Extreme rainfall increases as a direct result of global warming

Extreme rainfall events, defined as the heaviest 5% of rain occurrences in a specific area, are increasing globally.

As air temperatures rise, scientists expect such events to intensify because warmer air holds more moisture. Recent years have provided alarming examples, with more extreme rainfall fueling widespread flooding.

What is extreme rainfall?

Extreme rainfall refers to precipitation events significantly heavier than average for a specific region or period. These events, often defined as the heaviest 5% or 10% of recorded rainfall, vary by location and are influenced by unique climatic conditions.

Several meteorological factors drive extreme rainfall. Atmospheric rivers, narrow bands of concentrated moisture, often cause intense downpours.

Tropical cyclones and convective storms – driven by rising warm, moist air – also contribute to heavy rainfall over localized or widespread areas.

Global warming intensifies these events, as the atmosphere can hold approximately 7% more moisture for every 1°C (1.8°F) rise in temperature.

Impact of extreme rainfall

The frequency and severity of extreme rainfall have increased in recent decades, with significant impacts on ecosystems and communities.

Beyond flooding, these events cause soil erosion, reduce agricultural productivity, contaminate water supplies through runoff, and increase the risk of landslides in vulnerable regions.

Notable instances include Hurricane Harvey in 2017, which brought record rainfall to Texas, and the 2018 Kerala floods in India.

Predicting and mitigating the effects of extreme rainfall require advanced climate models, early warning systems, and sustainable infrastructure.

Measures such as improved urban drainage systems and adaptive urban planning can help reduce damage and protect communities from the growing risks of extreme rainfall.

Unexpected pattern in extreme rainfall

When scientists studied the relationship between heavy rainfall and local temperatures in different regions, they discovered an unexpected trend.

In tropical and mid-latitude areas, they observed that extreme rainfall events became less intense when the mean daily temperature exceeded 23°C–25°C (73.4°F–77°F).

This finding was surprising because the prevailing theory suggests that global warming should lead to more intense rainfall events due to increased evaporation and atmospheric moisture.

Instead of aligning with this theory, the data showed a decline in rainfall intensity at higher temperatures, raising questions about the factors influencing these regional patterns. This result highlights the complex and region-specific nature of climate dynamics.

Cooling effect of clouds

Researchers from the Max Planck Institute for Biogeochemistry identified clouds as the key reason behind this puzzling discrepancy.

Rain forms from clouds, which not only produce precipitation but also block sunlight, cooling the ground beneath them.

This cooling effect alters the recorded air temperature, creating a bias in the observed link between rainfall intensity and temperature.

The phenomenon is especially noticeable in tropical regions, where clouds reflect large amounts of sunlight back into space. This reflection amplifies the cooling effect, further complicating the interpretation of temperature and rainfall data in these areas.

Factors behind extreme rainfall

In a study published in Nature Communications, the researchers devised a method to remove the cooling effect of clouds from mean air temperature data.

The experts utilized satellite-derived radiation datasets to refine their analysis. Once they corrected for the cloud-induced bias, the relationship between extreme rainfall rates and rising temperatures aligned closely with theoretical predictions and climate model projections.

“This confirms what is widely expected: Extreme rainfall intensifies in a globally warmer climate,” noted Dr. Sarosh Alam Ghausi, lead author and PostDoc at the Max Planck Institute.

“While heavy rainfall increases mostly everywhere, we found the largest increases in high temperature-driven heavy rainfall events in tropical humid areas such as in India, Northern Australia, and the Amazon.”

Growing threat of flooding

As temperatures continue to rise due to climate change, extreme rainfall events are likely to become even more intense.

Without proactive measures, the risk of devastating floods increases significantly. The findings highlight the need for adaptive strategies to address these heightened risks.

“These results support the physical expectations that the whole hydrological cycle becomes more intense and extreme with warmer temperatures,” noted Dr. Axel Kleidon, senior author and group leader at the Max Planck Institute.

“We will not only see more extreme rainfall rates, but also more intense and longer dry spells in the future.”

Impact of warming on extreme rainfall

This study resolves a key uncertainty in understanding how extreme rainfall responds to warming temperatures.

By accounting for and removing the biases caused by cloud-induced cooling, the researchers confirmed that extreme rainfall patterns align with established climate predictions.

The results highlight a crucial reality: as global warming intensifies, the hydrological cycle becomes more extreme. This means heavier rainfall events in some regions, alongside longer and more severe droughts in others.

With climate change progressing rapidly, these findings emphasize the urgent need for societies to adapt and prepare for increasingly volatile and extreme weather conditions.

The study is published in the journal Nature Communications.

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