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Megadrought impacting western U.S more intensely due to climate change

Megadrought emerging in the western U.S might be worse than any in historical record, new study says. While the megadrought is a naturally occurring event that started in the year 2000, climate change might be responsible for its destructive impact.

A study published in the Science journal demonstrates appearance of megadroughts over the last 1,200 years that occurred in western North America. The methods that researchers used, allowed to show that time frame from 2000 to 2018 was the driest period since the late 1500s and second driest since 800 CE. They relied on information from tree rings, which were used to identify periods that were more severe and prolonged.

Scientists at Oregon State University and Utah State University in their study of mixed-conifer forest in central Oregon, presented what findings can be seen using a tree-ring method. The research was published in Global Change Biology and explains that for example when trees used more of heavier stable isotope of carbon for photosynthesis, it was showing the drought stress increase as the passage of gases into their leaves was restricted. Moreover the higher CO2 concentrations also had an effect on leaf gas exchange, and the research suggests that atmospheric CO2 has increased 40% since the dawn of the industrial age. Method allowed to show that trees respond to drought by becoming more efficient with their water use.

Their ring-size variation can tell us about the temperature when growing occurred and the chemistry of each ring says about whether it uses the preferred carbon-12 isotope or a heavier isotope for photosynthesis.

Hydrological modelling was another method to demonstrate the occurring phenomenon. Impacts of drought can be managed through preparedness planning and understanding of water resources. One of the project examples where hydrological modelling was used is called CreativeDrought and the area selected in the study was the Limpopo Basin in South Africa.

The study involved field visits, where the information was collected about land use and water users; the community was involved in the discussions about their past experiences of drought and divided into groups depending on different types of resource users.

Those field visits allowed to notice lack of engagement or preparation for future drought. Scenarios used on hydrological modelling helped participants explore those hypothetical future situations that can occur in different ways.

They have engaged with creating their own future droughts narratives and discuss with others their preparation and adaptation.

Those both methods combined- hydrological modelling and tree-ring- allowed researchers to show period from 2000 to 2018 as the driest since 1500s. According to Thursday’s Journal Science, half of the historic drought can be blamed on man-made global warming.

Climate change is not the cause of the drought, but the hotter air holds more moisture and dries out soils, making more impact and damage during droughts. The article in Independent  by Harry Cockburn from 17 April 2020 says:

“Since temperatures are projected to keep rising, and with the world currently on course to see 3-4C higher temperatures by the end of the century unless dramatic action is taken to limit fossil fuel emissions, it is likely the drought will continue for the foreseeable future or fade briefly only to return.”

There is evidence that the drought is contending in severity and climate change did contribute in some part to make its impact worse. According to Smithsonian magazine, that as with past megadroughts, the current event is driven largely by natural variations in climate. Although comparing to prehistoric megadroughts, the fact that the event is happening in era of climate change is responsible for nearly half of its destructive impact, they say.

By: Julita Waleskiewicz

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