Clouds obscure the relationship between extreme rainfall and rising temperatures

Extreme rainfall is typically defined as the heaviest 5% of rainfall in a given region. As global temperatures rise, scientists expect extreme rainfall to increase. Because warm air can hold more moisture. Recent examples of more extreme rainfall have been evident in further floods that have occurred around the world in recent years.

But when scientists looked at how heavy rainfall was related to local temperatures across the region, they noticed an unexpected pattern that seemingly contradicted theory. The researchers found that in warm tropical and mid-latitude regions, extreme rainfall rates decrease as average daily temperatures rise above about 23 to 25 degrees Celsius.

A research team led by the Max Planck Institute for Biogeochemistry in Jena, Germany, resolved this discrepancy and found that clouds were the culprit. Rain falls from clouds, which also block sunlight from entering, thereby cooling the earth’s surface. Therefore, average temperature is influenced by clouds. As a result, the true correlation between extreme rainfall and rising temperatures is biased. This is especially true in warm tropical regions where clouds reflect more sunlight.

In a study published in Nature Communications, the authors developed a method to remove the cooling effects of clouds from average temperatures using satellite-derived radiation datasets. After removal, they found that the increase in extreme rainfall rates with temperature matched theoretical expectations and climate model predictions very closely.

“This confirms what is widely expected: warmer climates worldwide intensify rainfall extremes,” said lead author and postdoctoral researcher at the Max Planck Institute for Biogeochemistry in Jena, Germany. says Dr. Sarosh Alam Gausi. He added: “While heavy rainfall is increasing almost everywhere, we find that tropical humid regions such as India, northern Australia and the Amazon have seen the greatest increases in heavy rainfall due to high temperatures.”

Extreme rainfall events are expected to further intensify, potentially increasing the risk of flooding if proactive measures are not taken. And as temperatures rise due to climate change, extreme precipitation is expected to continue to increase.

Dr Axel Claydon, senior author and group leader at the Max Planck Institute, said: “These results confirm the physical expectation that the overall water cycle will become more intense and extreme as temperatures rise. Not only will we observe more extreme rainfall rates, but we will also see more intense and longer dry spells in the future.