An international team of top boffins say that current climate models are based on faulty assumptions which lead them to predict more drought than will actually be the case.
At the moment, climate modelling assumes that areas of land that are wet give off more evaporated water, which means that air above such areas will tend to give up any water it is carrying in the form of rain. By contrast air will tend to pass over dry regions without giving up any raindrops, and thus dry places will get drier.
“It’s tempting to assume that moist soils lead to higher evaporation, which in turn stimulates more precipitation,” says Wouter Dorigo of the Vienna University of Technology, one of the authors of the study. “This would imply that there is a positive feedback loop: moist soils lead to even more rain, whereas dry regions tend to remain dry.”
Current climate models are in fact based on this tempting assumption. There’s just one problem with it, according to Dorigo and his colleagues: it’s quite wrong.
“Both heat and moisture are critical ingredients for rain clouds to build up during the afternoon,” explains Dr Chris Taylor from the British government’s Centre for Ecology & Hydrology (CEH), who also worked on the study. “On sunny days the land heats the air, creating thermals which reach several kilometres up into the atmosphere. If the soil is dry, the thermals are stronger, and our new research shows that this makes rain more likely.”