For at least a century, there has been no such thing as these hurricane seasons. Like many other types of weather, tropical storms and hurricanes have intensified off the east coast of the United States over the past few decades. Although there is some dispute about the scale of the increase, there is evidence that such storms are moving more slowly than ever before. This slower movement makes storms last longer and produces more rain. However, since normal weather records only go back to 1948, it is not clear how unusual these slow-moving storms are compared to previous weather patterns.
A recent study uses tree rings to recreate hundreds of years of monsoon rains for this year's storms. The studied trees, which are over 300 years old, show that precipitation increased by 2 to 4 mm per decade, resulting in a cumulative increase in precipitation of up to 128 mm (five inches) compared to the early 18th century. The largest increase has occurred in the past 60 years, and is unparalleled by any previous event in recent extremes.
In addition to creating these reconstructed historical records, researchers are working with this dataset to improve future projections for the region.
for growth—at least for trees
In a previous study, Dr. Justin Maxwell and colleagues found that deciduous pine trees on the east coast of the United States could serve as indicators. Tropical storm rain, as measured by tree growth bands in the late season (June to October). These smaller, more localized studies show that recent rainfall was much higher than anything the trees had experienced in their lifetime.
This is an unexpected finding, as records of tree rings generally show evidence of severe weather prevalent throughout its history, although the frequency may vary. This finding prompted a new study to examine whether this pattern exists in wider areas. "It's been 120 years," Dr. Justin Maxwell said in an interview with Ars Technica. “Our previous research showed that recent extremes have not been seen in the past - all of the higher values are basically all back to the 1990s, which was a big surprise and encouraged us to sample from a wider area to see if this is a local increase in North America, this region receives the most precipitation. of tropical storms and also has the most complete world record for this type of rain.
The new dataset includes a set of samples from 13 to 36 trees growing at each site (taken in a way that causes the least damage to trees), as well as tree trunks Calibrate the tree with known rainfall measurements from 1948 to the present. Seasonal periods are more pronounced than frequency or intensity of individual storms, but growth patterns are clear showing little rainfall over past centuries.
General with heavy rainfall Not necessarily this does not mean that a major storm has passed. “It can show rain from a single storm, or it could be multiple storms,” Maxwell wrote. “What we found in this article is that this area receives more tropical rain throughout the season.” While Researchers are still discussing Shawn's reason, many believe, is related to the trend of slowly moving hurricanes in the area. Worldwide, hurricane translation speeds have decreased by up to 10 percent in the past 70 years due to weakening global wind currents. “This [increase in rainfall] is caused by storms hanging over a longer area than before,” Maxwell said. Study author Dr. Joshua Bergé is working with other experts to see if these reconstructions have been used to help predict storm seasons. we can use .
"Based on our current knowledge of the global climate system, in a warmer world, global winds are weaker." If warming continues, as expected, these global winds will remain weak. Global winds drive tropical cyclones, so weaker winds cause "more storms to wrap and stop storms in one place, producing more rain. Therefore, this great monsoon season of tropical storms is likely to continue into the future."
PNAS, 2021. DOI: 10.1073/pnas.2105636118
KED Kwan is a freelance journalist covering climate and environmental stories at Ars Technica. He holds a PhD in Chemistry and Chemical Biology.
300-year-old tree rings confirm recent increase in rainfall
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