'Water runoff' is, basically, rain, snowmelt, and irrigation water that doesn't get absorbed into the soil. If you're on, say, a glacier, runoff can create waterfalls. Runoff causes erosion and is the most important measure of flood prediction. Water flowing at just 60 centimeters (two feet) per second can move half-pound rocks easily, and such speeds occur in forested areas that do not make efforts to reduce erosion.
Han found that, overall, water runoff speed in the Amazon is 30 centimeters per second, and that there's a large difference in speeds depending on the season. This is an elegant result, showing how detailed data on one item-- the mass of a section of the Earth-- can help you understand how a complex water system like the Amazon operates.
That's my simple summary, the sort of thing I write here at ScientificBlogging. Good science blogging has five parts:
- a quick overview of the work
- the method and tools
- a brief definition of terms
- the research's result and conclusion
- a brief "why it matters"
"Gravity-measuring satellites used to observe Amazon surface water storage and its dynamics." (EOS)
Scientists would like to better understand the physical processes in Amazon hydrological systems. To explore the water storage and dynamics in the Amazon basin, Han et al used 4 years of data from the two Gravity Recovery and Climate Experiment (GRACE) satellites, which measure mass distribution on Earth's surface through instantaneous measurements of the changes in distance between the satellites. Water stored in the Amazon basin affects mass distribution and thus can be monitored by the GRACE satellites. The authors found that soil water explained about half of the observed changes in intersatellite distance; surface and subsurface runoff explained the rest. By comparing river runoff routing simulations with GRACE data for the Amazon region, the authors found that the overall effective runoff velocity for the entire Amazon basin was about 30 centimeters per second, with significant seasonal variation. They conclude that incorporating GRACE data can help improve routing schemes in large-scale land surface models.
And then there is the formal research language. This is what is published in scientific journals. It is detailed, it is dense, and it is often complex. Sometimes, too complex-- I had one co-author complain that my paper was written too simply and thus made the results sound obvious. He proceeded to make the language more arcane, to better its chances of publication. One hopes he was the exception, but I would say it is harder to be both precise and clear, than to be one without the other.
Here is Shin-Chan Han and team with their original abstract, from Geophysical Research Letters (GL), Volume 36, Issue 9:
"Dynamics of surface water storage in the Amazon inferred from measurements of inter-satellite distance change" (GL)
Terrestrial water storage in the Amazon basin and its surrounding areas is studied by exploring the instantaneous measurements of distance changes between two satellites from the GRACE mission. The surface water in the channels and floodplains can be significant in weighing total water storage. Its magnitude can be as large as soil moisture perturbing the motions of the satellites to a detectable amount by the on-board instrument. The river runoff routing simulations indicate the effective velocity throughout the Amazon basin over the years is about 30 cm/s with significant seasonal change. The lower velocity, during rising stages and peak water season, and the faster velocity, during falling stages, are delineated from the observations. The backwater effects may impact such seasonal change on the overall flow velocity. Direct assimilation of GRACE tracking data can contribute to land surface dynamic processes by resolving the time scale of transport in rivers and streams.
So there you have it-- a neat result, in three different languages. Which do you prefer?
Alex, the Daytime Astronomer
Tues&Fri here, via RSS feed, and twitter @skyday
Read about my own private space venture in The Satellite Diaries