Calculations of river-runoff in the GISS GCM: impact of a new land-surface parameterization and runoff routing model of the Amazon River

Climate Dynamics 10 (1994) 6/7, 349-361, by F Abramopoulos:

· The study examines the impact of a new land-surface parameterization and a river routing scheme on the hydrology of the Amazon basin, as depicted by the NASA/Goddard Institute of Space Studies (GISS) global climate model (GCM).

· The more physically realistic land surface scheme introduces a vegetation canopy resistance and a six-layer soil system. The new routing scheme allows runoff to travel from a river's headwater to its mouth according to topography and other channel characteristics and improves the timing of the peak flow.

· River runoff is examined near the mouth of the Amazon and for all of its sub-basins. With the new land-surface parameterization, river runoff increases significantly and is consistent with that observed in most basins and at the mouth.

· One positive impact of the new land-surface parameterization is that it produces more realistic evaporation over the Amazon basin, which was too high in the previous version of the GCM. The realistic depiction of evaporation also affects the thermal regime in the lower atmosphere in the Amazon.

· In fact, the lower evaporation in some portions of the basin reduces the cloudiness, increases the solar radiation reaching the ground, increases the net radiation at the surface, and warms the surface as compared to observations. Further GCM improvement is needed to obtain a better representation of rainfall processes.