Peru’s Coastal Desert Holds El Nino Clues

PULLMAN, Wash–Where do you look for clues to ancient El Nino floods? In one of the planet’s driest spots.
Gary Huckleberry, a Washington State University geoarchaeologist, made his first reconnaissance of Peru’s hyperarid coastal desert last summer and hopes to return again over the next two years to analyze a series of flood deposits that date to 2,500 years ago. “There are few places in the world where a rich history of complex societies coincides with an area so greatly affected by El Nino,” he explains.
Peru is the origin of the term, coined by the fishermen who harvest the rich marine resources off the coast. Cold water welling up from deep regions of the Pacific carry organisms on which the plentiful food chain off the coast of Peru is based. Most years around Christmas, warmer and less fertile surface water flows south from Ecuador and harvests decline. Fishermen called the seasonal episodes El Nino, or the Christ Child.
However, scientists recently began to examine the extreme episodes of this spread of warm water from the areas of the equator to the north and south, often with catastrophic weather consequences throughout the Pacific. These dramatic changes are now popularly referred to as El Nino. Scientists know it as the warm phase of the El Nino-Southern Oscillation.
North coastal Peru’s unique climate and topography make it a special study site.
The narrow strip of land between the ocean and the Andes Mountains, averaging about 10 miles wide, is a cold fog desert. The temperature of the ocean is so cold the winds coming off them pick up little moisture, not enough to produce rain. There are other regions like this along the west coasts of continents–notably Mexico’s Baja Peninsula and the Namibian Desert of Africa.
Rainfall on Peru’s coastal desert averages less than 2 inches a year, and in some regions no measurable precipitation is recorded in decades. But during extreme El Nino years, when warm surface water provides the source of moisture, rainfall can be devastating. At Trujillo, 400 miles north of Lima, between 1918 and 1925, total rainfall was only 1.4 inches. In March 1925 the region was deluged with 15.5 inches, ravaging the area. Many regions of the country’s coast are experiencing those conditions again this year.
Despite being described as a cold fog desert, the environment is not uncomfortable, says Huckleberry. Temperatures don’t vary much throughout the year, staying at 60-80 degrees. Along the river valleys, fed by the permanent snowpacks of the 18,000-foot Andes range, farmers need not worry about frosts and can bring in two harvests a year.
“Away from the rivers the dryness is extraordinary,” says Huckleberry. By comparison, the deserts around Tucson, where he earned his geology doctorate at the University of Arizona, and other areas of the American Southwest where much of his research has focused, seem almost tropical.
The cultural development of the area provides context for the study. The earliest civilizations of the New World developed along these coastal plains. Agriculture is believed to have begun more than 4,000 years ago. The earliest prehistoric civilizations formed about 1,200 B.C., 2,500 years before the Inca culture dominated a substantial part of the South American continent.
Huckleberry hopes to conduct his excavations at a site called Quebrada de Los Chinos in the Moche River Valley, located in the northern part of the country near Trujillo, Peru’s second largest city with 1.2 million people. Farming has been conducted along the Moche for many centuries.
There is plenty of evidence of prehistoric flooding of the Moche River, but those occurrences are more likely associated with heavy precipitation in the mountains above 1,000 feet and not El Nino events, Huckleberry explains.
Quebradas are the river tributaries that appear mostly as dry canyons. Prehistoric farmers tapped the Moche at higher elevations and diverted the water through canals across the dry slopes to sections within the quebradas where they planted corn, cotton and other crops.
The hyperarid climate made these canals largely immune from floods, except for the rare El Nino events when heavy rains washed the land below 1,000 feet elevation. When those occurred, the debris would collect in areas where the flood waters lost their velocity.
Locating sites such as these was the object of Huckleberry’s reconnaissance last summer. The most promising location is a 100-meter-long streamcut at the mouth of Quebrada de Los Chinos. Exposed is a 12-foot-high bank of sand, with periodic thin layers of organic material.
The organic plant residue came from early irrigated plots, Huckleberry explains. Intermixed with the organics are charcoal and cultural materials, primarily pieces of ceramic pottery which archaeologists have documented in detail according to evolving civilizations developing there. Radiocarbon techniques date the age of the charcoal.
Preliminary analysis indicates 11 distinct floods associated with El Nino events over a period of 2,500 years, Huckleberry said. A detailed analysis could provide insight into the frequency of flooding by centuries or even decades.
That knowledge could represent a small piece of the enormously complex puzzle of global climate change and perhaps explain how increasing emissions of greenhouse gases will affect the frequency and magnitude of El Nino.
The project is also relevant to the archeological research community, says Huckleberry, because El Nino had significant effects on prehistoric complex societies. “Clearly, human societies in the past have adapted to climatic variability. A possible adaptation to El Nino events may have been an increase in political centralization in order to deal with the labor necessary to repair infrastructure damaged by El Nino floods.”

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