Global warming impact on the number of extreme rainfall events

Researchers from the Massachusetts Institute of Technology and the Swiss Federal Institute of Technology recently published a study that focused on the impact of global warming on the number of extreme rainfall events.

<img src="https://vortex.accuweather.com/adc2004/pub/includes/columns/climatewx/2017/590x364_05181345_schina-flood-20100510.jpg"/>

Excerpts from the <a href="http://news.mit.edu/2017/varied-increases-extreme-rainfall-global-warming-0515">MIT News story...</a>

<em>Since the 1990s, scientists have predicted based on climate models that the intensity of extreme rain events around the world should increase with rising global temperatures. Current observations have so far verified this trend on a broad, global scale. But knowing how extreme storms will change on a more specific, regional scale has been a trickier picture to resolve, as climate data is not equally available in all countries, or even continents, and the signal of climate change is masked by weather noise to a greater extent on the regional scale.</em>

According to the new report, the most extreme rainfall events in a majority of regions across the globe will increase in intensity by 3 to 15 percent, depending on region, for every degree Celsius the Earth's average temperature warms.

For example, much of North America and Europe would experience increases in the intensity of extreme rainfall by about 25 percent if the global average temperature rises by 4 degrees Celsius over the next 100 years, which is what many climate models are predicting based on a relatively high release of greenhouse gases worldwide.

However, there are also a few regions of the world, such as those located over subtropical oceans just outside the tropical equatorial belt, that are projected to see a decrease in these extreme rainfall events.

<em>“The subtropics are generally dry, and if you move the region of descending air poleward, you would get some regions with increases, and others with decreases [in extreme rainfall],” said Paul O’Gorman, a co-author on the paper and associate professor of atmospheric science in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “However, we found that this only explained half of the decreases from changes in winds, so it’s still something of a mystery as to why you get a decrease in precipitation extremes there.”</em>

<strong>How may all this happen?</strong>

<em>As a region warms due to human-induced emissions of carbon dioxide, winds loft that warm, moisture-laden air up through the atmosphere, where it condenses and rains back down to the surface. But changes in strength of the local winds also influence the intensity of a region’s most extreme rainstorms.</em>

<em>“The observations are telling us there will be increases [in extreme rainfall] at almost all latitudes, but if you want to know what’s going to happen at the scale of a continent or smaller, it’s a much more difficult question,” O’Gorman says.</em>

<em>“There is interest around the world in the question of whether to adjust codes to adapt to a changing climate and precipitation, particularly for flooding," said O'Gorman.</em>

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