A RECENT INCREASING TREND IN THE STREAMFLOW OF RIVERS IN SOUTHEASTERNSOUTH-AMERICA

This paper examines the records of streamflow during the period 1901-9 5 corresponding to four major rivers in southeastern South America: Ur uguay, Negro, Parana, and Paraguay. The emphasis is on the detection o f long-term trends in the records. The authors demonstrate that the 30 -yr running averaged streamflows increased after the mid-1960s at a ra te that is approximately linear but not the same in all rivers. There seems to be a tendency reward leveling off in the most recent values. The increased streamflow is consistent with a significant decrease in the amplitude of the seasonal cycle in all rivers, except in the Negro River. An analysis of the sea surface temperature in the eastern equa torial Pacific Ocean suggests that an important component of such an i ncrease in streamflows is consistent with a large-scale and low-freque ncy variability of the climate system.