Justin Sheffield is a research hydrologist at Princeton University, New Jersey, USA. He has a PhD in hydroclimatology from Wageningen University in the Netherlands. Dr. Sheffield has carried out research for the past 20 years in the UK and USA on a wide range of hydrologic problems, including the interaction of hydrology with climate variability and change, the characterization of hydrologic extremes, and the use of computer models and remote sensing data to understand the global water and energy cycles.