The Azores anticyclone is expanding, according to an article published in the scientific journal ‘Nature Geoscience’, which is causing a greater drought in this area – summers were already hot and arid but wet winters tended to decrease in recent decades, something that has become more frequent. So are we ‘doomed’ to drought?
The study, led by Caroline Ummenhofer, a researcher at the Woods Hole Oceanographic Institution, in Massachusetts, United States, modeled what happened to the Azores anticyclone in the last 1,200 years: according to the authors, the phenomenon began to cover a growing area two years ago. centuries, when greenhouse gas levels skyrocketed, although it became more pronounced in the 20th century.
Geochemical indicators of precipitation levels in recent centuries link this expansion to the onset of drier winters, which could mean that, throughout the 21st century, the risk of droughts will increase, especially if emissions continue to increase.
The Azores are one of the subtropical anticyclones that form in different parts of the Earth. The area of the Equator receives more solar radiation, and this warm air forms a circuit, known as a Hadley cell, that travels to other latitudes. The Azores anticyclone is a branch of this phenomenon that moves north, in the Atlantic, but there are others in the Pacific, Siberia, or the southern hemisphere.
The research used “reanalysis tools” that, in recent times, have made it possible to establish, among other parameters, what the atmospheric pressure fields were in the past when there were no instruments to measure these phenomena. “We can know what the atmospheric pressure was a thousand years ago, even if there were no weather stations, thanks to powerful computational calculations and that is why we know that today the Azores anticyclone is more expanded than ever in the last 1,200 years, which has caused an anomalous behavior in our climate”, explained José Miguel Viñas, a meteorologist at Meteored.
The latest report by the Intergovernmental Panel on Climate Change (IPCC) has already explained that the Hadley cell is rising in latitude. The fundamental consequence is that the Azores anticyclone covers a larger area and blocks the entry of low pressures into the Iberian Peninsula, not only in the summer but in the rest of the year, which translates into more periods of drought in times when it rained before, as reflected in this new study.
“Sometimes they are not severe droughts in the sense that many months go by without rain, but very long periods of drought that cause difficulties in the water supply”, highlighted the expert.
And how do we know how much it rained hundreds or thousands of years ago? One of the fundamental points of the ‘Nature Geoscience’ article is the estimation of the amount of rain that fell annually on the Iberian Peninsula for 1,200 years. The ‘key’ was in a cave in Portugal, the Buraca Gloriosa, which is part of the Alvados caves – the researchers analyzed the growth of stalagmites. Depending on the rainfall regime, more or less material is deposited and, with current techniques, it is possible to study to which period each layer belongs. “If you cross this information with other data, you can recreate a pressure map with between 500 or 700 years and, in this way, make a comparison with what is happening today, collected by instrumental observations”, pointed out the expert.
Source: With Agencies