For the Sept. 3rd How On Earth show we offer two features:

Wildfires Threaten Water Supplies: (start time 5:45) The wildfire burning in and around Yosemite National Park is now the fourth-largest in California’s history. Covering nearly 350 square miles, the Rim Fire is threatening the Hetch Hetchy Reservoir, which supplies residents in the San Francisco Bay Area with most of their water and power. It’s a lot like the 2012 High Park Fire—which sent ash and debris into the water supply of Fort Collins. These fires offer lessons on the risks wildfires pose to reservoirs.  Dr. Bruce McGurk, a former water manager for Hetch Hetchy and a water consultant, speaks with How On Earth contributor Brian Calvert about the risks and future prospects.

Comet ISON Cometh: (start time 12:50) Comets have fascinated humans for millenia.  Aristotle argued comets were hot, dry exhalations gathered in the atmosphere and occasionally burst into flame.  Some people thought that comets replenished Earth’s air. Still others  believed they were a source of disease.  Scientists today study comets because some are thought to be relatively pristine leftover debris from the formation of the solar system. And studying what comets are made of can provide us a glimpse back to the beginning of the solar system 4 billion years ago.  Comet ISON, as scientists call it, is one that scientists predict will be relatively easy to view later this year. Dr. Carey Lisse, a senior research scientist at the Johns Hopkins Institute Applied Physics Laboratory in Maryland, speaks with co-host Joel Parker about comet ISON and its fascinating tails. For more information on ISON, go to NASA’s ISON toolkit, and this cool interactive model.

Hosts: Susan Moran, Joel Parker

Listen to the show: