Researchers at Columbia Engineering and Boston University
have developed the first method to map evaporation globally using weather
stations, which will help scientists evaluate water resource management, assess
recent trends of evaporation throughout the globe, and validate surface
hydrologic models in various conditions.
The study was published in the April 1 online Early Edition
of Proceedings of the National Academy of
First time mapping
"This is the first time we've been able to map
evaporation in a consistent way, using concrete measurements that are available
around the world," says Pierre Gentine, assistant professor of earth and
environmental engineering at Columbia. "This is a big step forward in our
understanding of how the water cycle impacts life on Earth."
The Earth's surface hydrologic cycle comprises
precipitation, runoff, and evaporation fluctuations. Scientists can measure
precipitation across the globe using rain gauges or microwave remote sensing
devices. In places where streamflow measurements are available, they can also
measure the runoff. But measuring evaporation has always been difficult.
"Global measurements of evaporation have been a long-standing and frustrating challenge for the hydrologic community," says
Gentine. "And now, for the first time, we show that simple weather station
measurements of air temperature and humidity can be used across the globe to
obtain the daily evaporation."
Evaporation is a key component of the hydrological cycle: it
tells us how much water leaves the soil and therefore how much should be left
there for a broad range of applications such as agriculture, water resource
management, and weather forecasting.
Gentine, who studies the relationship between hydrology and
atmospheric science and its impact on climate change, collaborated on this
research with Guido D. Salvucci, professor and chair of the Department of Earth
and Environmental Sciences at Boston University and the paper's lead author.
Using data from weather stations, widely available across the globe, they
focused on evaporation and discovered an emergent relationship between
evaporation and relative humidity that gave them the evaporation rates.
Gentine and Salvucci plan to provide daily maps of
evaporation around the world that will enable scientists to evaluate changes in
water table, calculate water requirements for agriculture, and measure more
accurate evaporation fluctuations into the atmosphere.
"Sharing our data with researchers around the world
will help us learn more about the Earth's hydrologic cycle and assess recent
trends such as whether it is accelerating," adds Gentine.
"Acceleration could greatly impact our climate, locally, nationally, and