El Niño and La Niña: Their Impacts on Global Climate and Geomorphic Systems Kathy Lipschultz
What is ENSO? ENSO = El Niño-Southern Oscillation La Niña = cold equatorial Pacific El Niño = warm equatorial Pacific Interannual variation in sea surface temperatures and atmospheric conditions over the tropical eastern Pacific Ocean Events last 1-2 years and begins between December and February
During ENSO events El Niño SST (Sea Surface Temperature) increases, easterly trade winds weaken in the equatorial Pacific. Currents move surface water away from the western coast South America more slowly Thermocline flattens During La Niña, SST decreases, and results in opposite effects
Driving Factors Coupled interaction between the ocean and atmosphere Madden-Julian Oscillation easterly winds Kelvin waves Volcanic eruptions Affect atmospheric/oceanic circulation Changes SST
Climatic Consequences Asia El Niño increases rainfall in extratropics, weakens summer monsoons, causes droughts in SE La Niña causes floods in SE Africa Dipole in rainfall
Climatic Consequences (cont.) North America El Niño = more severe weather in southern U.S., dry monsoon seasons in Mexico La Niña = 66% chance of ≥2 hurricanes hitting cont’l U.S., wet monsoon seasons South America El Niño = droughts in Brazil in March, decreased rainfall in Amazon
Geomorphic Implications Damage to coasts and coral reef ecosystems Movement of dunes, glaciers, and mass wasting in heavy-rain areas Change in streamflow, sediment yield, and water levels in lakes
The erosion of Pacifica Cliffs in January 2016 from increased storm activity during El Niño
From slope failure after heavy rain ~$4,000,000 of damage – the most expensive landslide in U.S. history Thistle slide, Utah, 1983
A flooded football field in Arnold, Missouri after the Meremec River avulsed following days of El Niño-induced rainfall (January 2016)
In summary... ENSO has consequences for climate and, as a result, geomorphic systems These consequences are numerous and global in scale