Reduction of flows due to the implementation of hydroelectric systems in the Chiriquí Viejo River Basin, Panamá

This research examines the combined impacts of hydroelectric regulation and flow retention, together with extreme climatic events, on the hydrological dynamics of the Chiriquí Viejo River basin, Panama. Daily stream flow records from 1984 to 2021 were analyzed at two stations: 102-001 (upstream of the hydroelectric system) and 102-102 (downstream of the hydroelectric system), capturing the influence of seven hydroelectric plants operating along the basin. Results show that from 2010, when these plants began operations, the mean annual flow at station 102-001 decreased from 7.73 m³/s to 4.76 m³/s (38.4%), while at station 102-102 it declined from 67.2 m³/s to 35.1 m³/s (47.8%), confirming a structural alteration of the natural flow regime associated with hydroelectric regulation. In addition to these long-term changes, extreme hydrometeorological events intensified hydrological variability within the basin. In November 2020, during hurricanes Eta and Iota, flows at the downstream station exceeded 120 m³/s, representing a maximum monthly increase of 1332.8% relative to typical baseflow conditions, surpassing system regulation capacity and generating significant hydrological stress. These findings demonstrate that hydroelectric regulation and flow retention, combined with extreme hydroclimatic events, have reconfigured flow dynamics, reducing hydrological resilience, altering seasonal patterns, and increasing system vulnerability.