Earth Science

Water Water Everywhere?

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Science  08 Jul 2005:
Vol. 309, Issue 5732, pp. 222
DOI: 10.1126/science.309.5732.222a

Seasonally, the amount of water stored on and in the upper part of the various land areas and river basins varies greatly. These changes are enough to produce subtle differences in the distribution of mass over Earth, which produce slight effects in its local gravity. To detect these slight variations, the satellite mission GRACE flies twin satellites in formation, which communicate with each other, increasing sensitivity greatly. It has been recording global gravity since its launch in March 2002, producing essentially monthly data sets.

Ramillien et al.present an analysis of Earth's terrestrial hydrosphere using the GRACE data for the past 2 years, and attempt to separate out water in snow, groundwater, surface water, and soil water. By inversion, and with precipitation data, this also provides information on net evapotranspiration, an important climate parameter. Although the data resolution is still undergoing improvement, large-scale monthly hydrologic changes are evident over Earth's major river basins, and evapotranspiration seems to be more seasonal in tropical basins than in purely equatorial ones. — BH

Earth Planet. Sci. Lett. 235, 283 (2005).

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