted, the main expected changes for Nova Scotia can be summarized in five high-level trends: 

• Rising temperatures
• Changing precipitation patterns 
• More frequent and intense storms
• Rising sea levels
• Changing oceans 

Each of these trends has some relevance to wetlands, and so will be discussed in turn in the following paragraphs. The values referenced are the latest climate projections (CMIP6) for the geographic region of the Mersey River watershed, intended to be representative of the typical climate in Southwest Nova Scotia. Projections are for the period 2021-2050, relative to the historical average between 1971-2000. 

Over the next several decades temperatures may be 2.2°C higher, on average. This means hotter summers with a greater risk of heat waves, as well as conditions more likely to cause droughts or wildfires. Milder winter temperatures are becoming more common, impacting snow and ice cover; in Southwest Nova Scotia, the average winter temperature is anticipated to increase from -3.1°C historically to -0.6°C by mid-century. Warmer temperatures will extend the growing season by up to 30 days, which could be an opportunity for many plants, but also introduces new risks from pests, diseases, or invasive species that might be better adapted to these conditions than native plants. 

More precipitation is expected – about 7% more per year, on average, with most falling in winter and spring. However higher temperatures cause higher evapotranspiration rates, meaning more rain falling doesn’t necessarily result in more available moisture. Warmer temperatures also cause more precipitation will fall as rain rather than snow, and a trend towards more intense rainfall events. 

Intense tropical storms and hurricanes are anticipated to be more frequent, driven by warming oceans which enable these systems to maintain strength for much longer on their track north. These stronger storms will likely bring more powerful wind gusts and more extreme storm surges to Nova Scotia’s coasts. 

Concerns of coastal flooding are exacerbated by rising sea levels – approximately 75-80 cm of sea level rise is the median projection for Southwest Nova Scotia by 2100, under a high emissions scenario. These rising seas may also drive saltwater intrusion into coastal freshwater systems, and cause issues for sensitive coastal ecosystems such as salt marshes and dunes which may not be able to migrate quickly enough to keep pace. 

Ocean changes include increased temperatures, both at the surface and in deeper water, with marine heatwaves becoming longer and more frequent. Marine waters are becoming more acidic, causing challenges for aquatic life and increasing the likelihood of algal blooms. There is also a decreasing trend in marine oxygen levels, which can limit the growth and distribution of aquatic species. 

Climate change risks to wetlands

A few climate trends are specifically concerning for wetland health and function. Changing temperature and precipitation patterns could alter the hydrology of wetlands, with greater risks of both flooding and drought. The distribution of many species is also constrained by climate patterns, which are shifting; species towards the southern edge of their range are likely to face challenges in hotter summers, milder winters, and competition from species better adapted to more temperate climates. 

Rising seas may pose a threat to coastal wetlands, which may experience coastal squeeze and shrink over time if they don’t have space to move inland, limiting their benefits. More intense storms may cause erosion and damage to vegetation, which could be more difficult to recover from if large storms also occur more frequently. 

In the recent provincial climate change risk assessment, Weathering What’s Ahead: Climate Change Risk and Nova Scotia’s Well-being, wetland ecosystems were identified as a special area of concern. Wetlands are vital to our well-being now and in the future, but are at risk from multiple climate threats such as heat stress, shifting ecoregions, and invasive species. The provincial assessment identified that work is needed to better understand the specific vulnerabilities and opportunities of wetland ecosystems in Nova Scotia so as to ensure they are resilient to climate change. 

Of course, non-climate pressures such as development or pollution also pose risks to wetlands. Even in cases where climate change may not be the primary concern, climatic changes can often make it more challenging for these ecosystems to be resilient to the other pressures they face. 

The importance of wetlands for adaptation

All these concerns about risks to wetlands are underscored by the fact that abundant, healthy wetlands provide substantial benefits for adapting to the changing climate. Wetlands are effective natural sponges that slow, filter, and absorb stormwater to alleviate flooding, and by storing that water also ease the impacts of drought. 

Wetlands are very effective buffers against strong waves and storm surge, reducing erosion and protecting communities. A recent study in Nova Scotia found over 60% of incoming wave energy is dissipated within the first 10 metres of salt marsh for water depths less than one metre (Ngulube, 2021), which quantifies the shoreline protection healthy coastal wetlands provide. 

Wetlands are biodiversity hotspots that provide shelter and resources for abundant flora and fauna; they are incredibly effective carbon sinks, and store more carbon than any other ecosystem on Earth. Wetlands are sources of livelihoods, providing essential resources and services to support human wellbeing, including food, medicines, recreation, and cultural connections. 

Climate change is a growing threat to wetland ecosystems, and working to understand and address these potential impacts is a crucial step towards protecting and restoring these vital natural systems. The links between healthy wetlands and resilient communities are abundant, and deserving of greater recognition.