Extreme rainfall events, defined as the heaviest 5% of rainfall occurrences in a given area, are becoming more frequent worldwide.
As global temperatures rise, experts predict these events will grow more intense, as warmer air can hold more moisture.
In recent years, extreme rainfall has contributed to widespread flooding, underscoring the growing risks posed by these weather patterns.
Extreme rainfall refers to precipitation significantly heavier than the average for a specific region or time period.
Typically, these events are defined as the heaviest 5% or 10% of recorded rainfall, with their intensity varying based on regional and climatic conditions.
Several meteorological factors drive extreme rainfall, including atmospheric rivers—narrow bands of concentrated moisture that produce intense downpours.
Tropical cyclones and convective storms, which are driven by rising warm, moist air, also contribute to heavy rainfall, whether locally or across larger areas.
Global warming exacerbates these events, as the atmosphere can hold about 7% more moisture for every 1°C (1.8°F) increase in temperature.
The frequency and intensity of extreme rainfall have surged in recent decades, impacting ecosystems and communities.
Beyond flooding, these events lead to soil erosion, reduced agricultural productivity, contaminated water supplies from runoff, and an increased risk of landslides in vulnerable regions.
Notable examples include Hurricane Harvey in 2017, which brought record rainfall to Texas, and the 2018 Kerala floods in India.
To predict and mitigate the effects of extreme rainfall, scientists rely on advanced climate models, early warning systems, and sustainable infrastructure. Measures such as enhanced urban drainage systems and adaptive city planning can help reduce damage and protect communities from these growing risks.
However, a surprising pattern emerged when scientists studied the relationship between rainfall and local temperatures. In tropical and mid-latitude regions, extreme rainfall events tended to lessen in intensity when the daily mean temperature exceeded 23°C–25°C (73.4°F–77°F).
This contradicted the widely accepted theory that global warming should lead to more intense rainfall due to increased evaporation and moisture in the atmosphere. The unexpected trend raised questions about the factors influencing regional climate patterns.
Researchers from the Max Planck Institute for Biogeochemistry identified clouds as the key factor behind this anomaly. Clouds, which produce rain, also block sunlight, cooling the ground below them.
This cooling effect alters the recorded air temperature, leading to a bias in data linking rainfall intensity to temperature.
This phenomenon is particularly evident in tropical regions, where clouds reflect substantial sunlight back into space, amplifying the cooling effect and complicating the interpretation of temperature and rainfall data.
In a study published in Nature Communications, the researchers developed a method to remove the cloud-induced cooling effect from air temperature data using satellite-derived radiation datasets.
Once they accounted for this bias, the relationship between extreme rainfall and rising temperatures aligned with theoretical predictions and climate models.
“This confirms what is widely expected: Extreme rainfall intensifies in a globally warmer climate,” said Dr. Sarosh Alam Ghausi, the study’s lead author.
The researchers found the largest increases in extreme rainfall in tropical regions, such as India, Northern Australia, and the Amazon. These areas are particularly vulnerable to heavy rainfall events driven by rising temperatures.
As global temperatures continue to climb due to climate change, extreme rainfall events are expected to grow more intense. Without proactive measures, the risk of devastating floods will increase significantly.
“The results support the physical expectations that the hydrological cycle becomes more intense and extreme with warmer temperatures,” said Dr. Axel Kleidon, senior author of the study. “We will not only see more extreme rainfall rates, but also more intense and longer dry spells in the future.”
This study resolves a critical uncertainty in understanding how extreme rainfall responds to warming temperatures. By accounting for cloud-induced cooling, the researchers confirmed that extreme rainfall patterns follow established climate predictions.
The findings emphasize the urgency of adapting to and preparing for more extreme and volatile weather conditions as climate change accelerates.
