The El Niño-Southern Oscillation (ENSO) is a major global climate phenomenon driven by fluctuating ocean temperatures in the central and eastern equatorial Pacific Ocean. El Niño represents the warm phase of this cycle, characterized by an abnormal warming of the Pacific sea surface temperatures near the equator, which disrupts normal atmospheric and oceanic circulation patterns. For South America, El Niño acts as a powerful driver of extreme weather, leading to a variety of geographically specific impacts across the continent.
Effects on the Pacific Coastal Zone
The most direct and immediate effects of El Niño are felt along the Pacific coasts of Ecuador and Peru, where the warm water pool approaches the South American continent. This warming disrupts the normal process of upwelling, where cold, nutrient-rich water from the deep ocean rises to the surface. Under normal conditions, this upwelling, driven by the Humboldt Current, supports one of the world’s most productive marine ecosystems.
The influx of warmer, nutrient-poor surface water deepens the thermocline, preventing the rise of cold water and causing a massive disruption in the marine food web. Phytoplankton, the base of the ocean food chain, cannot flourish without the necessary nutrients, leading to a collapse in primary production. This severely impacts the anchovy and sardine populations, which are fundamental to the regional fishing economy.
Atmospherically, the warmer sea surface temperatures create instability, leading to intense and unseasonal rainfall along the northern coasts of Peru and Ecuador. The resulting torrential rains can cause catastrophic flooding, mudslides, and damage to infrastructure in coastal cities. This excessive precipitation and the subsequent flooding can destroy roads, bridges, and ports, severely impeding transport and regional commerce.
Drought in the Amazon Basin and Northern Interior
In stark contrast to the flooding on the Pacific coast, El Niño conditions often shift the rainfall patterns away from the Amazon Basin and northern interior regions of South America. Countries like Colombia, Venezuela, and parts of the Brazilian Amazon experience significantly reduced precipitation, leading to prolonged drought conditions. This lack of rainfall causes river levels, including major Amazon tributaries, to drop dramatically, sometimes reaching their lowest levels in over a century.
Severely low river levels disrupt the primary transportation network for communities deep within the Amazon, isolating villages and making the import of goods and food difficult. The drought also increases the frequency and intensity of wildfires, as the forest ecosystem experiences severe moisture deficit. The stress on the forest can cause it to turn into a net carbon source, releasing stored carbon dioxide.
The reliance of many South American nations on hydroelectric power makes the drought a significant energy security issue. For instance, Brazil, Colombia, and Ecuador rely heavily on river flow for a large percentage of their electricity generation. When river basins dry up, the capacity of hydroelectric dams is severely curtailed, leading to power cuts and energy rationing in major cities. The San Rafael reservoir near Bogotá, Colombia, for example, has seen its water level drop drastically, necessitating urban water rationing for millions of residents.
Increased Rainfall in the Southern Cone
While the equatorial and northern regions face drought, the southern part of the continent, known as the Southern Cone, typically experiences the opposite effect. El Niño is strongly associated with above-average precipitation and sometimes cooler conditions across Northeastern Argentina, Uruguay, and Southern Brazil. This meteorological shift signals increased rainfall variability in the region.
The excessive rainfall often results in major river flooding, particularly along the Paraná and Uruguay River systems. The sheer volume of water flowing from southern Brazil can cause the rivers to breach their banks, leading to the displacement of tens of thousands of families in neighboring countries like Paraguay and Argentina. The city of Concordia in Argentina, for example, has experienced severe flooding as the Uruguay River reached levels not seen in decades.
This increased precipitation can overwhelm regional infrastructure and urban drainage systems. The physical consequences include widespread damage to homes and businesses, necessitating large-scale evacuations and the establishment of temporary shelters. The prolonged intensity of these flood events causes significant challenges for local authorities managing the disaster and providing continuous aid.
Economic and Public Health Ramifications
The diverse weather patterns caused by El Niño translate into significant economic and public health costs that span the entire continent. The agricultural sector is often the hardest hit, accounting for an estimated 85% of economic losses during these events. Crop failures occur both from prolonged drought in the north, affecting staple crops like maize and rice in Colombia and Venezuela, and from excessive flooding in the south, which destroys harvests and infrastructure.
Infrastructure damage from both flooding and drought also incurs substantial financial burdens, including the repair of roads, bridges, and ports. Beyond direct damage, the collapse of key industries, such as the Peruvian and Ecuadorian anchovy fisheries, destabilizes local economies and impacts international trade. These widespread losses contribute to food insecurity, especially for communities reliant on agriculture for their livelihood.
Public health risks are significantly amplified by the altered climate conditions. Higher temperatures combined with changes in standing water—from floodwaters or new breeding grounds created during drought—favor the proliferation of disease vectors. This leads to an increased incidence of vector-borne diseases such as Dengue, Zika, and Malaria across affected regions. Waterborne diseases like cholera and leptospirosis also become more common due to water contamination from flood events.