Transcript tropical climate 8-2.. - Michigan State University

Tropics
Regions between 23.5 ° N and S (tropics of
Cancer and Capricorn). These are areas where
the sun is directly overhead at some point
during the year.
This area includes 40-50% of the globe’s surface
area (including both land and oceans).
Some defining characteristics of most
tropical areas
Warm temperatures
Biological complexity (many species and thus
many species interactions)
Many soils with low levels of mineral nutrients
In temperate areas (like Michigan), low
temperatures and low soil moisture in winter
constrain biological processes, like the growth
and reproduction of individuals
In tropical areas, other factors like biological
interactions and low soil nutrients may take
over this constraining role
Terrestrial tropical ecosystems vary greatly
Rain forests (these get most of the attention)
Deciduous forests
Scrub forests
Savanna
Mangroves
Holdridge life zones (1947)
Based classification of life zones on
1. Biotemperature (based on temperatures
starting at 0° C--below 0° C plants are
dormant)
2. Precipitation
3. Ratio of mean annual potential
evapotranspiration to mean total annual
precipitation.
Evapotranspiration is evaporation from ground
surface plus the water released from plant
leaves (transpiration)
When ratio of annual evapotranspiration to
annual precipitation is more than 1, what can
we say about the climate?
http://www.city-data.com/states/Michigan-Climate.html
Detroit’s annual rainfall is about 32.9 inches or
836 mm per year
Detroit’s daily average temperature of 49
degrees F or 9 degrees C
A strong influence on tropical climates is the
Intertropical Convergence Zone (ITCZ)
Easterly winds from north and south converge
near the equator to produce a low pressure
area
This band of low pressure shifts north and south
over the year according to where the earth is
in relation to the sun (to changes in solar
angles and radiation)
ITCZ does not cover the same area (or latitude
range) in different areas of the globe—
because of features like mountains
The shifting location of the ITCZ over the
year leads to varying patterns of rainfall
When ITCZ is present, rainfall is heavy
Rainfall diminishes as ITCZ leaves a region
Since the ITCZ is in the vicinity of the equatorial
regions (O° latitude) yearround, these
regions tend to be wet year round, often with
two “rainy” seasons
Further from the equator (20° latitude), ITCZ is
not in the vicinity as much of the year. These
regions often are somewhat drier and have
one “rainy” season
Tropical Rain Forests
Image source: Pearson Education, Inc.
Troipical rain forests.
Tropical Savanna
Image source: Pearson Education, Inc.
Tropical savanna.
Conclusions from two previous
slides
1. Tropical rain forests and savannas are not
very seasonal with regard to temperature.
2. Tropical rain forests and savannas both show
seasonal precipitation patterns
3. Seasonal precipitation patterns are more
pronounced in tropical savannas.
There is much variability in rainfall, even within
an ecosystem type (like savannas), because of
features like mountains
El Niño Southern Oscillation Cycle (ENSO)
influences tropical climates
Multi-year cycle of surface air pressure changes
in the tropical Pacific Ocean, resulting in
changes in ocean temperature
El Niño events happen every 2-8 years and vary
greatly in strength
In a normal year, pressure systems are as above. Trade winds over the Pacific Ocean move from east to west. The easterly
trade winds bring warm surface waters westward, bringing convective storms to Indonesia and coastal Australia. Along the
coast of Peru, cold bottom water wells up to the surface to replace the warm water that is pulled to the west.
http://www.physicalgeography.net/fundamentals/7z.html
In an El Niño year, air pressure drops over large areas of the central Pacific and along the coast of South America.
The normal low pressure system is replaced by a weak high in the western Pacific (the southern oscillation). This
change in pressure pattern causes reduced trade winds. This reduction means warm ocean water along the
coastlines of Peru and Ecuador. This accumulation of warm water causes the thermocline to drop in the eastern part
of Pacific Ocean which cuts off the upwelling of cold deep ocean water along the coast of Peru.
http://www.physicalgeography.net/fundame
ntals/7z.html
Three phases in ENSO cycle
El Niño phase—warm ocean surface
temperatures
La Niña phase—cool ocean surface
temperatures
Normal phase—normal surface temperatures
Strong El Niño years generally lead to
Dry periods in rain forests, which influence
biological systems:
These dry periods can lead to mass flowering in
Indonesian and Malaysian forests, then fruiting,
then the appearance of many animals following
the fruiting cycle
In other tropical areas, these dry periods can lead
to tree mortality
Predicted effects of El Niño
http://www.eoearth.org/images/b/b2/El_nino_global_map.gif
Throughout the course, keep in mind that the
“tropics” are not the same from place to place
Much variability, so generalizations are often
difficult
Major rain forest regions
Neotropics
Main
Amazon
Geographical River basin,
Feature
Andes
Bromeliad
ephiphytes,
high bird
Distinctive
diversity,
biological
small
features
primates
Africa
Southeast
Madagascar Asia
Peninsula
and islands
Congo River Forests in
on Sunda
basin
east
Shelf
Low plant
Dipterocarp
richness,
tree family,
forest
mast fruiting
elephants,
Lemurs, low of trees,
many forest fruit
large
browsers
abundance
primates
Annual
rainfall (mm) 2000-3000
1500-2000
2000-3000
Largest
Country
Democratic
Republic of
Congo
Malagasy
Republic
Brazil
From the Times Atlas of the World 1994
New Guinea
Large,
mountainous
island
Marsupial
mammals,
birds of
paradise
2000-3000, 2000-3000,
often > 3000 often > 3000
Indonesia
Papua New
Guinea
Major rain forest regions
Neotropics
Main
Amazon
Geographical River basin,
Feature
Andes
Bromeliad
ephiphytes,
high bird
Distinctive
diversity,
biological
small
features
primates
Africa
Southeast
Madagascar Asia
Peninsula
and islands
Congo River Forests in
on Sunda
basin
east
Shelf
Low plant
Dipterocarp
richness,
tree family,
forest
mast fruiting
elephants,
Lemurs, low of trees,
many forest fruit
large
browsers
abundance
primates
Annual
rainfall (mm) 2000-3000
1500-2000
2000-3000
Largest
Country
Democratic
Republic of
Congo
Malagasy
Republic
Brazil
From The Times Atlas of the World 1994
New Guinea
Large,
mountainous
island
Marsupial
mammals,
birds of
paradise
2000-3000, 2000-3000,
often > 3000 often > 3000
Indonesia
Papua New
Guinea
(Wettest areas of Michigan receive 1000 mm)
Major rain forest regions
Neotropics
Main
Amazon
Geographical River basin,
Feature
Andes
Bromeliad
ephiphytes,
high bird
Distinctive
diversity,
biological
small
features
primates
Africa
Southeast
Madagascar Asia
Peninsula
and islands
Congo River Forests in
on Sunda
basin
east
Shelf
Low plant
Dipterocarp
richness,
tree family,
forest
mast fruiting
elephants,
Lemurs, low of trees,
many forest fruit
large
browsers
abundance
primates
Annual
rainfall (mm) 2000-3000
1500-2000
2000-3000
Largest
Country
Democratic
Republic of
Congo
Malagasy
Republic
Brazil
From The Times Atlas of the World 1994
New Guinea
Large,
mountainous
island
Marsupial
mammals,
birds of
paradise
2000-3000, 2000-3000,
often > 3000 often > 3000
Indonesia
Papua New
Guinea
Major rain forest regions
Neotropics
Main
Amazon
Geographical River basin,
Feature
Andes
Bromeliad
ephiphytes,
high bird
Distinctive
diversity,
biological
small
features
primates
Africa
Southeast
Madagascar Asia
Peninsula
and islands
Congo River Forests in
on Sunda
basin
east
Shelf
Low plant
Dipterocarp
richness,
tree family,
forest
mast fruiting
elephants,
Lemurs, low of trees,
many forest fruit
large
browsers
abundance
primates
Annual
rainfall (mm) 2000-3000
1500-2000
2000-3000
Largest
Country
Democratic
Republic of
Congo
Malagasy
Republic
Brazil
From The Times Atlas of the World 1994
New Guinea
Large,
mountainous
island
Marsupial
mammals,
birds of
paradise
2000-3000, 2000-3000,
often > 3000 often > 3000
Indonesia
Papua New
Guinea
Over 30 species of gliding species in
Borneo
None in the Amazon
A few in Africa
Why?
It could be that the dipterocarp trees that
dominate Bornean forests produce fruit at
unpredictable intervals, making food harder to
find in these forests than in other tropical
forests. Therefore, many species have evolved
gliding to be able to range more widely in
search of food.