Monday, 10 February 2003: 5:00 PM
Evaluations of estimates of freshwater discharge from continents
Several new estimates of annual and monthly mean values of continental
freshwater discharge into the individual and global oceans at 1 degree
resolution are compared. While the best estimate is that calibrated with
actual discharge gauge measurements, estimates based on the atmospheric
moisture budget and the inferred evaporation E minus precipitation P, have
potential through being able to provide time series. Atmospheric reanalyses
from the National Centers for Environmental Prediction/National Center for
Atmospheric Research (NCEP/NCAR) and the European Centre for Medium Range
Weather Forecasts (ECMWF) are used along with a snow melt model and a river
routing model to estimate the continental discharge. The discharge and its
latitudinal distribution implied by the observation-based runoff and the
ECMWF reanalysis-based P-E agree well with the river-based estimates, whereas
the discharge implied by the NCEP/NCAR reanalysis-based P-E has a negative
bias. Tests are made using independent estimates of P and the implied E, as
well as the requirement that P should exceed E over land except where surface
flow allows otherwise, such as Southern California. Results suggest that the
P-E data from reanalyses may be used to study the interannual to decadal
variations in continental discharge.
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