Fingerprinting 'El Nino Costero': a unique opportunity to document the signature of an extreme flood event in northern Peru

The northern coast of Peru has been experiencing anomalously warm (4-5C) sea surface temperatures (SST). These high SSTs have produced intense and prolonged rainfall that has resulted in extensive flooding, and on the 26th March 2017, the Rio Piura in northern Peru burst its banks leading to loss of life, displacement of people and damaged infrastructure. Peru is intimately linked to the El Niño-Southern Oscillation (ENSO): fishermen first identified El Niño in the late 19th Century off the north coast of Peru. The phenomenon driving this current acute rainfall event has been dubbed 'El Niño Costero' or Coastal El Niño, but is not El Niño per se as it is not being driven by anomalous SSTs in the central Pacific (Niño 3.4), which generally defines the onset of El Niño. Rather it represents more local (Niño1+2) El Niño-like conditions last known to have occurred in 1925, which is considered the most intense flooding of the 20th Century. Despite Peru's preparedness for the global El Niño in 2016, the country appears to be overwhelmed by the sudden shift from La Niña drought to the intense rainfall of El Niño Costero, suggesting this type of locally driven El Niño event has hitherto been overlooked. It is essential to establish a record of El Niño Costero alongside ENSO, especially as the 1925 event was the most extreme on record. If local SSTs cause El Niño-like conditions and play an important part in climate dynamics in northern Peru, but have so far been overlooked, then we don't have a full understanding of tropical Pacific climate change. Critical to understanding equatorial Pacific climate change are records of extreme flood events that reflect El Niño-type behavior, and in particular how El Niño Costero fits within the wider climate picture. This proposal is based on a unique opportunity to quantify and determine the dynamics and evolution of a large magnitude flood, and to use its sedimentary signature, coupled to climatological data over the last 120 years, to unequivocally fingerprint and calibrate past El Niño-type events in recent lake sediments. We will (a) undertake a geophysical survey of lakes in the Rio Piura catchment that act as repositories of flood-waters and sediments, and we will identify modern flood sediments and determine their depth and extent; (b) recover and survey surface sediments related to flooding to characterize their flood signature using grain size, geochemistry and mineral magnetics; (c) recover and date short sediment cores from our survey lakes and directly compare the flood signature of the 2017 El Niño Costero to the 1925 event, as well as putting it in the context of 20th Century ENSO variability. Our study will provide a framework for reconstructing El Niño-related flood events from lake sediments over the recent past in northern Peru, but has the potential to establish a much longer-term (Holocene and older) history of all El Niño variability in the region.

"Few countries were better prepared for the recent global El Niño than Peru so it is doubly concerning that the country has been overwhelmed by this occurrence of local El Niño-like conditions which have flipped the country from widespread drought to enormous flooding that has taken dozens of lives, affected over half a million people and left many homeless."

Robert Glasser, UN Special Representative of the Secretary-General for Disaster Risk Reduction

The main groups who will benefit from our research in the Rio Piura basin are the local communities, non-governmental organisations, municipalities and regional governments. For example, the benefit derived from a greater understanding of the impacts of El Niño on lake hydrology, river discharge and sediment dynamics will guide Practical Action's (Peru-based NGO specialising in disaster risk management and resilience) design and sustainability of interventions aimed at building resilience in vulnerable communities with in the Piura basin. With the help of our data, they will be able to identify reaches of the Piura River most at risk from flooding and geomorphic change. Furthermore, Practical Action is currently engaged with developing an Early Warning System, with key attributes of such a system are understanding the frequency and magnitude of El Niño events, especially flooding that sits outside ENSO variability. Therefore understanding the dynamics of the Piura basin is essential. Overall our efforts will lead to increased resilience to flooding and promoting informed decisions for future El Niño events.