Extreme flood in Peru during early 2017

Abstract

From December 2016 to March 2017, a series of downpours and record precipitation events caused severe floods over the Pacific coast of Peru, causing hundreds of casualties and billions in economic loss. This series of floods was developed in association with recurrent patterns of, but unusual strengthen in, the atmospheric and oceanic conditions including warmer than normal local sea surface temperature (SST) and weakened trade wind. These climatic features and their causal relationship between the anomalies of equatorial wind, SST and precipitation were examined. Observational diagnoses and model experiments suggest that an atmospheric forcing in early 2017, which was moderately linked to the Trans-Niño Index (TNI), initiated local SST warming off coastal Peru and over the equator. This SST warming provided positive feedback to the continual weakening of the trade wind, which led to onshore wind in March causing enhanced rainfall over northwestern Peru. Given the empirical relationship between the boreal winter rainfall in Peru, local SST warming and weakened trade wind, climate projection produced by large-ensemble simulations suggest that anthropogenic climate change will enhance the flood risk in Peru through increased coastal SST and a southward shift in the intertropical convergence zone.