Water Level Fluctuations in the Plata Basin (South America) From Topex/Poseidon Satellite Altimetry

Time series of water level along two major rivers of the Plata basin in South America (Parana and Paraguay) are examined using altimetry data from the Topex/Poseidon satellite over a 9-year period (1993-2001). The methodology for detecting water surfaces over continents in the radar echoes is described. Water level time series at 14 sites corresponding to intersections of the satellite tracks with the rivers, and at 7 sites corresponding to flooded areas, are constructed. The amplitude of the seasonal cycle at each site decreases with increasing latitude. The time series for the Lower Parana, Paraguay and Upper Parana differ mainly by a time-lag which suggests that perturbations in water level propagate along the rivers with a mean speed of about 0.1 ms-1. The time series at locations on the Parana near its confluence with the Paraguay differ significantly from those at locations further upstream. The interannual variability of the Lower Parana, with a strong peak in early 1998 and minima in early 1996 and 2000, is closely related to the impacts of El Ni¤o/Southern Oscillation. The Upper Parana and Paraguay show similar features with smaller amplitudes. The substantial variability of these rivers before 1995, on the other hand, cannot be straight forwardly attributed to ENSO effects. A likely reason is the variability of the South American monsoon that affects the northern part of the Plata basin. It is concluded that satellite altimetry has great promise as a technique for dense and continuous monitoring of river water levels, and thereby of regional climate variability in the basins of large rivers.