Tropical cyclones like Hurricane Ida can cause severe flooding, producing disruptions, damage, and loss of life. Like many other types of weather, tropical cyclones and hurricanes on the US East Coast have become more extreme over the past several decades. Although there is some controversy over the extent of the increase in intensity, there is evidence that such storms are moving more slowly than in the past. This slower movement causes storms to last longer and produce more rain. However, because conventional weather records only go as far back as 1948, it’s unclear how unusual these slow-moving cyclones are compared to earlier weather patterns.
A recent study addresses this question by using tree rings to reconstruct hundreds of years of seasonal cyclone precipitation levels. The studied trees, some over 300 years old, show that precipitation extremes have been increasing by 2 to 4 mm per decade, resulting in a cumulative increase in rainfall of as much as 128 mm (five inches) compared to the early 1700s. The greatest increases have occurred in the last 60 years, and recent extremes are unmatched by any prior events.
Beyond establishing these reconstructed historical records, researchers are working with these data sets to improve forecasts of what this region might expect in the future.