Wed. Dec 1st, 2021

Like a tropical cyclone Hurricane Ida Severe floods can occur, disrupt, cause damage and loss of life. Like many other types of weather, tropical cyclones and hurricanes along the east coast of the U.S. have taken on more extreme proportions over the past few decades. There are some though Debate On the scale of increasing intensity, there is evidence that such storms are moving more slowly than in the past. Because of this slowness the storms are prolonged and generated More rain. However, since conventional weather records only date back to 1948, it is not clear how unusual these slow cyclones are compared to previous weather patterns.

A Recent research Hundreds of years of seasonal cyclones solve this question by using tree rings to reconstruct rainfall levels. The trees studied, more than 300 years old, show that rainfall levels are increasing by 2 to 4 millimeters per decade, resulting in an increase of 128 mm (5 inches) of rainfall compared to the early 1700s. The last 60 years have seen the greatest increase, and the recent extremes cannot be compared to any previous events.

Beyond establishing these restored historical records, researchers are working with these data sets to improve predictions of what the region might expect in the future.

Good for growth – at least for trees

In a previous work, Justin Maxwell and his colleagues found it Long-leafed pine trees Tropical cyclones on the east coast of the United States can act as an indicator of rainfall, as measured by the growth band in the last season of the tree (June to October). These smaller, more local studies indicate that recent rainfall levels were much higher in trees than in previous experiences in their lifetimes.

This is an unexpected discovery, since tree-ring records usually show evidence of extreme weather throughout their history, although the frequency may vary. The discovery led to new research, which examines whether this pattern extends over a wide area.

“Often, tree ring restructuring shows us that the extreme climate we’ve recorded over the last 120 years through instruments (weather stations) has passed over 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 from the 1990s, which was a big surprise, and it encouraged us to look at a wider region sample whether this increase is local or current larger.”

Combining existing data sets with two new locations, the researchers included trees from a total of seven sites across North and South Carolina. Within North America, the region receives the most rainfall from tropical cyclones and also has the most complete record in the world of such rainfall.

The new data sets include a selection of 13 to 36 old-growth tree specimens per site (taken in such a way as to cause the least damage to the tree), as well as stumps. The researchers’ next step was to calibrate their model by comparing tree ring patterns with known rainfall measurements from 1948 to the present.

Reconstruction of the past to predict the future

As might be expected, tree rings represent more seasonal rainfall than individual storm frequencies or edges. But the types of growth clearly indicate that there is less rainfall during the cyclone season in the century.

A lot of rain in a year does not mean that it has gone through a huge storm. “[It] It could represent precipitation from one hurricane, or it could be multiple hurricanes, ”Maxwell wrote. “What we found in this paper is that the region is getting more tropical cyclonic rains throughout the season.” Although field researchers are still debating the cause, many have suggested that it is related to the tendency of storms to move more slowly in the region.

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