New Study Shows That We’ve Underestimated Extreme Rainfall Events

The climate models scientists have been using for so long may be underestimating how extreme and intense rainfall and future floods will become in response to an increase in greenhouse gases.

Earlier this month, researchers at Yale University sought to better understand the events of extreme and heavy rainfall in the coming years. They found that we cannot determine the magnitude and frequency of extreme rainfall events just by measuring and tracking rain. Even the climate models that researchers use have a part to play in how we predict heavy rainfall.

Long ago, climate researchers discovered that a hotter atmosphere could hold more water vapor. Therefore, global warming increases rainfall. Let’s now forward time to when Hurricane Ida struck the northeastern US. The storm brought amounts of rain that experts predicted would occur only later this century. The Yale study investigated why record-breaking rainfall events like Hurricane Ida were happening ahead of schedule. What makes it rain where it rains? And why is rainfall so extreme in certain places? Lucky for us, we’re in the 21^st century. We have the technology that can help us predict what’s in store for us in the future.

A climate model is a system containing mathematical equations that quantify Earth’s processes. Scientists use many kinds of climate models for various studies. Climate models can be of a regional or a global scale.

The Yale Study

The Yale study used climate models to predict how many events of extreme rainfall would occur in the future. Previous studies of this kind averaged all the available climate models to determine how much rain the Earth would receive in the coming decades. However, the Yale study used only a selected group of models. They selected only the models that predict an increase in natural phenomena like rainfall. They excluded models that forecasted a decrease because reports over the past two decades have shown that climate change is increasing rainfall. For half a century, scientists have been trying hard to determine whether the rain a cloud produces over its lifetime will increase or decrease in a warming climate. The Yale study has shown that the answer to this question lies in how we predict global climate change.

The Yale researchers filtered and used the climate models that most accurately and realistically simulated the physics of raindrops. By doing this, they found that the average climate model today underestimates how extreme rainfall changes in response to global warming.

For the study, the researchers measured precipitation efficiency (PE). PE tells us how much rain gets re-evaporated as it falls from a cloud toward the ground. A PE of 0 means no rainfall. A PE of 1 means all the water from the cloud falls on the Earth. The Yale study focused on how long a cloud would take to give out all its water. They found that climate models with higher resolution information about clouds have a higher PE. A higher PE implies greater precipitation. That means that there could be twice as much rainfall occurring in the 21^st century than previous studies estimated. This would explain why unprecedented rainstorms happening across the globe are shocking scientists. The Yale researchers showed how even a slight change in the percentage of raindrops reaching the ground is the difference between a drizzle and floods.

Response From the Scientific Community

Climate researchers have said that the Yale study is interesting and valuable. The Yale study has shown how scientists can make minor tweaks in their models to get better, accurate, and realistic results. Scientists say that, because of this, we’re getting closer to understanding how climate change is influencing rainfall.

In April 2022, a climate researcher from the University of California, Chad Thackeray, published a study about the frequency of extreme rainfall events as climate change accelerates. Chad also had to filter out and select climate models that accurately demonstrated how global warming is already influencing rainfall. His study concluded that if greenhouse gas emissions decrease very slightly, the frequency of rains will increase by about 30% by the end of the century.

There is currently a lot of work happening around why different climate models give slightly different answers to the same question. There has been a lot of progress in recent decades. But when we come to the question of intense, rare, and extreme events, climate models show significant uncertainty. But they all give one common answer; that rainfall will get more intense and frequent on a warming planet.

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How Can We Adapt?

Rainstorms have brought a large wave of destruction that exceeded expectations. These storms broke all records for global damages in 2021. Extreme and intense rainfall has cost the United States $65 billion, Europe $43 billion, and China $30 billion. Flooded subway systems, land instability, and crumbled infrastructure, among other things, caused these financial losses.

The good news is that governments have the resources and technology to protect people from floods, starting right now. Governments can fund initiatives to strengthen existing infrastructure, such as drainage systems and rooftops. These need to be improved so that the water has someplace to go rather than just pooling on the ground and above buildings and houses. Though the world is unprepared for extreme flooding events and other climate-related disasters, some countries, especially the ones in the tropics that already receive heavy rainfall, are already planning for resilience. Governments need to allocate funds to strengthen transportation infrastructure against climate change. They can also improve sewer systems, pass loans for resilience projects, etc.

That’s our silver lining; we already have the technology to do this. All we need now is serious, responsible action from our governments.