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July 10th, 2022
Via The Guardian, an article on the drought affecting Spain and Portugal:
Spain and Portugal are suffering their driest climate for at least 1,200 years, according to research, with severe implications for both food production and tourism.
Most rain on the Iberian peninsula falls in winter as wet, low-pressure systems blow in from the Atlantic. But a high-pressure system off the coast, called the Azores high, can block the wet weather fronts.
The researchers found that winters featuring “extremely large” Azores highs have increased dramatically from one winter in 10 before 1850 to one in four since 1980. These extremes also push the wet weather northwards, making downpours in the northern UK and Scandinavia more likely.
The scientists said the more frequent large Azores highs could only have been caused by the climate crisis, caused by humanity’s carbon emissions.
“The number of extremely large Azores highs in the last 100 years is really unprecedented when you look at the previous 1,000 years,” said Dr Caroline Ummenhofer, at Woods Hole Oceanographic Institution in the US, and part of the research team.
“That has big implications because an extremely large Azores high means relatively dry conditions for the Iberian peninsula and the Mediterranean,” she said. “We could also conclusively link this increase to anthropogenic emissions.”
The Iberian peninsula has been hit by increasing heatwaves and droughts in recent years and this year May was the hottest on record in Spain. Forest fires that killed dozens of people in the region in 2017 followed a heatwave made 10 times more likely by the climate crisis, while the Tagus River, the longest in the region, is at risk of drying up completely, according to environmentalists.
The new research, published in the journal Nature Geoscience, analysed weather data stretching back to 1850 and computer models replicating the climate back to AD850. It found that, before 1850 and the start of significant human greenhouse gas emissions, extremely large Azores highs occurred once every 10 years on average.
From 1850 to 1980, the frequency was once every seven years, but after 1980 this rose to every four years. Data showed that extremely large Azores highs slash average monthly rainfall in winter by about a third. Further data from chemical analysis of stalagmites in caves in Portugal show that low rainfall correlates closely with large Azores highs.
The computer simulations of the climate of the past millennium cover a period up to 2005. But other studies covering later years are consistent with new findings and the Azores high is expected to continue to expand, further increasing drought on the Iberian peninsula, until global carbon emissions are cut to net zero.
“[Our findings] have big implications for the water resources that are available for agriculture and other water intensive industries or for tourism,” said Ummenhofer. “It doesn’t bode well.” Spain was the second most popular country for overseas tourists in 2019, hosting 84 million visitors.
Spain also is the world’s biggest producer of olives and a major source of grapes, oranges, tomatoes and other produce. But rainfall has been declining by 5-10mm a year since 1950, with a further 10-20% drop in winter rains anticipated by the end of the century.
Other research has projected a 30% decline in olive production in southern Spain production by 2100 and a fall in grape-growing regions across the Iberian peninsula of 25% to 99% by 2050 due to severe water shortages. Research in 2021 also linked the Azores high to the summer monsoon in India.