- ESA missions help to reveal wo...
ESA missions help to reveal worldwide lake water loss trend
29 Jun 2023
Climate change, human consumption and sedimentation are depleting more than half of the world’s biggest lakes of water, according to a ground-breaking analysis that drew on three decades of satellite data.
The study – published in the journal Science – estimates that about 25% of the global population now lives in the basin of a large, drying lake, highlighting the urgent need to improve the sustainable management of these shrinking water bodies.
In the past decades, observations have shown that the volume of many individual lakes is reducing but, until now, no study has established whether this alarming trend holds true on a global scale.
Since in-situ measurements are limited in their temporal and spatial coverage, scientists used satellite data to complete a worldwide, long-term study of lake water storage.
The researchers used some 250,000 images delivered by the US Landsat programme, which have a resolution of 30 m. Covering 1992 to 2022, these data captured nearly 2000 of the world’s largest lakes.
By observing this optical imagery, the team calculated changes in lake surface area over time, and to determine lake water levels they turned to altimetry data.
Satellite altimetry missions are able to estimate the surface level of water bodies by emitting radar pulses and timing how long it takes for them to bounce back to the mission’s receiver.
The study drew on altimetry data from CryoSat and Envisat, as well as seven other missions, including NASA’s ICESat satellites and Copernicus Sentinel-3.
Hosting one instrument named the SAR/Interferometric Radar Altimeter (SIRAL), CryoSat launched in 2010, and is planned to remain active until at least 2025.
Envisat – which carried the Radar Altimeter 2 (RA-2) instrument – began operations in 2002, delivering a decade of data before the mission concluded in 2012.
Altimetry missions covered the majority of the target lakes for the entire study period. In other cases, lake water levels were available for a limited time, or depth profiles were used.
To calculate lake volume, the researchers looked at how the relationship between lake water level and lake surface area changed over time.
After analysing nearly 2000 lakes, the team found a net decrease in water storage of around 22 billion tonnes across the whole dataset.
These losses impacted lakes in both dry and humid environments, but there were also some exceptions to the trend.
Artificial reservoirs, for example, increased in volume due to a rise in the number of these water bodies constructed during the study period.
Focusing on natural lakes, the scientists then delved into the causes of this water loss by investigating five known drivers of lake drying: temperature, precipitation levels, water run-off from surrounding areas, potential evapotranspiration, and human water consumption.
A modelling approach was employed that drew on datasets related to these variables.
From this analysis, it was found that more than half of the losses from natural lakes were at least partially a consequence of climate change. This included declines resulting from increases in temperature and evapotranspiration, as well as some decreases in run off.
The team also uncovered unsustainable human consumption as novel driver of shrinking lake volume.
In addition, several examples of the positive impacts of sustainable lake management strategies on lake water volumes were discovered.
Water losses were partially recovered in Lake Sevan in Armenia, for instance, after officials passed legislation to limit withdrawals for irrigation.
The study was led by scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES) of the University of Colorado in the US.
Fangfang Yao et al., Satellites reveal widespread decline in global lake water storage. Science 380, 743-749 (2023). DOI: 10.1126/science.abo2812.