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clear overall than changes in temperature, as the
rugged topography of the Andes influences the
generalizability of precipitation measurements.
Most importantly though, the internal variability
(such as year-to-year differences) is very large for
precipitation, and therefore any climate change
signal must be very strong to be visible in this
variability (and it isn’t). The trends observed are that
precipitation has increased in the inner tropics but
decreased in the outer tropics (Magrin et al., 2014).
Bolivia and southern Peru have the biggest problems
with water shortages. The north-western coast of
Peru and the hyper-humid Ecuadorian Choco have
experienced an increase in precipitation, while the
drier Altiplano area has observed a decrease.
Changing seasonality is perhaps the most important
change in precipitation patterns observed so far. In
the south in particular, there are indications that the
rainy season has become more intense and more
seasonally concentrated, while the dry season has
become longer (Seth et al., 2010).
Precipitation in the Tropical Andes also has great
yearly and decadal variation. This is mainly due
to the El Niño Southern Oscillation (ENSO) and
Pacific Decadal Oscillation (PDO) climate systems.
It is important to remember that ENSO events have
spatially and temporally different and asynchronous
effects in different parts of the Tropical Andes.
Along the lower slopes of the Tropical Andes, El
Niño events generally cause heavy rainfall. However,
this rainfall does not reach above 2000 m.a.s.l. In
fact, El Niño events generally lead to warm and dry
weather in the high elevations of the Tropical Andes
and along the eastern slopes. La Niña events, on the
contrary, generally cause cold and wet conditions
in the high mountains. In the Central Andes,
this influence is less significant and less uniform
(Chevallier et al., 2010).
Source: National Oceanic And Atmospheric Administration
-1,50
-0,75
0
0,75
1,50
2,25
Low soil
moisture
Wet conditions
Dryer
than usual
Dry conditions
Cold ocean
layer
Warm ocean
layer
Raising of
warmmoist
air
Severe
droughts
Droughts in the Andes
Intense summer
rainfall
South East trade winds
reversed or weakened
Warmwaters
accumulates on South
America’s coast
The effect of El Niño on weather in the Andes
Cold and warm episodes
Oceanic Niño Index
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2010 2015