Abstract
Abstract. The aim of this study is to evaluate the ability of the ORCHIDEE land surface model to simulate streamflows over each sub-basin of the Amazon River basin. For this purpose, simulations are performed with a routing module including the influence of floodplains and swamps on river discharge and validated against on-site hydrological measurements collected within the HYBAM observatory over the 1980–2000 period. When forced by the NCC global meteorological dataset, the initial version of ORCHIDEE shows discrepancies with ORE HYBAM measurements with underestimation by 15% of the annual mean streamflow at Óbidos hydrological station. Consequently, several improvements are incrementally added to the initial simulation in order to reduce those discrepancies. First, values of NCC precipitation are substituted by ORE HYBAM daily in-situ rainfall observations from the meteorological services of Amazonian countries, interpolated over the basin. It highly improves the simulated streamflow over the northern and western parts of the basin, whereas streamflow over southern regions becomes overestimated, probably due to the extension of rainy spots that may be exaggerated by our interpolation method, or to an underestimation of simulated evapotranspiration when compared to flux tower measurements. Second, the initial map of maximal fractions of floodplains and swamps which largely underestimates floodplains areas over the main stem of the Amazon River and over the region of Llanos de Moxos in Bolivia, is substituted by a new one with a better agreement with different estimates over the basin. Simulated monthly water height is consequently better represented in ORCHIDEE when compared to Topex/Poseidon measurements over the main stem of the Amazon. Finally, a calibration of the time constant of the floodplain reservoir is performed to adjust the mean simulated seasonal peak flow at Óbidos in agreement with the observations.
Highlights
The Amazon River basin, the largest basin in the world with an area of approximately 6.0 million km2, has the highest average discharge (206 000 m3 s−1) (Callede et al, 2010) and it contributes to about 15–20 % of the fresh water transported to the oceans (Richey et al, 1986)
Flooded fraction extension cannot be com- tracted each month to the water level height from the simupared with observations as long as the swamps do not have lated and observed data. a spatio-temporal variability simulated in ORCHIDEE
The simulation by ORCHIDEE of discharge values in the main tributaries of the Amazon River basin and in the last gauged station Obidos has benefited from two major inputs
Summary
The Amazon River basin, the largest basin in the world with an area of approximately 6.0 million km, has the highest average discharge (206 000 m3 s−1) (Callede et al, 2010) and it contributes to about 15–20 % of the fresh water transported to the oceans (Richey et al, 1986). At the beginning of 21st century, a distributed Large Basin Simulation Model, called MGB-IPH (an acronym from the Portuguese for Large Basins Model and Institute of Hydraulic Research), was developed by Collischonn and Tucci (2001) Applications of this model were initially developed for the La Plata basin (Allasia et al, 2006) and for some Amazonian rivers, the Madeira (Ribeiro et al, 2005), the Tapajos, where satellitederived rainfall information is being used to run the model (Collischonn et al, 2008), and the Negro river, where spatial altimetry data is being used to complement the validation of the simulation (Getirana, 2010; Getirana et al, 2010)
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