Why is Peru suffering coastal landslides and flooding?

The above image of a woman struggling to escape mud and debris-filled floodwater has spread around the world, and come to symbolise the climatic tragedy that Peru is currently facing. To date, 94 people have died, and an estimated 700,000 have been left homeless, as a direct result of the landslides and flooding, brought on by unusually heavy rains on the Western side of the Andes.

Flooding in Plaza de Armas, Trujillo on night of 15th March, 2017, as a result of El Niño rains. Courtesy of Diego Alonso. 

Northern coastal cities, such as Trujillo and Piura have been particularly hard hit, while a number of districts of Lima have been devastated by rivers - that are usually little more than trickles - bursting their banks. Even in the more affluent areas of Lima, such as Miraflores and San Isidro, the water supply has been cut intermittently, as SEDAPAL, the state entity that manages drinking water in the city, has been unable to cope with the massive amounts of extra water entering their reservoirs. 

What, then, is causing all this destruction? To understand this, we need to look at Peru's coastal climate which, in a similar way to southern California, blends strong desert and offshore influences.

The famed Humboldt Current sweeps up the South American coast from the Antarctic, bringing with it cold water that wells up to create rich fishing grounds and cooler air along the shore. This also creates perfect meteorological conditions for the formation of a marine layer and coastal mist or fog ... but not clouds that would dump any significant amount of rain onshore. In fact, the Humboldt is the primary reason that Peru has a desert coast.

A thick mist (garúa) tends to form during the southern hemisphere winter (May to November) when Lima, and other southern coastal cities, can sometimes go days at a time without seeing the sun.

During the summer, coastal daytime temperatures tend to range from 25º - 28ºC (77º - 83ºF); during the winter it can get significantly cooler, with daytime highs averaging 12º - 15ºC (54º to 59ºF).

But then, every few decades the legendary El Niño Current unexpectedly drops down from the equatorial Pacific, bringing with it much warmer temperatures and monsoon-like conditions. Although the dreaded fog dissipates and rains fall on the coastal desert, El Niño also ushers in flash floods and mudslides.

Also called the Southern Oscillation, this intermittent disruption of the weather and water conditions in the tropical eastern Pacific, was first detected by 19th century Peruvian fisherman, who noticed a warm current suddenly flowing down from the Equator and blunting the much cooler Humboldt Current. Because the mysterious current always arrived around Christmas, they dubbed it El Niño (“The Little Boy”), after the Christ Child.

It was not until the 1980s that scientists discerned that the oscillation had a major impact on weather patterns all around the Pacific Basin, including increased rainfall in Peru and the southern U.S. and drought conditions in Australia and Indonesia. It sometimes occurs every year and at other times every three or four years. But nobody has yet to determine why El Niño is so unpredictable ... or even why it comes into existence.

El Niño Floods, Peru 2017 - Huarmey

The last major El Niño event to hit Peru was in 1997 - 98, but the human cost this time round has been exacerbated by population growth, combined with weak town planning and building regulations, which have seen the growth of cities into areas that are particularly vulnerable to increased rainfall, such as near dry river beds.

There is also a growing realisation that there has been inadequate investment in infrastructure designed to cope with these intermittent events. Critics point to the fact that 159 bridges have so far been washed away, suggesting that they were not fit for purpose.

They also look at Ecuador, which has been affected by the same El Niño rains, but where the level of destruction and loss of life has been far lower, as more preventative measures had been put in place. 

Rain is forecast to continue for at least the next two weeks, at least, and it will only be when these have finally stopped that the full impact of the emergency can be assessed.

Moreover, there is a fear that some of Northern Peru's many archaeological treasures, such as Chan Chan or Sipan, may have been damaged by the flooding. In any case, they are already suffering from a steep drop-off in visitors, with access now difficult in many cases and tourists understandably not keen to travel to disaster zones. 

However, the waters will subside soon and life will gradually return to normal. One of the best ways to help the affected areas is to spend tourist dollars (or Euros or £!) there as soon as possible.