BIO C322 – Ecology
Insolation, Precipitation, Climate
Weather vs Climate
• Weather: State of atmosphere at a given
time & place w.r.t. temperature, humidity,
wind & air pressure.
• Climate: Long-term weather (30-40 years).
- Microclimate: Immediate; climate on a
very local scale, differing from general
climate of the area.
- Macroclimate
Examples of Microclimate
• Dense vegetation on ground influences temp, humidity
& wind  favourable environment for ground-dwelling
animals.
• On a sunny but chilly day in early spring, flies over sap
oozing from maple stump  radiation of the absorbed
solar energy.
• In northern hemisphere, north sides of tree trunks,
mountains, buildings cooler & moister than south sides
(because south side faces equator)  more vigorous
moss growth.
Sun: The Source of Energy…
Photosynthesis & Heating
41H + 2e-  4He + 2 Neutrinos + 6 Photons + Energy (EM)
The Electromagnetic Spectrum
PAR = Photosynthetically Active Radiation = 400-700 nm
Solar Radiation
• UV, visible and IR.
• ~150 millionth of sun’s energy reaches earth’s
atmosphere – Small size of earth & large
distance.
• Radiant energy reaching earth:
10% UV, 45% visible (400-700 nm), 45% IR.
• <1% converted to biomass by photosynthesis.
• Remaining not wasted but used. How?
Solar Flux
• Solar flux: Radiant energy crossing unit
surface area per unit time.
• Flux reaching earth’s atmosphere
= 2 cal/cm2/min.
• Diurnal variation in flux: earth’s rotation.
• Seasonal variation: earth’s revolution.
Fate of Solar Radiation
Thought Question
• Photosynthesis can continue even on
cloudy days. Why?
Albedo
• Ratio of reflected light to incident light.
• Or, fraction of solar energy reflected from
an object.
• If albedo = 0, the object is dark/black.
• If albedo = 1, object is bright/white.
Which has greater albedo: Ice or Water?
Blue Lakes vs Green ones
Light falling on a Water Body
Inferences
• Blue light most penetrating  reflected 
Blue lake.
• Lights of other ʎ
absorbed/scattered/extinguished.
• Sometimes, due to suspended material,
green is reflected  Green lake.
• Most aquatic organisms reside in upper
regions of lakes & oceans. Why?
Light in Forests
• Major portion of insolation absorbed by
tree vegetation (canopy).
• Ground vegetation receives ~2-10% light.
• Forest colour: yellow-green, reddish, etc
depending on  absorption, reflection,
shade.
• “Open-gap structure”: Movement of leaf
canopy  sun-flecks make light available
to ground flora.
Diurnal Changes in Temperature
• Change minimal in aquatic environment.
Why?
• On a hot June afternoon in a desert area,
where do you find max & min temp: air,
ground surface, below ground?
Animal Adaptations to Temperature
Annual Changes in Water Temperature
• Water is most dense at 4°C (heaviest).
• Overturn: Sinking of denser water.
• Thermal stratification occurs during summer in
temperate lakes.
- Upper  Warm water (Epilimnion).
- Middle Steep temp drop (Thermocline/
Metalimnion); barrier to nutrient exchange.
- Lower  Cold water (Hypolimnion).
overturn
overturn
Water Temperature Profile of the Lake
Air Temperature
• Air temperature decreases on moving
away from earth’s surface. Why?
- Higher air density at surface, collision of
air molecules, rise in temp.
- Decline in “warming effect” of earth’s
surface.
Global Wind Patterns
•
•
•
•
•
Air movement from high to low pressure.
Equatorial region receives max solar rad.
Warm air rises as it is less dense.
Air mass spreads N & S, cooling & sinking:
Trade winds towards equator (Sailorfriendly), Westerlies & Polar easterlies.
• At 60° N & S, westerlies collide with polar
easterlies  Low Pressure  Frontal uplift.
• Deflection in pattern of air flow due to
spherical earth & spin  Coriolis effect.
WEST
ITCZ: Inter Tropical
Convergence Zone
EAST
Local Winds
• Land breeze: from land to sea; at night.
• Sea breeze: from sea to land; daytime.
• Principle:
• Land absorbs & radiates heat faster than
water.
• Water releases heat over a longer period
of time.
Local Winds: Sea Breeze
Precipitation – Hydrologic Cycle
• Condensation of atmospheric water vapour
into drops, heavy enough to fall.
• Hydrologic Cycle:
– Precipitation
– Evaporation
– Transpiration
– Vapour transport
– Surface runoff
– Groundwater flow
• Cycle in steady state: Total evap = Total
precip (but disbalances seen on land/ocean.)
Global Water Reservoir
Reservoir
%age
Oceans
97.3
Polar ice,
glaciers
Groundwater
2.1
Lakes
0.01
Soil moisture
0.01
Water vapour
0.001
Rivers
0.0002
0.6
• Surface water seeps/percolates into ground 
soil moisture or Groundwater (GW)  Imp
source of freshwater (also rivers & lakes).
• GW beyond evaporation & reach of plant roots.
• Water table: Surface of GW.
• Aquifer: Porous underground structure,
composed of limestone/sand/gravel bounded by
impervious rock; largest GW source.
• Artesian well: Hydrostatic pressure forcing
water above ground as fountain.
Rain in the Mountains
Precipitation & Ecosystem Distribution
• Annual rainfall 0-25 cm  Desert
• 25-75 cm  Grassland
• >75 cm  Forest
• Can there be
“desert in the rain”?
Precipitation & Nutrients
• Surface runoff water imp in movement of
nutrients from one ecosystem to another.
• Which is more nutrient-rich:
upland or
lowland areas?
• High
productivity?
Climate & Treeline
• Treeline: Edge of the habitat at which trees
are capable of growing.
• Adverse
climatic
conditions
beyond
treeline.
Himalayan Treeline
• In the central Himalayan region, pine –
deodar treeline is found at 2800-3000 m &
snowline at 5000 m.
• Region in between (alpine zone): Herbs,
Shrubs, lichens, mosses.
• Migration of treeline upwards in Himalayas
due to global climate change.
Climate Classification
• Koeppen’s system most widely used.
• Relationship b/w latitude & temperature.
• - A  Tropical forests; hot all seasons; high
rain.
• - B  Dry climates
• - C  Warm dry summers, cool wet winters.
• - D  Cold forest climates; severe winters.
• - E  Polar climates.
Holdridge Life Zone Classification System, pp. 434
(TB)– Vegetation best expression of climate
Climograph
• Graph representing relation b/w temp &
rainfall.
• Helpful in weather prediction.
• Useful in introduction of species in new
areas.
• Example
of
lavender
Comparing Climographs
USA
USA
An Experience in Sangli, Maharashtra
• Drought-prone district (esp in 1980s).
• Past rainfall records  Enough rain  Improper
water management.
• Overdrawn water for water intensive crops
(sugarcane).
• Villagers + Activists + Technoloists  Mukti
Sangharsh
• 1.2 ha offered by a farmer for experiment: subabul
(0.3 ha), jowar (0.5), red gram (0.2), pomegranate &
ber (0.2).
• Success  Irrigation, leaf manure, employment.
• In years of better rain, additional water  onion.