If we think of the atmosphere as a sponge, we can imagine that the sponge is very dry in the western US, and almost full over humid regions in the eastern US. The addition of moisture to the atmosphere from the land surface in these humid regions makes the sponge leak (makes rain fall). In the west, the dry sponge soaks up any moisture the land surface can contribute without initiating rainfall: rainfall in the west is only initiated by other mechanisms. Credit: Kirsten Findell, NOAA/GFDL
A team of researchers from Columbia Engineering, Geophysical Fluid Dynamics Laboratory, and Rutgers University has now demonstrated that evaporation from the land surface is able to modify summertime rainfall east of the Mississippi and in the monsoonal region in the southern U.S.