Compound Events Contributing To More Extreme Weather

In recent weeks, there has been a noticeable increase in the frequency and intensity of extreme weather events. These events include hurricanes, heat waves, and wildfires. They are part of a concerning trend where multiple weather events occur simultaneously, intensifying their collective impact. These compound weather events are becoming a significant factor in the surge of extreme weather occurrences, posing challenges for communities and businesses across the United States.

Understanding Compound Weather Events

Compound weather events are a combination of different weather and climate factors that together create potentially high-impact events. For instance, when a heatwave is followed by heavy rainfall, flooding may occur. Similarly, a prolonged drought followed by an intense storm surge can have disastrous consequences. These combined events interact in ways that greatly amplify their impact, resulting in cascading consequences that go beyond the simple sum of their parts. The ARC Centre of Excellence for Climate Extremes aptly compares compound events to going to a doctor’s visit.

While subsequent impacts from weather events are not new, the changing climate landscape is causing events that were once considered unlikely to occur more frequently. Another factor contributing to this phenomenon is that compound weather events often trigger feedback loops, where one event worsens the conditions for another. For example, a wildfire can reduce vegetation cover, increasing the risk of soil erosion and mudslides during heavy rainfall. This creates a domino effect, magnifying the overall impact on communities, businesses, and the environment.

Compound Weather Event Examples

A recent example of a compound event driven by climate change is the catastrophic wildfire event in Hawaii. Studies have shown that climate change is lengthening the wildfire season and increasing the frequency of wildfires. The necessary ingredients for high fire risk—drought, ignitable grass species, and high temperatures—were already present in Hawaii, leading to a red flag warning. The strong winds produced by Hurricane Dora, a Category 4 hurricane, exacerbated the fire. While both events individually can cause structural damage and disrupt business continuity, the occurrence of both extreme events simultaneously amplified the impact.

Wildfires also have compounded health impacts. This summer, wildfires have caused significant air quality issues throughout much of the United States, posing heightened risks to public health. New York City, for instance, experienced its worst-ever wildfire-related air quality, with residents exposed to pollution levels more than five times above the national standard. Earlier this summer, several US cities also faced extremely unhealthy air quality due to wildfires.

Another example of compound weather events can be seen in our oceans. Rising sea surface temperatures can intensify hurricanes, leading to stronger storms and heavier rainfall. Hurricane Ian last year and Hurricane Idalia, the strongest storm to hit the Big Bend area of Florida in over 100 years, are prime examples. Hurricane Idalia reached Category 4 intensity due to warmer sea temperatures in the Gulf, which provided additional energy for its formation. The compounding events with hurricanes include extreme storm surges and rainfall, resulting in devastating flooding even in towns located hundreds of miles from where the hurricane made landfall.

While compound weather events are expected to increase and have unprecedented impacts, it’s important to note that scientists and researchers worldwide are collaborating to prioritize research and technology development. This will help communities and businesses make informed, long-term decisions regarding their finances and infrastructure. Over time, attribution science will be able to scientifically determine to what extent climate change contributed to extreme events. This will further inform governments, businesses, and communities on how to design more resilient plans for a changing climate.