From Romania to Kazakhstan, summer droughts linked to less winter ice in two rapidly warming seas

This summer, Europe experienced one of the most severe droughts in over four centuries, marked by scarce rainfall and frequent heatwaves. While western Europe faced significant wildfires, eastern Europe, especially due to the ongoing war in Ukraine, was also severely affected. Studies suggest that such droughts will become more frequent and intense due to human-induced global warming. Researchers are now investigating whether winter sea ice cover could serve as an early indicator of summer drought risk.

The study, published in Frontiers in Water, suggests a direct link between reduced winter sea ice in the Barents and Kara seas, located in the Arctic, and increased summer drought across a vast region in Eurasia, stretching from eastern Romania, Moldova, and Ukraine to western Kazakhstan. Lead author Dr. Petru C. Vaideanu of the University of Bucharest, Romania, explained that a winter with significantly less sea ice than usual may signal a higher likelihood of drought in these areas during the following summer.

The researchers focused on the Barents and Kara seas due to their substantial reductions in winter sea ice since the 1980s. If no measures are taken to reduce CO₂ emissions, simulations predict that by the end of this century, sea surface temperatures in these regions could rise by 4°C to 5°C. This rapid warming is attributed to various factors, including increased warm water from the Atlantic entering the area, local feedbacks caused by decreasing sea ice, changes in cloud formation, and other atmospheric processes.

To investigate the potential link, the researchers analyzed historical records of sea ice in the Barents and Kara seas from October to March. They utilized ERA5, a database from the European Center for Medium-Range Weather Forecasts, which integrates observations with a weather model to estimate average atmospheric conditions across Eurasia since 1940.

The team calculated drought conditions by examining precipitation records and potential evapotranspiration estimates for the period from May through September, reflecting below-average rainfall or increased atmospheric demand for moisture. They also adjusted for the long-term increase in atmospheric CO₂ levels, as both sea ice coverage and summer drought can change in response to warming climate, potentially creating a false correlation.

The analysis revealed evidence that a reduction in winter sea ice is likely an important driver of summer drought, rather than just an association. The researchers found that winters with less sea ice in the Barents and Kara seas were followed by a more bent atmospheric circulation pattern over the North Atlantic and Eurasia. Such bending of the atmosphere could bring warmer, drier air into the identified drought corridor in Eurasia, causing stagnant weather conditions.

Additionally, fewer clouds in the region allowed more sunlight to heat the land, potentially exacerbating the drought.

The study concludes that reduced winter sea ice in the Barents and Kara seas can precondition a summer drought corridor across eastern Europe and Eurasia, linking Arctic sea ice loss to drought risk thousands of kilometers away. The findings emphasize the need for action to reduce CO₂ emissions to mitigate the potential impacts of Arctic warming on weather patterns in other regions.