Study shows why rainfall remains hard to predict in a warming world
A study led by the University of Oxford and ETH Zurich reveals that a key part of the climate system - the large-scale wind patterns that determine where rain falls – can be underestimated by current climate models, helping explain why forecasts of regional rainfall remain uncertain. Ultimately, this insight could enable more confident projections of future rainfall patterns, supporting better preparation for floods and droughts. The study has been published today in Nature .
The findings are based on an analysis of winter rainfall patterns across the Northern Hemisphere from 1950 to 2022. This revealed that while scientists can reliably predict how a warmer atmosphere holds more moisture, they are far less certain about how circulation patterns will shift in response to human emissions - and these are what ultimately determine where rain falls.
Rainfall affects everything from food production and water supplies to flooding and energy systems. As climate change accelerates, many regions are already experiencing more erratic weather - longer droughts punctuated by more intense rainfall.
But preparing for these changes depends on knowing where they will happen. Recent extreme rainfall events, including the widespread floods across Europe in 2024, have shown how difficult it remains to anticipate exactly where and how severe heavy rain will hit.
Two forces shaping rainfall
The researchers examined two key processes that drive changes in rainfall:
- Thermodynamic effects: heat- and moisture- related effects, for instance the fact that a warmer atmosphere can hold more moisture, increasing the intensity of rainfall when it occurs.
- Dynamic effects: shifts in large-scale circulation patterns, such as the jet stream, which control storm tracks and rainfall distribution.
Using a combination of statistical methods and advanced climate model experiments, the team separated these influences. This revealed that climate models consistently capture thermodynamic changes. However, they struggle to represent changes in large-scale circulation patterns, particularly in regions where these patterns play a dominant role.
In Southern Europe, for example, current climate models simulate only around 10% of the observed circulation-driven rainfall trend, highlighting a major gap in current projections.
Why rainfall is so hard to predict
The study identifies two main reasons for this uncertainty.
First, atmospheric circulation naturally varies over decades. Large-scale patterns such as the North Atlantic Oscillation can shift unpredictably, masking or amplifying long-term climate trends.
Second, climate models may underestimate how these circulation patterns respond to human-driven climate change. This makes it difficult to distinguish between natural variability and long-term change - and limits confidence in regional forecasts. As a result, it is challenging to tell whether rainfall changes are caused by temporary, natural swings or part of a long-term shift driven by human-induced climate change. This reduces confidence in predictions of where rain will increase or decrease.
Together, these factors mean that even when overall global trends are clear, predicting local rainfall changes remains challenging – especially in regions already vulnerable to drought or flooding.
“By combining two complementary approaches, we were able to show that climate change is already influencing the large-scale wind patterns that shape rainfall, even though the size of that effect remains uncertain. Our work aims to better understand how we can make model simulations of rainfall more robust.” - Dr Lei Gu, Lead author, Department of Physics, University of Oxford