High water temperature and heavy rains in Peru

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In recent years, sea surface temperatures in the central and eastern tropical Pacific Ocean have been abnormally low, 0.5-1.0 °C below average. However, this long “triple episode” of La Niña ended in February 2023, when shifting winds halted the upwelling of cold waters off the coasts of Peru and Ecuador.

As the flow of cold water slowed in March and April 2023, surface temperatures of the Pacific Ocean rapidly rose several degrees above normal in an area extending up to a few hundred kilometers west of the coast of South America. The changes were significant enough that Peru’s National Meteorological and Hydrological Service (Senamhi) has declared that the area is now experiencing a coastal El Niño.

The map below shows sea surface temperature variations on April 4, 2023. Surface waters were about 6 °C (10.8 °F) warmer than normal off the coast of Peru on that date, based on data from multiscale high-resolution sea surface temperature ( MUR SST) project. MUR SST combines sea surface temperature measurements from various satellites from NASA, the National Oceanic and Atmospheric Administration (NOAA), and other international agencies, as well as observations from ships and buoys. (Scientists also use instruments floating in the sea to make forecasts of underwater temperatures.)

Unusually warm waters have played a role in causing heavy rains towards the coast, while northern Peru, Ecuador and parts of western Brazil have received frequent heavy rains since mid-March. The rains became particularly heavy after rising ocean temperatures helped fuel Tropical Cyclone Yaku, which dumped more rain in the normally dry region. That storm — the first tropical cyclone to hit the region in decades — was disorganized and without an eye, but dropped record amounts of rain on the semi-arid region of northern Peru on March 9, 2023. Pacasmayo dropped 13.7 cm of rain in a 24-hour period, and Chiclayo got 8.7 poison.

The warm sea surface temperatures coincided with the time of year when Peru typically experiences its highest seawater temperatures, explained Rene Garrod, an ecologist at the University of Chile. This raised sea surface temperatures above 80 °F (27 °C), accelerating evaporation, making the air wetter, and fueling the formation of high convective clouds that produce heavy rains and thunderstorms. The situation is similar to that in 2017, which was the last time the coastal El Niño event flooded the region with rain.

The Landsat satellite imagery at the top of this page shows additional water accumulating in La Niña Lake, an ephemeral lake that fills when unusually heavy rains flood the nearby Piura and La Leche rivers. The first image (above), acquired by the Operational Earth Imager 2 (OLI-2) aboard the Landsat 9 satellite, shows the same area on February 24, 2023, before the worst of the rain. The second image (below) shows the lake on March 12, 2023, when it filled with floodwaters. On March 23, a lake flood destroyed a section of a nearby highway, cutting off the towns of Parachique and Bayóvar. Floods continued to pour over the normally dry landscape in the days and weeks that followed, and satellite data showed that much of the lake was inundated by the end of the month.

The Flood caused widespread effects on Earth. According to the United Nations Office for the Coordination of Humanitarian Affairs, more than 10,000 homes have been left uninhabitable, hundreds of thousands of kilometers of water infrastructure have been damaged, and large numbers of schools have closed.

There was at least one positive outcome for all of the rains. “Satellite images show widespread greening on the Pacific side of the Andes this year, compared to the previous year,” Jarrod said.

NASA Earth Observatory images by Lauren Dauphin and Alison Nussbaum, using data from the Multiscale High Resolution Sea Surface Temperature (MUR SST) project and data from the US Geological Survey’s Landsat satellite. Reporting by Adam Voyland.