Seasonal Changes Dominate Global Lake Surface Size Fluctuations, New Study Finds

A new study published in Nature reveals that seasonal climate fluctuations are the primary factor driving changes in the surface area of lakes globally. This finding has profound implications for greenhouse gas emissions, ecosystem health, and human livelihoods. The study, a collaborative effort between Bangor University and Tsinghua University in Beijing, China, mapped the surface extent of 1.4 million lakes each month from 2001 to 2023. By merging satellite imagery and employing deep learning and high-performance computing, the researchers were able to track the expansion and contraction of lake surfaces throughout various seasons. Earlier studies often focused on long-term trends, but the ability to conduct a thorough assessment of seasonal impacts was limited by the availability of satellite data. The current findings show that 66% of the global lake area and 60% of all lakes are significantly influenced by seasonal variations. Moreover, over 90% of the world's population resides in regions where these seasonal impacts are pronounced. The researchers discovered that during extreme seasonal events, the effects can surpass the combined magnitude of both 23-year long-term changes and regular seasonal fluctuations. Specifically, these events can double the contraction of 42% of shrinking lakes and completely offset the growth observed in 45% of expanding lakes. Professor Di Long from Tsinghua University emphasized the importance of this research. "Lakes play a critical role in ecosystems, greenhouse gas emissions, and water resources," he said. "However, our understanding of the dynamics of lake surface extent, especially concerning seasonality, has been hindered by limitations in satellite observations. Our study reveals that seasonality is the dominant driver of lake surface extent variations on a global scale. These findings are crucial for comprehending how water systems respond to environmental changes, protecting lake ecosystems, and enhancing global climate models." Dr. Iestyn Woolway, a NERC Independent Research Fellow at Bangor University's School of Ocean Sciences, added, "While some lakes exhibit more pronounced long-term trends than seasonal variations, our analysis shows that the impact of seasonality-induced extremes can outstrip the combined effect of long-term changes and typical seasonal fluctuations. These widespread and significant extremes have far-reaching consequences for greenhouse gas emissions, ecosystem health, and human well-being." One key consequence of these seasonal changes is the exposure of sediments at the bottom of lakes, which can lead to significant releases of methane, a potent greenhouse gas. Additionally, the extremes associated with seasonal fluctuations can alter local climates and challenge the resilience of aquatic ecosystems. This can destabilize food webs, change the distribution of primary producers, and trigger critical, potentially irreversible ecosystem shifts that affect human welfare. The research underscores the necessity of continuous and comprehensive monitoring of seasonal lake dynamics. Such monitoring is vital for improving the protection of lake ecosystems, managing freshwater resources effectively, and refining global greenhouse gas budget estimates. By better understanding these seasonal variations, scientists and policymakers can develop more informed strategies to mitigate the impacts of environmental changes on lakes and the communities that depend on them.