While global sea levels are rising, year after year, lakes around the world are shrinking. A recent IAEA study, published last week in Nature Communications, has revealed that many lakes are not able to compensate for water lost to evaporation and are at risk of disappearing over time.
"Global warming is a major threat to lakes' water budgets and quality because of rising temperatures, which enhance evaporation," says Yuliya Vystavna, first author of the study and Isotope Hydrologist at the IAEA. Given the range of variables that shape the history and life of a lake, quantifying the extent of climate change impact on lakes worldwide is a complex task that can be simplified with the use of nuclear science.
Lakes, which comprise the majority of global unfrozen surface freshwater resources, are an integral part of social and economic activities, as well as the ecosystem. When it comes to understanding the impact of climate change on lakes, isotope hydrology is a tell-tale tool for assessment. Lake parameters vary - from size, depth and surrounding land use to how they are created naturally or artificially - making it a challenge to objectively compare lakes on a global scale. However, "isotopes integrate all those parameters. Isotopes reveal the history of lakes and provide a record of change, serving as a proxy of hydrological history," Vystavna said.
Water loss through evaporation
A recent IAEA study analysed the stable isotope composition of more than 1000 lakes around the world to assess the impact of climate change on lakes. See the interactive map. (Image: Nature Communications)
The isotope analysis revealed that about one-fifth of water inflow in lakes around the world is lost to evaporation, and about 10 per cent of Earth's lakes show extreme evaporative losses - more than 40 per cent of total inflow. "Lakes sustain evaporation losses by inflow, but if a lake is losing more than 20 per cent of inflow, it is at risk of drying out," Vystavna said. "We used water balance models based on isotopes and estimated lakes' sensitivity to evaporation to determine which lakes around the world may disappear because they are not able to compensate for evaporation losses."
The team gathered information from databases, including the Global Network of Isotopes in Rivers, which includes data on rivers and lakes. In total, the stable isotope composition of 1257 lakes from 91 countries were analysed using artificial intelligence approaches developed by the IAEA. "We used artificial intelligence to determine what are the main evaporation drivers. Depending on climate type - tropical, arid, temperate, continental or cold - evaporation is driven by different factors," Vystavna said.
Regardless of the climate type, the amount of precipitation, wind speed, relative humidity and solar radiation affect the isotope composition of lakes and evaporation from them. The study showed that a combination of climatic and landscape variables, as well as lake size, need to be considered to predict lake evaporation processes.
"Understanding future availability of water resources is key to resilience, sustainable development and peace," said Johannes Cullmann, Director of Water and Cryosphere Coordination at the World Meteorological Organization (WMO). "Scientific isotope hydrological studies, as spearheaded by IAEA, are indispensable to underpin WMO's development of operational water assessment and forecasting systems."
The simple and affordable method of stable isotope monitoring creates potential for a global network of lake isotope data. "If you have a network dedicated to the collection and compilation of lake isotope information, you can provide explicit data and can compare and see climate change variations," Vystavna said.
