Formation of the European Union altered climate across the region, according to a recent study. And without the advent of the EU and its accompanying changes in land-use, the 2003 heatwave may have been even more severe.

The European Union came into being on 1 November 1993. Two years earlier, on 25 December 1991, independence was granted to the Union of Soviet Socialist Republics. These two changes had major political and economic ramifications, and completely altered the way that land across the region is managed. Across Eastern Europe, the Iberian Peninsula and Italy, agricultural land was abandoned, with much of it reverting to grassland.

Samuel Zipper from the University of Victoria in Canada and colleagues investigated the impact of this land-use change by simulating water and energy cycles across the region during the period of land-use change – 1990 to 2010. Around 8.5% of land in the region changed use during this time.

This land-use change may have substantially increased cloud cover and decreased incoming shortwave radiation over western Europe, the team found, even in locations where land-use change didn’t occur.

“What we think is happening is that the agricultural abandonment led to an increase in the amount of water that plants transpired into the atmosphere, which caused increased cloud formation,” says Zipper.

Overall, the simulations suggest that the land-use change across Europe decreased peak air temperatures over much of the region, and may have helped lessen the impact of heatwaves, including the devastating heatwave in August 2003 thought to have caused more than 40,000 deaths and 13.1 billion euros in damages.

“Our results suggest that if this land use change had not occurred, the 2003 heatwave may have been more severe,” says Zipper, whose findings are published in Environmental Research Letters (ERL).

The model also shows that climate feedback was reduced in regions with shallow groundwater. “Soil moisture and shallow groundwater supply water to plants, and the more water plants use the cooler temperatures will be,” says Zipper.

The study indicates that land-use decisions made now could have significant impact on future climate, particularly on air temperature and extreme heat. Zipper and colleagues suggest that we consider what kind of land-use changes will help to mitigate, rather than exacerbate, the impacts of climate change. Irrigation, they point out, can help to maintain high soil moisture levels and reduce extreme heat locally. But this mustn’t be done at the expense of depleting local streams and aquifers, they caution.

And the researchers note that the bigger the difference in land-use type, the bigger the impact on climate. “Going from forest to an urban area would have a larger effect than going from forest to a grassland,” says Zipper.