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SH-03 Abstract

A Water Budget Closure System to Support LBA Hydrometeorology and Ecology Studies

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).



    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


mm yr-1).


Variable 1979-80 1980-1 1981-2 1982-3 1983-4
Precipitation 2229 2306 2450 2200 2323
Evapotranspiration 1194 1210 1260 1263 1180
Runoff 1042 1091 1211 953 1131
Discharge 1030 1038 1222 975 1022
Basin Storage +5 +58 -32 -38 +121


    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.

Expected Impacts:

    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

Amazon system.




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.

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

32: 3137-50.

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


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