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Like tropical cyclones Ida hurricane it can cause severe flooding, causing disruptions, damage and loss of life. Like many other types of weather, tropical cyclones and hurricanes on the U.S. East Coast have been more extreme in recent decades. Although there are some controversy as the intensity increases, such storms are shown to be moving more slowly than in the past. This slower movement lasts longer and produces more storms more rain. However, since conventional weather records are only available until 1948, it is not clear how rare these slow-moving cyclones are compared to previous weather models.
A final examination answers this question by using tree rings to reconstruct the level of precipitation of hundreds of years of seasonal cyclones. The trees studied, some more than 300 years old, show that extreme rainfall is increasing by 2 to 4 millimeters per decade, resulting in a cumulative increase in rainfall of 128 mm (5 inches) compared to the early 1700s. The largest increases have occurred in the last 60 years, and the last extremes are unmatched by previous events.
In addition to establishing these reconstructed historical records, researchers are working with these data sets to improve forecasts of what this region can expect in the future.
Good for growing, at least for trees
In a previous work, Justin Maxwell and his collaborators found this out long-leaved pines It could act as an indicator of tropical cyclone rainfall on the east coast of the U.S., as measured by the growth bands of trees at the end of the season (June to October). These smaller and more local studies indicated that recent rainfall levels were much higher than anything trees had endured earlier in their lives.
This is an unexpected finding, as tree ring records generally show evidence of extreme weather scattered throughout their history, although the frequency may vary. The findings prompted new research, which examined whether this model continued in a broader field.
“Often, the reconstruction of tree rings shows us that the extreme climate we have recorded with instruments (weather stations) over the last 120 years has gone back in time,” Maxwell told Ars Technica. “Past research has shown that the last extremes were unparalleled in the past; the highest values are mostly from the 1990s, which was a big surprise, which led us to try a wider area to see if this rise was local or present. A larger region.”
Combining existing data sets with two new locations, the researchers included trees from seven sites across North and South Carolina. In North America, this region receives the most rainfall from tropical cyclones, and also has the most complete record of this type of rainfall in the world.
The new data sets included a selection of samples of 13 to 36 old trees from each site (taken in a way that caused minimal damage to the trees), as well as liners. The next step for the researchers was to calibrate their model by comparing tree ring models with well-known precipitation measurements from 1948 to the present.
Reconstructing the past to predict the future
As might be expected, tree rings are more significant than the frequency or extremity of individual seasonal rainstorms. But growth patterns clearly suggested less cyclone-season precipitation in the past centuries.
A year of heavy rain does not necessarily mean that a huge storm has passed. “[It] it could represent the rain of a hurricane, or it could have been multiple hurricanes, “Maxwell wrote.” What we found in this paper is that this area is receiving more rainfall from tropical cyclones throughout the season. ” that it is related to the trend of storms that are.
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