Â鶹ÒùÔº

Seasonal fluctuations to the climate are the dominant influence globally in shaping the changes to the size of lake surfaces, according to a new study.

The research, which has been in Nature, has "profound implications for greenhouse gas emissions, ecosystem health, and human livelihoods."

The collaboration between academics from Bangor University and Tsinghua University, in Beijing, China, achieved monthly mapping of 1.4 million lakes between 2001 and 2023. This was done by fusing datasets of satellite imagery, harnessing deep learning technology and combined high-performance computing, which tracked how lakes shrink and expand during the seasons.

While previous studies have focused on long-term changes, the ability to undertake comprehensive assessments of the impact of seasonality has previously been constrained by satellite data limitations.

The researchers found that lakes dominated by seasonality make up 66% of the global lake area and 60% of the total number of lakes. Over ninety percent of the world's population live in regions with such lakes.

During extreme events that are caused by seasonality, the impacts can exceed the combined magnitude of 23-year long-term changes and regular seasonal variations, doubling the contraction of 42% of shrinking lakes and fully offsetting in 45% of growing lakes.

Professor Di Long from Tsinghua University said, "Lakes are crucial for ecosystems, greenhouse gas emissions and water resources. Despite this, their surface extent dynamics, particularly seasonality, remain poorly understood at continental to global scales due to limitations in satellite observations.

"In our study we show that seasonality is the dominant driver of lake surface extent variations globally. These results uncover previously hidden seasonal dynamics crucial for understanding the responses of water systems to environmental changes, protecting lake systems, and improving global climate models."

Dr. Iestyn Woolway, a NERC Independent Research Fellow based at Bangor University's School of Ocean Sciences said, "Although some lakes show larger long-term trends than seasonality, our analysis indicates that the effects of seasonality-induced extremes can exceed the combined impact of long-term trends and typical seasonal fluctuations. These widespread and significant extremes have profound implications for greenhouse gas emissions, ecosystem health, and human livelihoods.

"Abrupt and drastic contractions in surface extent can expose sediments found at the bottom of lakes, potentially leading to significant methane releases.

"These extremes also modify the local climate and challenge the resilience of aquatic ecosystems, potentially destabilizing lake system food webs, altering the distribution of dominant primary producers, and precipitating critical, potentially irreversible ecosystem regime shifts, and affecting human well-being in the process.

"Our research shows the need for comprehensive monitoring and understanding of seasonality, which is essential for enhancing lake ecosystem protection, improving freshwater resource management, and refining global greenhouse gas budget estimates."