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Thunderstorms are most common in the late afternoon, when plenty of heat has built up, but in years to come a different pattern might emerge. A simulation of future rainfall suggests that climate change could push the heaviest downpours into the night or even the early morning.

As the climate heats up due to our greenhouse gas emissions, heavy rainfall events are becoming more severe. However, it is less clear exactly how and when this extra rain will fall, and thus how it will affect us.

One overlooked issue is when the rain will fall during the day. 鈥淭he scaling of extreme precipitation hasn鈥檛, as far as we鈥檙e aware, been looked at across the diurnal cycle,鈥� says Edmund Meredith of the Free University of Berlin in Germany.

Meredith and his colleagues simulated the climate of Europe at a resolution of 12 kilometres, then focused in on a smaller region of western Europe at a resolution of 2.2 kilometres. This was detailed enough for them to see individual rainstorms, which has not been possible in climate models until recently. They did this for 1970-1999, and then for 2070-2099 assuming lots of greenhouse gases are emitted this century.

In the historical period, the heaviest rainstorms happened in the late afternoon. This is because the sun鈥檚 heat warms the ground, heating the air above it and causing it to rise. This convection current carries lots of water vapour high into the air, where it cools and forms rain clouds.

But in the future climate, compared to the historical period, the biggest increases in rainfall occurred in the morning. 鈥淚n some regions, you might actually be more likely to get the extremes earlier in the day than is currently expected,鈥� says Meredith. This was because the most powerful convection currents, which drive the rainstorms, occurred in the night or early morning.

It鈥檚 unclear whether this would apply to other regions. 鈥淚 wouldn鈥檛 want to extrapolate our results to the rest of the world, but it鈥檚 certainly a plausible course of events for similar regions,鈥� says Meredith. However, he points out that a strong convection current will only cause a rainstorm if it forms in a place with moist air.

suggests that climate change is also causing an increase in the amount of rain that comes from persistent rainfall over multiple days, rather than single-day events.