Much of my early training was in forest hydrology, and as a visual thinker I've always craved dynamic representations of rainfall and runoff on a watershed scale.
Here you have it. I'll just quote the EVL website:
Rain Table is an interactive museum exhibit developed by the Electronic Visualization Laboratory at the University of Illinois at Chicago, the Department of Geology at the University of Minnesota, and the Science Museum of Minnesota.
Rain Table lets museum goers interact with two-dimensional maps of the Earth on a large high-resolution digital table, select locations of rainfall, and then watch as the rain flows down mountains and across fields, cuts channels through slopes and plains, and floods streams and rivers.
Participants position electronic pucks over areas to indicate the location, or locations, of rainfall, as several people can cooperatively interact with the system at once. The pucks' coordinates are input to a mathematical rain runoff simulation model, previously only available to research scientists, which generates a real-time visualization of the rainfalls, the development of channelized streams of water, and the effect of these streams as they merge with one another and flow into lakes and rivers and oceans.
Rain Table technology consists of a 7-by-3-foot, 24-Megapixel display table, built using six Dell LCD 2560x1600 displays, driven by a cluster of 6 computers. Six infrared cameras, mounted overhead, determine the location of the pucks on the table.
The purpose of the exhibit is to educate the general public about rainfall. It demonstrates how rain in one place can cause flash floods elsewhere, or how the distribution and concentration of pollutants, such as oil refinery wastewater or lawn chemicals, affect water supplies.
Direct any questions to Dmitri Svistula (email@example.com) or firstname.lastname@example.org.
Photo from EVL's Rain Table gallery.
Update: From one of the developers, more info, and a movie.