Unveiling the Global Decline in Lake Water Storage: Causes, Consequences, and Solutions

Lakes, covering approximately 3% of the global land area, play an important role in providing essential ecosystem services, including the supply of fresh water and food, waterbird habitat, pollutant and nutrient cycling, and recreational opportunities. Moreover, they significantly impact biogeochemical processes and climate regulation through carbon cycling. However, the sustainability of these vital natural resources is under threat due to fluctuations in lake water storage (LWS), influenced by various factors such as precipitation changes, river discharge, human activities (like damming and water consumption), and climate change.

The estimation of global LWS trends has been a complex undertaking, hampered by limitations in both modeling and observational capabilities. Current global hydrologic models often neglect LWS changes or use oversimplified one-dimensional models of lake volume changes. In situ lake measurements are sparse and often have irregular temporal coverage. Satellite observations, while crucial for assessing large-scale LWS variability, are limited by sensor constraints, such as coarse resolution, infrequent overpasses, and mission gaps. These limitations have made it challenging to attribute decadal-scale LWS variability accurately.

In a new study recently published in the peer-reviewed Science Journal, authored by Dr. Fangfang Yao, Dr. Ben Livneh, Dr. Balaji Rajagopalan from the University of Colorado Boulder, Dr. Jida Wang from Kansas State University, Dr. Jean-François Crétaux from Université de Toulouse, Dr. Yoshihide Wada from the International Institute for Applied Systems Analysis (IIASA), and Dr. Muriel Berge-Nguyen from the Centre National d’Études Spatiales (CNES). The research team constructed a comprehensive global database of time-varying LWS from 1992 to 2020 to understand the trends and drivers of global LWS changes, the implications of these changes, and potential solutions for sustainable water resource management. This database includes sub-yearly storage time series for 1,972 large water bodies, comprising both natural lakes and reservoirs. Leveraging recent advances in algorithms and cloud-based parallel computing, the team used one-quarter million Landsat satellite images to construct time-varying water areas for these lakes. They estimated lake volume variability by combining water areas with water surface elevation measurements from various satellite altimeters. This approach yielded a detailed and comprehensive dataset on LWS changes.

To estimate lake volume variability, the researchers combined the water areas obtained from satellite imagery with water surface elevation measurements from various satellite altimeters, including CryoSat-2, ENVISAT, ICESat, ICESat-2, Jason series 1-3, SARAL, and Sentinel 3. This integration allowed them to determine how the water storage in these lakes changed over time. The researchers’ findings reveal a widespread decline in global LWS over the past 28 years. More than half of the large lakes experienced significant water losses, affecting major regions worldwide, including Central Asia, the Middle East, India, China, Europe, Oceania, the United States, Canada, Africa, and South America. In contrast, about one-quarter of the large lakes experienced significant water gains, primarily in regions with extensive dam construction or remote, sparsely populated areas. Globally, the research indicates a net decline in LWS at a rate of approximately -21.51 ± 2.54 gigatons per year, equivalent to 602.28 cubic kilometers in cumulative volume. This loss in LWS is significant, highlighting the substantial impact on the global water cycle and freshwater resources.

The study goes further to attribute the LWS trends in natural lakes and reservoirs to various factors. For natural lakes, 56 ± 9% of the decline is attributed to human activities and changes in temperature and evaporative demand, i.e., measuring how ‘thirsty’ the atmosphere is. In contrast, 24% of natural lakes experience significant water gains due to regional increases in precipitation and runoff. The remaining change in LWS is linked to changes in precipitation, runoff, sedimentation, and human water use, depending on the specific lake. For reservoirs, over 80% of existing reservoirs experience significant storage declines, primarily due to sedimentation, i.e., a process in which reservoir storage capacity is replaced by sediment from incoming rivers. Sedimentation-induced reservoir storage capacity loss largely offsets the storage gains from new dam construction. Droughts also contribute to reservoir storage declines in some regions. The study differentiates between arid and humid regions, highlighting that arid regions experience a net storage decline for both natural lakes and reservoirs. Human water consumption, temperature, and PET changes, as well as reduced natural flows, contribute to these declines. In humid regions, new reservoir construction offsets storage declines in existing reservoirs, driven by a dam construction boom in specific basins. Nevertheless, a substantial portion of both natural lakes and reservoirs in humid regions experiences storage declines.

The researchers’ findings have significant implications for water resource management, particularly for the billions of people residing in basins with large water bodies experiencing significant water storage losses. Such losses can have far-reaching consequences, including reduced freshwater availability, environmental degradation, and decreased hydropower energy production. Moreover, sedimentation in existing reservoirs poses a significant challenge for sustainable freshwater supplies and requires careful consideration in reservoir operations and the construction of new dams. Human activities, including water withdrawal and climate change-induced temperature and evaporation changes, play a crucial role in LWS decline, underscoring the need for effective water conservation efforts and long-term planning.

Understanding the trends and drivers of global LWS changes is crucial for effective water resource management. Lakes are essential sources of freshwater for human consumption, agriculture, and industry. Recognizing the factors contributing to LWS decline can inform sustainable water management practices, particularly in regions heavily reliant on lakes for their water supply. Moreover, many large lakes are important ecosystems that support diverse flora and fauna. Identifying the factors leading to LWS decline helps in assessing the potential impact on these ecosystems. Conservation efforts can be directed towards mitigating the negative consequences of LWS changes, such as habitat loss for waterbirds and disruptions in nutrient cycling. The study provides valuable insights into the impact of climate change on LWS. Rising temperatures, changes in precipitation patterns, and altered potential evapotranspiration are all factors that contribute to LWS decline. The new study adds to the growing body of evidence linking climate change to alterations in Earth’s hydrological cycle.

In conclusion, the authors highlighted the role of human activities in LWS changes. Factors like dam construction and unsustainable water consumption were found to significantly affect LWS, particularly in arid regions. Recognizing the human footprint on these changes is essential for informed decision-making and sustainable development. The research identifies that a substantial portion of the global population resides in regions where large water bodies are experiencing significant LWS losses. These findings underscore the potential societal impacts of declining LWS, including challenges related to water supply, environmental degradation, and energy production. By constructing a comprehensive global database of LWS changes over nearly three decades, the study highlights the importance of long-term monitoring. This dataset can serve as a valuable resource for future research on climate change, hydrology, limnology, and water resource management.  The study’s findings can guide policy and planning efforts related to water resource management and environmental conservation. Governments and organizations can use this information to develop strategies aimed at mitigating LWS decline and its associated consequences.