Warming Intensifies Rainfall in North Atlantic Storms
A new study led by Newcastle University using satellite data shows that tropical cyclones and their post-tropical cyclone counterparts are responding quite differently to surface warming. The findings reveal that during the tropical cyclone phase, warmer and more humid conditions are causing storm slowdown and strongly increasing rainfall intensity.
Tropical cyclones are a major driver of very heavy rainfall in warm parts of the world. They can bring huge downpours that not only significantly add to total seasonal rainfall but also increase the risk of flash flooding. In the North Atlantic, these storms are especially important during the peak hurricane season (Aug-Oct), with tropical cyclones producing as much as 30–40% of all rainfall in some regions during that season.
Published in the journal npj Climate and Atmospheric Science, the study shows that storm precipitation is rising rapidly with temperature, with median increases of about 21% per degree increase in local dewpoint temperature, while the area of heavy rainfall expands by roughly 12.5% per degree of warming.
At the same time, the overall size of the cyclone tends to shrink slightly with warming, although this process becomes weaker and can even reverse, causing larger tropical cyclones, when sea surface temperatures are very high, particularly in the Caribbean. In these warmer regions, tropical cyclones often move more slowly and last longer, producing more rainfall in one place, especially near to the center of the storm, causing damaging floods.
In contrast, once storms transition into the post-tropical phase, losing their tropical characteristics as they move across the Atlantic towards Europe, they tend to expand in size but are less strongly affected by temperature changes. Rainfall concentrates to the northeast of the storm center and over a wider area, often because the storm is moving faster and is driven by different (baroclinic) weather systems.
Study lead author, Dr Haider Ali, Senior Research Associate, at Newcastle University’s School of Engineering said: “The findings show that global warming is increasing both the intensity and area of rainfall from tropical cyclones, especially in warm, low-latitude regions. Because some storms may also move more slowly, this could greatly increase the risk of flooding in parts of the North Atlantic. This trend will likely continue with increased warming.”