This is the 9th lesson of the course 'Poverty and Environment ' taught at the Faculty of Social Sciences and Humanities, Rajarata University of Sri Lanka

1. Lesson 9:
Climate and Soils of Sri Lanka
P.B. Dharmasena
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dharmasenapb@ymail.com , dharmasenapb@gmail.com
https://independent.academia.edu/PunchiBandageDharmasena
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ibutions http://www.slideshare.net/DharmasenaPb
Poverty and Environment
Course code: ECON/EMGT 4214
Friday from 8.30-11.30 a.m

2. Three topographic zones:
• The central
highlands (South-
central part; 750-
2500 m)
• The plains (125-
750 m),
• The coastal belt (0-
125m)
• Sixteen principal rivers
(longer than 100 km)
• 12 rivers carry about
75 % of the mean river
discharge of the
country
• The longest river:
Mahaweli Ganga (335
km).

3. Weather vs. Climate
Weather and
Climate are not
the same
• Weather - The
conditions of the
atmosphere at a
particular place
and time.
• Climate -
Average
conditions of a
certain place over
a long period of
time

4. Climatic Seasons in Sri Lanka
• First Inter-Monsoon (FIM) –
March & April
• Southwest Monsoon (SWM)-
May – September
• Second Inter-Monsoon (SIM)-
October & November
• Northeast Monsoon (NEM) –
December - February

5. Climatic zones of Sri Lanka
Rainfall
below 1,750 mm - Dry zone
1,750 - 2,500 mm - Inter mediate zone
above 2,500 mm - Wet zone

6. Agro-Ecological Zones of Sri Lanka
• 24 agro-ecological
zones (RF &
Altitude), combined
with effects of soil,
land form and land
use (agricultural
activities)
• 49 sub-zones
– WZ – 16
– IZ – 20
– DZ - 13
DRYZONEINTERMEDIATEZONEWETZONE

7. Sub zoning
• Each AER is denoted by a 4-character code consisting of letters and a
number; (eg:.DL1a)
– Three major rainfall zones are indicated by the first upper case letter of
the code (W, I and D);
– Three categories of elevation are noted by the second upper case letter
of the code (L, M and U);
– The numerical character in the third place of the code represents the
degree of wetness on the scale of 1  5 where 1 represents the most
favorable
– The lower case letter in the fourth place indicates a sub-region as
determined by rainfall and other physical environmental factors. The
degree of wetness decreases from a  f .

8. WL1a
WL1b
WL2a
WL2b
WL3
WM1a
WM1b
WM2a
WM2b
WM3a
WM3b
WU1
WU2a
WU2b
WU3

9. IL1a
IL1b
IL1c
IL2
IL3
IM1a
IM1b
IM1c
IM2a
IM2b
IM3a
IM3b
IM3c
IU1
IU2
IU3a
IU3b
IU3c
IU3d
IU3e

10. 0
50
100
150
200
250
300
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
DRFmm
Month
Monthly rainfall distribution in IL 2 region
AnnualDependableRainfall = 1,600mm

11. DL1a
DL1b
DL1c
DL1d
DL1e
DL1f
DL2&DL3
DL2a
DL2b
DL3
DL3&DL4
DL4
DL5

12. 0
50
100
150
200
250
300
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
DependableRainfall(mm)
Month
Monthly rainfall in DL 2b region
Annual DRF =1100 mm

13. 0
50
100
150
200
250
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Rainfallinmm
Month
Monthly rainfall distribution in DL1b AE region
Annual DRF = 900 mm

16. Soil Type Extent (‘000
ha)
%
Reddish Brown Earths (RBE) 1,610 24.6
Low Humic Gley (LHG) 950 14.5
Non Calcic Brown (NCB) 163 2.5
Red and Yellow Latasols (RYL) 320 4.9
Immature Brown Loams (IBL) 205 3.1
Solodized Solonetz 210 3.2
Grumusols 15 0.2
Red Yellow Podzolic (RYP) 1,490 22.8
Reddish Brown Latasol (RBL) 60 0.9
Alluvials 450 6.9
Regosols 190 2.9
Bog and Half Bog 60 0.9
Lithosols 210 3.2

17. General crops for some soils in Sri Lanka
1. Reddish Brown Earth – Maize / Grain legumes
2. Low Humic Gley – Paddy
3. Red-Yellow Podzolic – Plantation crops
4. Non Calcic Brown – Big onion / Red onion
5. Red Yellow Latasols – Cashew
6. Sandy Regosols – Coconut
7. Alluvial – Paddy
8. Grumusols – Paddy
9. Immature Brown Loam – Home garden

18. RBE (Rhodustalfs)
 Largest extent of the land in the dry zone
 Characteristic reddish brown colour
 Series: Medawachchiya, Aluthwewa, Anamaduwa,
Ranorawa, Thadarathu, Siyambalanduwa, Ranna,
Nonagama, Kotawehera mankada, Walawe, Ulhitiya
 Soil catenary sequence
Well Drained Imperfectly Drained Poorly Drained
RBE
LHG

19. Characteristics of RBE Soils
Physical Properties
Soil Depth - Moderate (60 cm – 150 cm)
Texture - Sandy clay loam
Structure - Strong sub angular blocky
Infiltration - 3 – 9 cm in 4 hours
Available Moisture 130 – 170 mm/m
Consistency - Hard when dry
Slightly friable when moist
Very sticky when wet

20. RBE (Rhodustalfs)

21. Low Humic Gley Soils (Tropaqualfs)
 Third most extensive soil group in Sri Lanka
 Located at the foot slopes of the undulating landscape
 Characterized by the wetness or gleying through the
profile
 Availability of calcite concretions
Physical Properties
Texture - Sandy clay to clay
Structure - Sub angular blocky to massive
WHC - Fairly good

22. Low Humic Gley Soils (Tropaqualfs)

23. Red – Yellow Podzolic soils (Tropudult)
 Second most extensive soil group in Sri Lanka
 Modal soil of the wet zone of Sri Lanka
 Mostly known as Lateritic soils
 Majority found in the hilly part of the country
 Colour varies from strong brown to yellowish brown
 Series: Minuwangoda, Galigamuwa, Pallegoda,
Homagama, Boralu, Agalawatta, Dodangoda, malaboda,
Mattakele, Horton, Nuwara Eliya, Maskeliya, Weddagala

24. Red – Yellow Podzolic soils
• Deeply developed soil
profile
• Higher structural stability
and better response to
management
• Moderate CEC
• Low pH
• Prone to erosion due to
steep topography (in the mid
and up country)

27. The Climate
Climate is the average of weather over
time.
Climate tells us what weather is usually like in a
given place.
How would you describe the climate where you
live?

28. What is climate variability ?
“Climate variability” refers to changes in
climate from one year to another.
It can be caused by changes in ocean
conditions far away, which can affect climate
all over the world (for ex: el Niño)
Climate variability is natural and occurs on a
regular basis.

29. What is climate change ?
Climate change is the change in
climate over a time period from 10
to 100s of years.
Climate change involves both
natural changes and changes
caused by people.

30. Why does our climate change?
• Over the history of the
Planet, the climate has
changed naturally. It
happened during the ice
ages, and maybe also
when the dinosaurs
disappeared.
• In addition, human
activities have warmed
the climate.

31. Main Natural Factors
that Affect Climate

32. The Sun
• The amount of energy
coming off the Sun is not
constant but keeps changing
• Slow changes in the Earth's
distance from the Sun affect
the amount of energy
received from the Sun.
• Those variations are believed
to be one of the causes that
start ice ages.
Main Natural Factors

33. • Volcanoes - when a volcano
erupts it throws out large
amounts of sulphur dioxide
(SO2), water vapour, dust, and
ash into the atmosphere.
• The climate system is made up
of many components that all
affect climate: this includes
ocean currents, atmospheric
circulation, sea ice and land
covers (trees, grass…)
Main Natural Factors

34. The Greenhouse Effect controls our climate
• When energy from the Sun enters the
Earth's atmosphere, about a third of it is
reflected back to space.
• Of the remainder, most is absorbed by the
Earth’s surface. Some also stays in the
atmosphere, absorbed by water vapor and
green house gases.
• This natural Greenhouse Effect is vital to
life as we know it.
Right now, the average temperature on
the Earth is 15°C. If there was no
greenhouse effect, the average
temperature would be -18°C (33°C colder
than it is now – too cold for most living
beings).
3 is the Greenhouse Effect

35. Main Human
Factors that
Affect Climate

36. Greenhouse Gases
• Human activities send gases (for example methane,
carbon dioxine CO2) into the athmosphere that enhance
the greenhouse effect.
• Many of the gases come from fossil fuels such as oil,
coal and natural gas to run vehicles, and generate
electricity for industries or households.
• When the atmosphere contains too much of those
gases, the whole atmosphere and the Earth becomes
hotter, like it does in a greenhouse. The atmosphere
holds on to too much heat, instead of letting it escape
into space.
Main Human Factors
This causes global warming !

37. The example of CO2
• Today there is about 25% more Carbon dioxide
(CO2) in the atmosphere than in 1860. CO2 is the
greenhouse gas that people make the most of.
The more CO2 we put into the air, the more the
temperature could rise.
• Two of the biggest sources of CO2 are burning
fossil fuels and cutting down and burning trees.
• Forests are called ‘carbon sinks’ because they
take CO2 from the air and store it. When trees are
cut down and burned, the CO2 that is stored in
them is released back into the air. Scientists
believe that every year, 2 to 5 billion tonnes of
CO2 are released into the air from forests being
cut down and burned.
Main Human Factors

38. Aerosols
• Aerosols are tiny solid
particles or liquid droplets
that remain suspended in
the atmosphere for a long
time.
Main Human Factors
•They originate naturally (for example from volcanoes) but
also as a result of human activities (industries…). In the later
case, aerosols are considered pollutants, which cause direct
effects on the Earth’s radiation budget and also indirectly
through changing the formation and behavior of clouds.

39. Land Use Change
• There are over 6 billion people
on Earth. Humans continue
replacing forests and natural
vegetation with agricultural
lands. More and more people
move into cities, therefore
more houses are built. All this
has an impact on climate.
• For example, it affects the
evaporation of water and
therefore the rain cycle.
Main Human Factors

40. What is global warming?
It refers to an average increase in the
Earth's temperature, which in turn
causes changes in climate.
A warmer Earth leads to a wide range
of impacts on plants, wildlife, and
humans.
Observed data indicate that global
temperature over land and ocean has
increased by approximately 0.6°C
(1.08°F) since the late nineteenth
century.
Do you know exemples of effects
global warming has on our Planet?

41. Our future climate according to scientists
According to meteorologists and
climatologists (they are the scientists who
study weather and climate), the changing
climate very likely entail more:
•Heat waves
•Heavy rain and snow
•Droughts
•Tropical cyclones

42. Our future climate according to scientists
Rising sea level
Scientists also predict that global warming
will cause the level of water in the oceans
to rise between 15 and 95 cm in the next
100 years, because warmer temperature
will cause sea ice and glaciers to melt,
adding more water to oceans, and because
as water gets warmer, it takes up more
space

43. Climate Change
• Sri Lanka was ranked
second in a report
that considers
countries most
affected by Climate
change in the year
2017 as per the
Global Climate Risk
Index 2019. The
2019 Global Climate
Risk Index was
presented at the
United Nations
Environment summit
in Poland.

44. Climate Change
• As per the Index,
Puerto Rico (An
island belongs to
Caribbean
Islands) is the
worst affected by
climate changes
while the
Dominican
Republic holds
the third place on
the report.

46. Climate Change
• As per the report, a
total of 76 deaths that
occurred in Sri Lanka
during 2017 have
been directly
attributed to climate
change. The report
shows that the
monsoon rains which
cause floods and
landslides contribute
largely to this number.
The number of
displaced persons are
estimated to be
around 600,000.

47. Climate Change
• The report states
that around 20,000
people in the
Ratnapura district
alone have been
displaced owing to
adverse weather.

48. What is climate change?

49. Season Coefficient of Variation of
all Sri Lanka Rainfall
1931– 1960 1961 - 1990
Northeast Monsoon (Dec. to
Feb.)
31% 42%
First Intermonsoon (Mar. to
Apr.)
23% 27%
Southwest Monsoon (May.
to Sep.)
21% 16%
Second Intermonsoon (Oct.
to Nov)
22% 23%
Annual (Jan. to Dec.) 12% 14%
The Coefficient of Variation of all-Sri Lanka Rainfall during
the periods 1931-1960 and 1961-1990,