Researchers have published new findings that suggest European drought trends are lining up with climate change projections.
Their study, in Scientific Reports, shows that two major drought indices are deviating from one another across Europe in a manner consistent with climate change simulations.
“This is one more big drop in the bucket toward climate change attribution,” said lead author James Stagge, a post-doc at Utah State University’s Utah Water Research Lab. “There have been a lot of projections, but now that we’re starting to see the projections and observations line up, it’s not a question of ‘is it happening?’ It’s a question of ‘how much?’ And ‘what do we do?’”
The spatial patterns observed by Stagge and his team match climate change projections for Europe that suggest decreases in drought frequency in the north and increases of drought frequency in the south. “Once you add in the temperature increases for all of Europe”, said Stagge, “you have all the hallmarks of our climate change projections.”
As temperatures increase across Europe it increases evapotranspiration, or what is leaving the ground and going back into the atmosphere. One drought index captures this, while the other does not. When evapotranspiration is included, the border from where it is getting wetter to where it’s getting drier is pushing farther and farther north.
David Hannah, Professor of Hydrology at the University of Birmingham, explained, “So it’s not just the Mediterranean that’s getting drier. It’s pushing up into Germany and England. It’s moving everything farther north.”
This increasing deviation in European drought frequency is observed from the 1980s until today. In a stationary climate, the researchers say they would expect this difference to be randomly distributed and stable like it was from the 1950s through the 1970s.
“This recent and consistently increasing trend is a clear signal, not random noise,” he added.
The new findings are important to the scientific community and could influence public policy and Europe’s agriculture industries. Many drought monitoring agencies use the indices to determine what constitutes drought, and insurance pilot programs have considered using them to determine whether or not farmers are entitled to compensation.
“The research highlights the increasing need to carefully define drought in a changing climate,” said Stagge. “Indices that were standardized in the past may drift significantly in a changing climate depending on how a data set is measured and what time period is considered.”
The study was verified using two sets of data, primarily WFD/WFDEI, and E-OBS as an external check. Additionally, the team, which includes Lena Tallaksen (University of Oslo, Norway), Daniel Kingston (Otago University, New Zealand), and David Hannah (University of Birmingham, UK), used several alternative evapotranspiration models to validate their findings.
The study was funded by the European Union’s DROUGHT-R&SPI project and is a contribution to the UNESCO-IHP FRIEND-Water program.
More information: James H. Stagge et al, Observed drought indices show increasing divergence across Europe, Scientific Reports (2017).
James Stagge – Utah Water Research Lab, Utah State University |(203) 939-2323
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