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Residents living in coastal areas have consistently taken hurricanes very seriously. After all, historical instances demonstrate the significant harm that can result from a hurricane’s fury. What remains less understood is how what was previously termed a one-in-a-thousand-year storm produces wind exposure, tornadoes, record-breaking rainfall, storm surges, and wind-driven waves — and how we will likely observe more occurrences of these storms than ever before, both along the coastlines and inland.
Anyone doubting the importance of enhanced education and facts concerning the hazards posed by extreme storms need look no further than Hurricane Helene, which was one of two one-in-a-thousand-year storms to strike North Carolina last month. A combination of an unnamed tropical storm and Helene, occurring within a two-week span, delivered one-in-a-thousand-year rainfall each time, battering the state. If you have endured one of these storms, our thoughts are with you.
Rainfall as intense as Helene’s now happens approximately once every 70 years due to global warming. Estimating the probability of rare events necessitates increasingly large amounts of data. NOAA’s Atlas 14 was last updated for the Carolinas in 2006, utilizing only data up to the year 2000. Russ Schumacher, state climatologist at Colorado State University, sheds light on the connection between severe storms and climate change.
“Statistics presume that the climate isn’t altering, but we know that it is. Particularly in coastal regions, the incidence of heavy rainfall has grown due to human-induced climate change. Warmer air can retain more moisture, and warmer oceans supply that moisture as fuel for heavy rainfall.”
A one-in-a-thousand-year storm like Hurricane Helene in one location does not imply it will take another thousand years for a similar event to occur again. Instead, for example, in the scenario of a thousand-year rainfall event, the term actually refers to a one in a thousand chance or a 0.1% chance that a specific amount of rain could fall within a given duration. It serves as a gauge of the statistical likelihood of a certain volume of rain falling within a particular timeframe.
The frequency of intense rainfall has risen by 10% over the last 50 years, leading to more frequent and severe flooding globally. What was once regarded as a once-in-a-thousand-year disaster is now a recurring reality, one that is likely to persist. The immediate consequences of such storms today include power outages, flooding both coastal and inland, beach erosion, damage to infrastructure and structures, and direct loss of human life. Significantly, these intense precipitation events are quickly becoming accepted as a part of life, and with that acceptance comes the understanding that what had previously been termed one-in-a-thousand-year storms are misclassified. Their rise in intensity and frequency within an ever-changing climate places stress on daily life.
However, don’t be tempted into thinking that you are completely safe: these estimates merely indicate the probabilities of another one-in-a-thousand-year occurrence. The intensity and frequency of extreme precipitation events in the early twenty-first century have already been observed to be increasing at a pace more rapid than previously anticipated. In the past decade, evidence supporting the rise of short-duration rainfall extremes in a warming climate has accumulated.
In any given year, there’s a 1% probability of a storm arriving that deposits that amount of rainfall in your vicinity, Mari Tye, a civil engineer focused on resilience at the National Center for Atmospheric Research in Boulder, Colorado, informed Bloomberg. The probability also rises the longer you remain in a specific location. So if you were curious about the chances of experiencing a hundred-year rainfall at some point, Tye noted, “you would have a probability more akin to 1-in-4 over the duration of your mortgage.”
Experts assert that the increase in storm intensity since the 1980s can be attributed to significant fluctuations in atmospheric circulation along with rising sea surface temperatures.
Rainstorms are not randomly scattered; they result from atmospheric processes such as thunderstorms and hurricanes, driven by local and regional climate patterns. With a substantial portion of the geographical area in the US population likely susceptible to this new norm of extreme precipitation, it’s time to redefine what it means to experience the current understanding of a one-in-a-thousand-year storm. Now, more than ever, it’s imperative to comprehend changes related to hurricane processes to better inform and prepare coastal communities.
How much of the population is impacted by the underestimation of this risk across the contiguous US? Are existing hydraulic and adaptation structures still adequate to cope with heightened hourly extreme precipitation levels? How well do communities grasp new extreme weather patterns and the likelihood of short-duration heavy precipitation?
The alteration in extreme precipitation comparisons against current national standards for precipitation climatology has come under recent scrutiny. Quantifying the developing frequency of short-duration rainfall extremes poses a challenge for climate change assessments, as the effects of climate change are not typically incorporated into current estimates. Some researchers advocate for revising NOAA’s Precipitation Frequency results as an essential step for addressing flood threats. NOAA researchers are undertaking the challenging task of updating these precipitation frequency estimates based on a shifting climate. They aim to release a new version sometime in 2027. Climate-adjusted national standards are necessary to account for these recent increases that could be employed to avert loss of life and property from catastrophic flood events driven by precipitation.
Sudden, intense, and unforeseen storms like these are no longer uncommon, states the ocean advocacy organization Save the Sound. Instead, “they are becoming the new normal due to climate change.” The group recognizes that “flooding is complex in both causes and effects,” but they urge for urgency in creating a resilient infrastructure plan that includes bridges, culverts, and road stream crossings with flooding considerations. “We should be increasing the use of green infrastructure and safeguarding our region’s forests and marshes, which naturally slow and filter floodwaters,” they assert.
Engineers utilize estimates of the likelihood of rare events to construct large critical facilities, such as dams, capable of withstanding floods resulting from the worst-case scenario rainfall at their sites. It is time to reevaluate current precipitation standards for designing transportation infrastructure and urban stormwater drainage systems as well, in order to protect the public, property, and municipal infrastructure from the impacts of extreme storms.
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