When a lake shrinks, what is causing it? A new method looks for the answer

Istanbul, Türkiye – A shrinking lake's visibility is obvious, but understanding its causes is more complex. Changes such as less rainfall, higher temperatures, and evaporation can impact a lake, as can irrigation, urban expansion, agriculture, and dams that modify water inflow. Often, multiple factors occur simultaneously. Researchers have created a method to synthesize these clues and identify the main drivers of lake changes across a whole country. Using Türkiye's lakes as a case, the Lake Assessment Methodology (LAM) combines satellite data with climate, land use, lake depth, altitude, water type, human activity, and other factors. Instead of just showing where water has gone, this approach aims to help scientists and water managers explore what might be causing the change. The study, published in Water and Environment Journal, was conducted by researchers from Istanbul Technical University, Yildiz Technical University, and Stantec UK Limited. 

From detecting change to investigating its cause

Satellite remote sensing has greatly enhanced scientists' ability to monitor lakes, revealing changes in lake area, water level, and storage worldwide. Research has shown these changes are influenced by both climate change and human activities. A broader study published in Science analyzed nearly 2,000 large lakes and reservoirs globally, finding significant water storage declines in 53% of them from 1992 to 2020. Major causes include climate warming, increased evaporation, and human water use.

The new study tackles a different challenge: how to organize various types of evidence into a practical assessment that identifies the main pressures affecting individual lakes across a country. Researchers started with an inventory of 302 natural lakes in Türkiye. Due to satellite image resolution, they focused on 27 lakes larger than 2,000 hectares, analyzing long-term changes from 1985 onward. They created a Lake Information Database covering seven categories: water type, meteorological data, altitude, beneficial use, land use and cover, depth, and protection status. The framework also includes data from official sources and examines infrastructure like dams on rivers feeding these lakes. By evaluating this information alongside changes in water surface area, researchers aim to determine if climatic factors, human influence, or both are the main drivers.

“Seeing that a lake has become smaller is only the beginning of the question,” said Professor Aysegul Tanik of the Department of Environmental Engineering at Istanbul Technical University’s Faculty of Civil Engineering. “We wanted to bring together the different pieces of evidence so that researchers and decision-makers can better understand what may be driving the change and where management attention may be needed.”

Three lakes, three different stories

The researchers demonstrate their approach through three lakes with distinct characteristics: freshwater İznik Lake, brackish Burdur Lake, and saline Tuzla Lake. Using satellite images from Landsat 5 and Landsat 8, they analyzed changes in water surface areas from 1985 to 2020. The differences were notable. İznik Lake remained relatively stable, with only about a 1% reduction in water surface area over the period. Despite surrounding changes, its water budget seemed fairly balanced. In contrast, Burdur Lake experienced a 39.79% decrease in surface area. The team linked this decline primarily to human activities like dam construction and land-use changes, alongside climatic pressures, by studying land use, climate data, and upstream water infrastructure. Tuzla Lake also saw significant reductions, with climate factors, especially rising temperatures, playing a larger role than human influences, likely due to its higher altitude. Overall, the study revealed a pattern: lakes at lower altitudes were more affected by human activities, while higher-altitude lakes were more influenced by climate. Shallow lakes also showed greater surface area changes than deeper ones. Though these altitude-based patterns are not universal, they align with previous observations elsewhere and demonstrate how this methodology integrates environmental and human factors into assessments.

“Two lakes can both be losing water, but for very different reasons,” Tanik said. “That distinction matters because the response should differ. A lake primarily affected by local water use may require different management actions than one whose changes are dominated by climatic conditions.”

A framework designed to travel

An important strength of LAM lies in its adaptability. The researchers designed the database so that assessment categories can be added or removed based on the available information in a specific country or region. This makes the approach especially valuable where detailed hydrological models or extensive ground-monitoring networks are lacking, but satellite imagery and basic environmental and land-use data can be collected. However, the authors acknowledge key limitations. The current study focused on natural lakes larger than 2,000 hectares and did not include water quality or lake bathymetry, nor did it project future changes. They suggest that future research could expand the method to smaller lakes and reservoirs, incorporate water quality and lake-depth data, and apply statistical or multi-criteria decision analysis to better quantify climate and human impacts. They emphasize the need for further statistical analysis to distinguish climate change effects from human activities and to better address uncertainties.

For communities near a shrinking lake, the core question is practical: understanding how much water has been lost indicates that change is happening, and identifying likely causes can guide action. By converting satellite images, climate data, maps, and human activity information into a unified assessment framework, the researchers hope LAM can advance lake monitoring, from simply observing water loss to understanding the underlying pressures behind it.