The Caroní river, one of the major tributaries of the Oricono, is located in southeastern Venezuela and drains an area of approximately 95,000 km2. The flow of this river shows a significant seasonal modulation, with average maximum flow in July and minimum in March. Hydroelectric power generated by dams on the Caroní supply Venezuela with over 70% of its electricity, thus making the variations in the flow of this river a key factor in the economic life of this country.

In this paper we analyze the time-series record of monthly average flow of the Caroní, as measured at Guri station from 1950 to the present, in conjunction with various standard indices of large-scale climate variability. These include the Southern Oscillation Index (SOI), various indices of seas surface temperature anomalies in the Pacific and Atlantic Ocean (such as the Niño 3 and 4 “boxes”), the Quasi-Biennial Oscillation (QBO) index, and the Wolf index of solar activity. Threshold criteria based on percentile values of the various climate indices were selected to classify individual months as pertaining to either “strong”, “moderate” or “weak” ENSO or Anti-ENSO (AENSO) (more commonly known as “La Niña”) events.

Results indicate a long-term trend toward increasing flow of the Caroní River, particularly evident for the rainy season months of June-October, in the period since 1950. Monthly anomalies in the Caroní river flow were most significantly correlated to the sea surface temperature anomalies in the Niño 34 box (located 5?N to 5?S and 170?W to 120?W). ENSO/AENSO events were found to have a significant impact on the Caroní river flow, with positive river flow anomalies corresponding to the latter. The larger the magnitude of the ENSO and AENSO events (according to our three-way classification) the greater the impact on the river flow was found to be. We also found significant influences on Caroní river flow by the QBO (negative river flow anomalies corresponding to low stratospheric wind values) and solar activity (negative river flow anomalies corresponding to low Wolf index values). Variations in these last two indices appear to modulate the influence of ENSO and AENSO events on the Caroní River flow. The implications of these results for Venezuela will be discussed.