Discharge simulation in the sub-basins of the Amazon using ORCHIDEE forced by new datasets

摘要

The aim of this study is to evaluate the ability of the ORCHIDEE land surfacemodel to simulate streamflows over each sub-basin of the Amazon River basin.For this purpose, simulations are performed with a routing module includingthe influence of floodplains and swamps on river discharge and validatedagainst on-site hydrological measurements collected within the HYBAMobservatory over the 1980–2000 period. When forced by the NCC globalmeteorological dataset, the initial version of ORCHIDEE shows discrepancieswith ORE HYBAM measurements with underestimation by 15% of the annual meanstreamflow at óbidos hydrological station. Consequently, severalimprovements are incrementally added to the initial simulation in order toreduce those discrepancies. First, values of NCC precipitation aresubstituted by ORE HYBAM daily in-situ rainfall observations from themeteorological services of Amazonian countries, interpolated over the basin.It highly improves the simulated streamflow over the northern and westernparts of the basin, whereas streamflow over southern regions becomesoverestimated, probably due to the extension of rainy spots that may beexaggerated by our interpolation method, or to an underestimation ofsimulated evapotranspiration when compared to flux tower measurements.Second, the initial map of maximal fractions of floodplains and swamps whichlargely underestimates floodplains areas over the main stem of the AmazonRiver and over the region of Llanos de Moxos in Bolivia, is substituted by anew one with a better agreement with different estimates over the basin.Simulated monthly water height is consequently better represented in ORCHIDEEwhen compared to Topex/Poseidon measurements over the main stem of theAmazon. Finally, a calibration of the time constant of the floodplainreservoir is performed to adjust the mean simulated seasonal peak flow atóbidos in agreement with the observations.