On the Age of Water in the Terrestrial Water Cycle

IAS Benjamin Meaker Visiting Professor Christopher Duffy (Pennsylvania State University) will examine a few of the ways that people have viewed the hydrologic cycle from the 17th century to present through images from published manuscripts, and the methods and models that shaped their understanding. In each of the conceptual models we can see a practical thread where understanding evolved from simple observations and the various interests and motivations of the authors. In each example important questions were raised concerning: What is the source of rivers? Is rainfall sufficient to explain the flow in rivers, or is there another source of water? How long does it take rainfall to form rivers?

As methods and models improved into the present era the questions have evolved but they have a familiar ring: Can we detect changes in the water cycle? Will climate change affect the flow in rivers and how long will it take? What is the role of ecological disturbance and changing land-cover on the water cycle? How long does it take contaminants in the watershed to reach the river? As we might expect, these questions can only be addressed as we understand: “Where does the water come from?” and “How long does it take to get there?” Finally the paper presents an overview of current research that directly models the age of water and tests the model at an environmental observatory in the USA where natural tracers or isotopes of water in rainfall, soil water water, groundwater and streamflow are measured. The paper concludes by reviewing how and why the “age of water” has been and will be an important physical concept for understanding our terrestrial water cycle.

There will be a wine reception in the Geographical Sciences Common Room after the lecture.