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Tropical cyclones such as Hurricane Ida Will cause severe floods, causing damage, destruction and loss of life. Like many other types of weather, tropical cyclones and hurricanes on the east coast of the United States have become more extreme in the past few decades.Although there are some dispute Within the range of increased intensity, there is evidence that such storms move slower than in the past.This slower movement causes the storm to last longer and produce More rainHowever, since traditional weather records can only be traced back to 1948, it is not clear how unusual these slow-moving cyclones are compared to earlier weather patterns.
A sort of Recent studies This problem is solved by using tree rings to reconstruct the precipitation levels of seasonal cyclones over hundreds of years. The trees studied (some are over 300 years old) show that extreme precipitation increases by 2 to 4 millimeters per decade, a cumulative increase of 128 millimeters (5 inches) in rainfall compared to the early 1700s. The greatest increase has occurred in the past 60 years, and the most recent extreme events are unmatched by any previous event.
In addition to establishing these reconstructed historical records, researchers are using these data sets to improve predictions of what may happen in the future in the region.
Good for growth-at least for trees
In early work, Justin Maxwell and his collaborators discovered that Longleaf Pine Trees on the east coast of the United States can be used as indicators of tropical cyclone precipitation, measured by the growth zone of the trees in the late season (June to October). These smaller, more localized studies show that the recent rainfall is much greater than anything these trees experienced earlier in their lives.
This is an unexpected finding, because tree-ring records usually show evidence of extreme weather scattered throughout its history, although the frequency may vary. This discovery prompted new research that examined whether this model is applicable to a wider range of fields.
“Usually, tree-ring reconstructions show us that the extreme climates we have recorded with our instruments (weather stations) in the past 120 years have been exceeded in time,” Maxwell told Ars Technica. “Our past research has shown that recent extremes have been unparalleled in the past-all the highest values are mostly since the 1990s. This is a big surprise, which encourages us to sample a wider area and see Is this increase local or over a period of time. A larger area.”
The researchers combined the existing data set with two new locations, including trees from a total of seven locations in North Carolina and South Carolina. In North America, this region receives the most rainfall from tropical cyclones and is also the region with the most complete record of such rainfall in the world.
The new data set includes selected samples from 13 to 36 old trees at each site (obtained in a way that causes minimal damage to the trees) and tree stumps. The researchers’ next step is to calibrate their model by comparing the tree ring pattern with known rainfall measurements from 1948 to the present.
Reconstruct the past to predict the future
As expected, tree rings are more representative of seasonal rainfall than the frequency or extremes of individual storms. But the growth pattern clearly shows that the precipitation in the hurricane season has decreased over the past few centuries.
A year with a lot of rain does not necessarily mean that a huge storm has passed. “[It] It may represent rain from a hurricane, or it may be multiple hurricanes,” Maxwell wrote. “We found in this paper that the area receives more tropical cyclone precipitation throughout the season. “Although researchers in this field are still arguing about the cause, many people believe that it is related to the slower movement of storms in the area.
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