Satellites provide the big picture.

Abstract

INSIGHTS Mountain range formation p. 687 Rethinking vascular therapy for cancer p. 694 ▶ PERSPECTIVES WATER Downloaded from www.sciencemag.org on September 14, 2015 Watching water: From sky or stream? Monitoring and management of freshwater resources has long depended upon on-the-ground measurements. Satellite remote sensing has brought new complementing capabilities. In this final of three debates, Science invited arguments about the appropriate roles for, and balance between, each approach. By J. S. Famiglietti, 1, 2, 3 * A. Cazenave, 4, 5 A. Eicker , 6 J. T. Reager, 1 M. Rodell , 7 I. Velicogna 1 ,2 Satellite observations have revolutionized our understanding of hydrology, water availability, and global change, while catalyzing modern advances in weather, flood, drought, and fire prediction in ways that would not have occurred with relatively sparse POLICY ground-based measurements alone. Earth-observing satellites provide the necessary “big-picture” spatial coverage, as well as the regional-to-global understanding essential for improving predictive models and informing policy-makers, re- source managers, and the general public. Sustained investments in a robust satellite hydrology program have enabled a plethora of discoveries, along with modernization of water management, that have increased the human, economic, and water security of many nations. We now recognize distinct human- and climate-driven fingerprints on the water landscape that are dramatically changing the distribution of freshwater on Earth ( 1). Improved understanding and heightened societal aware- ness of the global extent of sea-level rise ( 2), ice sheet and glacial melt ( 3), changing rainfall patterns ( 4), declining snow cover ( 5), groundwater depletion ( 6), and the changing extremes of flooding ( 7) and drought ( 8) simply would not have occurred without satel- lite observations. As we look ahead, ongoing and near-future missions will soon provide routine global monitoring of the stocks of soil moisture ( 9), surface water ( 10), and total water storage ( 11)—which will im- prove estimates of groundwater storage changes ( 12)—and of the fluxes of precipitation ( 4) and evapotranspiration ( 13). Taken to- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. Department of Earth System Science, University of California, Irvine, CA, USA. 3 Department of Civil and Environmental Engineering, University of California, Irvine, CA, USA. 4 Centre National d’Etudes Spatiales–Laboratoire d’Etudes Geophysique et Oceanographique Spatiales (CNES/ LEGOS), Toulouse, France. 5 International Space Science Institute, Bern, Switzerland. 6 Institute of Geodesy and Geoinformation, University of Bonn, Germany. 7 NASA Goddard Space Flight Center, Greenbelt, MD, USA. *Corresponding author. E-mail: james.famiglietti@jpl.nasa.gov. sciencemag.org SCIENCE 14 AUGUST 2015 • VOL 349 ISSUE 6249 Published by AAAS ILLUSTRATION: DAVIDE BONAZZI Satellites provide the big picture