El Niño Impacts from Large to Local Scale on Peruvian Rivers.

Flood occurrence is generally associated with weather and climate variability, and its damage to the population as well as infrastructure. Our study cases are two basins located in the Peruvian Pacific coast: Piura and Rimac, which are frequently affected by the El Niño phenomenon ENSO. The main objectives are: a Update the relationship between the streamflow regime and ENSO in the Piura and Rimac basins and sub-basins by a correlational and statistical approach with large scale climate variability. b Analyze the evolution of streamflow during short-duration events through a large-scale particle image velocimetry LSPIV method, able to measure flash floods through a proposed low-cost equipment SMVN with this non-intrusive approach. The analysis of the temporal relationship between ENSO indices and Piura and Rimac streamflow over four decades was carried out through running correlation method at the sub-basin scale. ENSO indices such as E index and C index presented a significant correlation with the streamflow of the Piura and Rimac basins respectively. However, in a temporal analysis, significant correlations were stronger in certain decades and a correlational change started in 2000s and offered new perspectives about streamflow surplus and deficits. Additionally, images and video analysis on events through the LSPIV method allowed a more accurate estimation of peak flows at a local scale. Chosica in Rimac and Eguiguren in Piura SMVN stations made it possible to quantify the flow rates during flash flood events. Based on these results, studying the interrelation between ENSO and streamflow during the last decades allow to identify regions with a direct and inverse impact of such phenomena. Also, the behavior of latest flash floods in 2023 with a non-intrusive hydrometrical method could allow to interpret the effects at short scale and to take actions in future flood management plans.