Climate change models over-predict droughts
A study published in the journal Nature this week shows that climate change models may be over-estimating the number of future droughts in a warmer world. This is because the models assume a positive feedback loop between wet soil and more rain. But the researchers found that dry land produces hot convection currents, which in turn can lead to increased rain activity, and found no evidence for the feedback loop:
We find no evidence in our analysis of a positive feedback—that is, a preference for rain over wetter soils—at the spatial scale (50–100 kilometres) studied. In contrast, we find that a positive feedback of soil moisture on simulated precipitation does dominate in six state-of-the-art global weather and climate models—a difference that may contribute to excessive simulated droughts in large-scale models.
Dr Chris Taylor from NERC Centre for Ecology & Hydrology 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.”
The finding is that the feedback mechanism is the exact opposite of those assumed by climate models. The effect this will have on future climate modelling is unclear.