Dry soil's penchant for causing rain shows where our climate models can go wrong

Illustration for article titled Dry soil's penchant for causing rain shows where our climate models can go wrong

A large, multi-continent study published in this week's Nature has exposed a significant flaw in how climate models have been predicting droughts.


Dr Chris Taylor from NERC Centre for Ecology & Hydrology was studying storm formations in Africa, when he realized that rainfall was most likely in places where the soil was dried out. In a press release, he said:

"We had been looking at storms in Africa and knew that rain clouds there tended to brew up in places where it hadn't rained in the previous few days. We were surprised to see a similar pattern occurring in other regions of the world such as the US and continental Europe. In those less extreme climates, with more vegetation cover, we expected the soil wetness effect would be too weak to identify."

Across all the continents they saw a similar pattern — "afternoon rain falls preferentially over soils that are relatively dry compared to the surrounding area."

What makes this discovery really interesting is that this is the exact opposite of what most of the current climate prediction models suppose. The researchers looked at six global weather and climate models used to simulate climate change, and all of which were based on positive feedback — that wet soils trigger rain. These models can form a feedback loop, where dry areas don't get rainfall, which causes even dryer conditions.

That's not to say that the models of climate change make things seem worse than they are — we don't know yet. It's now a challenge to adjust the models to the new data, and see if the long term impacts change at all from this information.

Top photo by how lucky we are.




So why do long extended droughts happen at all?