Planet Water: Complexity and Organization in Earth Systems
Rafael L. Bras, '72, MS '74, ScD '75, Edward A Abdun"Nur Professor, Civil and Environmental Engineering;
Description: If he doesn't have the whole world in his hands, Rafael Bras certainly grasps more pieces of the gigantic puzzle than most of us. Often credited with launching the science of hydrology -- the study of water's crucial role in Earth systems -- Bras has developed passions for pretty much the rest of the Earth sciences as well. In this fond, valedictory lecture to MIT (he's recently taken the post of Dean of Engineering at UC Irvine), Bras describes some of the research problems that have long fascinated him.
Bras enjoys wrapping his mind around big things, such as the size of the world's oceans, whose numbers are in the billions of cubic kilometers. What interests Bras even more are the ways huge amounts of water cycle from the atmosphere as rain, into the soil, as runoff to the sea, and back again. He says "a lot of what we depend on is the result of differences between large numbers. It is those differences between very large numbers that makes it so uncertain, variable and so sensitive to our intervention or changes."
The physics behind the various water cycles involves vast and continuous transfers of energy: rain changes soil moisture, which changes the amount of radiation the earth reflects, which affects evaporation, which changes the convection potential energy, which impacts cloudiness, which leads again to rain. It's a "very nonlinear, very interacting cycle," says Bras, which is "elegant and quite pretty." Bras helped lay out the models for these cycles. His studies describe how nature seems to prefer extremes like flood and drought, and how in river basins all over the world, nature favors fractal organization and minimal energy expenditure.
Other observation and modeling projects may have consequences for the future of the planet: A nine"year study of an Amazon region that sampled cloud cover from a satellite every three hours demonstrated that deforested regions produce shallow clouds less likely to produce rain, while deeply forested regions generate deep clouds. He has been captivated for the last 10 years by "the intertwined dance between vegetation, landscape hydrology and radiation," how soil moisture accommodates certain kinds of plants, which then change the properties of soil, which changes the drainage capability of water, which over time alters entire landscapes. Concludes Bras, "This beautiful trip through hydrology has been made exciting by all these things I did not know, which came through the exercise of research, trying things and finding things. It is all a result of chance and necessity; things adjust themselves."
About the Speaker(s): Rafael L. Bras recently became Dean of the School of Engineering at U.C. Irvine, after 32 years on the MIT faculty. He came to MIT as a freshman, and earned his graduate degrees at MIT as well, joining the faculty in 1976. He has served as Chair of the MIT Faculty, and head of the Civil and Environmental Engineering Department.
Bras has worked for many government and private institutions, including the Engineering Directorate, National Science Foundation; and the Board of Atmospheric Sciences and Climate, National Research Council. He served as chairman of the Earth Systems Sciences and Applications Committee of NASA, as well as the NASA Advisory Committee.
Bras is a member of the National Academy of Engineering, and is an elected fellow of the AAAS and AMS, among other organizations. He currently chairs a panel of experts supervising the design of a multibillion dollar project to protect Venice from floods. He has also advanced ideas about the impact of deforestation in the Amazon on regional and continental climates.
Host(s): Office of the President, Office of the President
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