|Improving the Forecast Models|
|In order to construct
accurate computer models of the boreal ecosystem, the BOREAS team must
take many variables into account. One problem the scientists face is
predicting soil temperatures and knowing when the soils thaw. Soil
dynamics are not easy to track from year-to-year because there are thick
layers of moss that insulate much of forest floor. Current models
dont accurately represent the role moss plays in the hydrological
(water) cycle in the boreal ecosystem.
Moss helps keep the deeper layers of soil frozen, as well as the roots of trees, well into the spring, thereby reducing water vapor. When it rains in the summer, the moss acts like a sponge and soaks up a lot of the water. About one-third of the total amount of water that is evaporated by the boreal ecosystem in the summer comes from moss within a few days after a rain.
|BOREAS measurements show that in the spring and summer, only about
one-third of the solar radiation absorbed by the boreal ecosystem is
used in evaporation, while about two-thirds is emitted as heat. But the
ECMWF model computed that half of the radiation is used in evaporation
and half is emitted as heat. The NCEP model computed that 70 percent of
the solar radiation is used in evaporation and only 30 percent is
emitted as heat. Consequently, these models were predicting more
precipitationas much as 50 percent morethan was actually
being measured (Betts et al. 1998).
By introducing their new BOREAS data into the weather models, Betts
says he expects to see significant improvements in forecasts of daily
temperature, cloud cover and precipitation amounts. It typically takes
a few years to develop and test these forecast model changes, Betts
explains. When the changes that are being tested this summer are
complete, he plans to go back and re-analyze both the old forecasts, the
new forecasts, and the actual measurements to get a quantitative measure
of how much the models have improved. He wont get the results of
those analyses until the year 2000, but loftier goals await over the
"Today, global forecast models are evolving into Earth system models," Betts states. "New land measurements are improving land surface meteorological forecasts significantly, so that there will be another round of improvements to the models in 2001. Then, we will enter our revised understanding of the global carbon cycle into the Earth system models. Over the next 5-10 years, global forecast models will become fairly complete Earth system models."