Jose A. Marengo CPTEC - Centro de Previsăo do Tempo e Estudos Climáticos (INPE) (SA-PI)
Charles J. Vorosmarty University of New Hampshire (US-PI)
The principal goal of this
research is to establish a water budget closure system (WBC-LBA) for computing
high-resolution water balance elements in support of the LBA Project. The
system will integrate several existing scientific tools including algorithms
that produce high-resolution climatology fields, water balance and river
transport models, and a recently-established GIS-based WWW-site that serves as a
data repository for participating hydrometeorological agencies in South America,
Central America, and the Caribbean (R-HydroNET v1.0).
Our aim in developing the WBC-LBA is to produce
high resolution gridded fields for precipitation, temperature and other climatic
variables, evapotranspiration, soil water, drainage basin storage, runoff, and
river discharge that are consistent with the observational record of data
collected at hydrometeorological monitoring stations. We plan also to test
runoff and convergence field predictions made by an atmospheric model (i.e., the
CPTEC/COLA GCM with coupled 4DDA ETA model) applied over the experimental
domain. Both retrospective (1960-present) and LBA-contemporary time frames will
be analyzed and the results made available to the LBA research community through
the LBA-Data and Information System (DIS).
METHODS AND APPROACH
The work will be organized
around a set of supporting tasks: (a) to develop a coherent software system to
error-check, visualize, and assimilate hydrometeorological data sets, (b) to
assimilate all relevant hydrometeorological data sets, (c) to combine these data
sets with models that compute key elements of the land-based water cycle of the
Amazon Basin, (d) to validate results and identify existing gaps in our
quantitative understanding of water cycle elements across Amazonia, and (e) to
archive at the LBA-DIS and R-HydroNET the associated data sets for distribution
to the research community.
A Water Balance Closure
system for LBA (WBC-LBA) is necessary to achieve these objectives. It will
combine three existing analysis tools / data repositories:
(1) a regional, high resolution version of the
UNH Global Hydrological Archive and Analysis System (GHAAS);
(2) climatically and topographically-aided
"smart" interpolation methods for producing gridded, high-resolution
meteorological fields at the University of Delaware; and
(3) the WWW-based UNESCO Regional
Hydrometeorological data bank for South America, Central America, and the
Caribbean (R-HydroNET v1.0, developed at the University of New Hampshire) and
UNESCO ROSTLAC/LACHYCIS (Latin and Central American Hydrological Cycle and
Water Resources Activities Information System) metadata base.
Over the domain of the Amazon,
two broad determinations of water balance components will be pursued. The first
will be based on land-based forcings derived from high-resolution interpolations
of the instrumental record using methods developed by Willmott et al. (1996),
Willmott and Robeson (1995), and Willmott and Matsuura (1995). The water balance
equations as given in Vörösmarty et al. (1996,1998) will be applied in this
study with the probable addition of an explicit daily time step. Budgets such as
that shown in Table I (Vörösmarty et al. 1996) will be developed, together with
residual terms that depict the success (or failure) in closing the hydrologic
Elements of the WBM/WTM computed water balance
for the Amazon Basin, upriver of Óbidos.
Each water-year begins in September. (All units are
A second approach will rely
on aerological water balances computed using techniques developed by several
authors (Roads et al. 1994; Oki et al. 1993; Brubaker et al. 1994). In our
application, we will take convergence fields from atmospheric models,
specifically the CPTEC/COLA GCM with the coupled ETA 4DDA scheme operating over
the region at 40 x 40 km resolution and test for coherence with our
"land-based" outputs. We will also route excess water predicted from
such models and test against observed hydrography data. The entire set of
determinations made under each method will be compared and we will use this
intercomparison of calculations to highlight both consistencies and
inconsistencies in water balances in major sub-basins of the Amazon. We are also
collaborating with C. Birkett of GSFC and J. Melack of UCSB to incorporate
remotely sensed river stage and floodplain inundation estimates into the water
balance/river transport scheme.
We believe that development
of WBC-LBA and the associated analysis will lend support to several requirements
of the LBA Hydrometeorological Program. It focuses directly on the need to
develop accurate surface hydrological budgets with error terms (Priority Topic
2.2). It also supports seasonal-to-interannual predictability (e.g. Marengo
1998), analysis of the responses of the Amazon hydrograph to changes in
atmospheric forcing, the treatment of the Amazon Basin as a regional entity, and
a context to test the accuracy of atmospheric and hydrological models of the
Brubaker, K.L., D. Entekabi, and P.S. Eagleson.
1994. Atmospheric water vapor transport and continental hydrology over the
Americas. J. of Hydrology 155: 407-28.
Marengo, J.A., J. Tomasella and C.R. Uvo.
1998. Trends in streamflow and rainfall in tropical South America: Amazonia,
eastern Brazil, and northwestern Peru. J.Geophy.Res.103:1775-83.
Oki, T., K. Musiake, K. Masuda and H.
Matsuyama. 1993. Global runoff estimation by atmospheric water balance using
ECMWF data set, In: Macroscale Modelling of the Hydrosphere, W. B.
Wilkinson (Ed.), IAHS Publ., No. 214, UK., pp. 163-172.
Roads, J.O., S.-C. Chen, A. Guetter, and K.
Georgakakos. 1994: Large-scale aspects of the United States hydrologic cycle. Bull.
Amer. Met. Soc. 75:1589-1610.
Vörösmarty, C.J., C.A. Federer and A.
Schloss. 1998. Potential evaporation functions compared on U.S. watersheds:
Implications for global-scale water balance and terrestrial ecosystem
modeling. J. of Hydrology 207: 147-69.
Vörösmarty, C.J., C.J. Willmott, B.J.
Choudhury, A.L. Schloss, T.K. Stearns, S.M. Robeson, and T.J. Dorman. 1996.
Analyzing the discharge regime of a large tropical river through remote
sensing, ground-based climatic data, and modeling. Water Resources Research
Willmott, C.J., S.M. Robeson and M.J. Janis.
1996. Comparison of approaches for estimating time-averaged precipitation
using data from the USA. Int. J. Climatology 16: 1103-1115.
Willmott, C.J. and K. Matsuura. 1995. Smart
Interpolation of Annually Averaged Air Temperature in the United States. J.
Applied Meteorology 34: 2577-2586.
Willmott, C.J. and S.M. Robeson. 1995.
Climatologically Aided Interpolation (CAI) of terrestrial Air temperature. Intl.
J. Climatology 15: 221-229.
Date: May 1999