New light has been shone on extreme weather events by a team of engineering and mathematics experts.
The researchers from Columbia Engineering, Geophysical Fluid Dynamics Laboratory, and Rutgers University have tried to explain the relationship between water on the earth's surface and atmospheric conditions.
It had long been thought that moist soils helped cause rainfall, but there was little actual observational evidence of this until this new study.
However, evaporation does not increase the amount of rain according to the team who say that only the frequency of precipitation goes up.
"This is a major shift in our understanding of the coupling between the land surface and the atmosphere, and fundamental for our understanding of the prolongation of hydrological extremes like floods and droughts," said Pierre Gentine, Assistant Professor of Applied Mathematics at The Fu Foundation School for Engineering and Applied Science at Columbia University, and co-author of the paper "Probability of Afternoon Precipitation in eastern United States and Mexico Enhanced by High Evaporation," published in the new edition of Nature Geoscience.
The study is geographically based and used data from the United States National Centres for Environmental Prediction (NCEP).
The results too were geographically distinct with evaporation increasing the likelihood of afternoon rainfall east of the Mississippi and in Mexico but not in the western United States. That's because the humidity in the western US is so low that no amount of evaporated moisture will trigger rainfall. The opposite is true east of the Mississippi.
"If it starts getting really wet in the east," noted Gentine, "then the surface will trigger more rain so it becomes even moister, and this sets up a vicious cycle for floods and droughts. Nature - i.e. the land surface and the vegetation - cannot control the rainfall process in the west but it can in the east and in the south. This is really important in our understanding of the persistence of floods and droughts."
This means that extremes such as flood and drought are much more likely in the east and south of America but in the west little can be done – away from the oceans that are the prime cause of such extremes – to influence weather conditions.
In time Gentine believes his work will have a practical application in dealing with weather extremes.
He said: "I find this work fascinating because it's a great blend of theoretical research - understanding how nature works - and practical applications that affect our world - like flood/drought/water management. My lab is right outside: observing clouds and precipitation!"
Image Credit: © Stas Perov