Flood control, irrigation, water supply and hydroelectric power – all require the research of hydrology, the scientific study of earth’s water. Professor Dennis Lettenmaier, in his 2008 Robert E. Horton Lecture on hydrology, traces the history of how hydrologists and meteorologists have helped us to understand the water cycle. As hydrology moves from a qualitative to quantitative science, some are concerned about whether we will be able to answer questions essential to our nation and our world in this era of global change. Lettenmaier uses a projection of the water resources at the Colorado River Basin as a key example of this concern. From the Series:The American Meteorological Society Journal