Lakes are a crucial source of Earth's freshwater, providing various ecosystem and socioeconomic services. They offer water and food supply, habitats for waterbirds, nutrient cycling, recreational activities, navigation, and hydropower generation. The usesof lakes are heavily influenced by their water volumes, which can be affected by changes in precipitation, river inflow, and evaporation. There have been significant shifts in lake levels, as seen in the Aral Sea and Lake Mead, indicating the growing threats from climate change and human activities.

One important question is: “are drying lakes limited to specific regions or is this a global trend?”. However, it is challenging to obtain data on the variation of a lake’s water level over time, especially on a global scale. In-situ measurements are mainly concentrated in certain areas, and satellite altimeters have limited spatial and temporal coverage, hindering consistent analysis of global-scale trends. 

To address this issue, we developed a new method to generate near-monthly water storage data for all large water bodies worldwide over the past three decades. We combined short-term level measurements from recent altimeters with longer-term water areas mapped from historical satellite images. This allowed us to reconstruct water levels over the course of several decades on a global scale. By applying this novel approach to nearly 250,000 satellite images and water level measurements from altimeters, we were able to provide a comprehensive view of lake water storage trends in the 1,972 largest lakes on Earth. 

To understand the reasons behind water losses or gains in lakes, we identified three key factors. First, we analyzed ‘natural’ changes by examining precipitation and river flow, which are primarily influenced by natural climate variability. Secondly, we investigated the impacts of climate change by studying temperature and evaporative demand, i.e., measuring how ‘thirsty’ the atmosphere is. Lastly, we considered human water consumption by incorporating data from models. Using statistical techniques, we modeled the response of lake volume variability to changes in these climate and human variables. 

Our findings indicate that 53% of Earth’s large water bodies experienced drying between 1992 and 2020. What is surprising is that this phenomenon occurred not only in arid regions but also in humid regions. Previous climate studies indicate a “dry-get-drier and wet-get-wetter” pattern in a warming climate. This is widely recognized in observations and models.  Our study confirms a “dry-get-drier” pattern in lake water storage. However, we also observed widespread lake water losses in the humid tropics and high latitude regions over the last three decades, suggesting that drying lakes worldwide are more extensive than previously thought, certainly concerning lake water storage. 

More than half of the total water loss in natural lakes can be attributed to both warming and increased human water consumption. Therefore, the widespread global declines in lake water storage may signify global aridification under warming and increasing human water use. Additionally, our study reveals that sedimentation dominated the total water loss in existing reservoirs filled before 1992. Sedimentation is an ongoing, slow process that gradually reduces the capacity of reservoirs to store water, thereby becoming less reliable for freshwater and hydroelectric energy supply. Reservoir sedimentation rates can accelerate under climate change due to increasing extreme precipitation, as well as land disturbances such as wildfires, landslides, and deforestation. 

By providing new insights into the extent of changes occurring in global lakes, our study aims to raise awareness about this issue. It is important to note that approximately a quarter of the global population lives in a basin with a large, drying lake. The potential impacts of drying lakes, such as freshwater shortages, environmental degradation, and hydropower energy reduction, can be significant. Therefore, it is crucial to manage lakes effectively to maintain healthy levels in order to mitigate the impacts, ensuring long-term sustainability.