HERATH H.M.L.K. SIHILELLA J.P.W.P. ABEYSINGHE D.C. DHANUSHIKA M.P. Wayamba University of Sri Lanka -- International Forestry and Environment Symposium 2011 Annual Symposium organized by Department of Forestry and Environmental Science, University of Sri Jayewardenepura, Nugegoda, Sri Lanka http://fesympo.sjp.ac.lk/

1. Trends in extreme events of rainfall
in low country wet zone of Sri Lanka
HERATH H.M.L.K.
SIHILELLA J.P.W.P.
ABEYSINGHE D.C.
DHANUSHIKA M.P. 1

2. 2

3. • Climate is changing
• Climate change affects both growth and the
production of plants
3

4. • Rubber and tea are main
revenue earners among
plantation crops in Sri Lanka
• Most of rubber plantation and
Low grown tea plantations;
Mainly confined in low country
wet zone region of the Island
4

5. • Both rubber and tea plantations have direct
relationships with the climate
• Require well spread-out rainfalls
Tea - 1000 to 1250mm
Rubber - 1650 to 3000mm
5

6. Changes in the 600
amount and the 500
Rainfall (mm)
400
distribution of 300
rainfall in Sri Lanka 200
100
are not very 0
May
Mar
Dec
Jan
Jun
Apr
Aug
Feb
Sep
Oct
Nov
Jul
apparent
6

7. Variability in climatic parameters: Variability
due climate change may overwhelmed by the
random variability
5000
4500
Rainfall (mm)
4000
3500
3000
2500
2000
1500
1945
1985
1940
1950
1955
1960
1965
1970
1975
1980
1990
1995
2000
2005
2010
Year
7

8. to identify trends in extreme events of rainfall
in low country wet zone of the Island
8

9. 9

10. Daily rainfall data
from 8 Agro
meteorological
stations for the
period of 1941-2010
were used
10

11. Agro ecological region, elevation, latitude and longitudes of
Agro meteorological stations under investigation
Agro- met AER Elevation (m) Latitude Longitude
station
Awissawella WL1 134 6057’11’’N 80013’6’’E
Dartonfield WL1 152 6031’0’’N 80010’0’’E
Ratnapura WL1 259 6058’N 80046’E
Ambanpitiya WL2 297 7014’0’’N 80020’0’’E
Galle WL3 105 7046’N 80017’E
Hanwella WL4 81 6054’23’’N 8005’23’’E
Kalutara WL4 15 6035’24’’N 79057’36’’E
Matara WL4 2 14041’3’’N 39024’52’’E
11

12. At each location,
• Annual, monthly and weekly rainfalls
• Number of rainy days
A rainy day is defined as a day receiving ≥0.5mm rainfall
• Wet spells
• Dry spells
12

13. • Extreme events were identified using the
boundary line technique
• Regression techniques to identify trends
13

14. Boundary Line Approach
Upper boundary
Lower boundary
14

15. 15

16.  Amount and the distribution of rainfall
Linear trend and the respective R2 values of total
annual rainfalls at each location
Location Trend R2 value
Ambanpitiya -10.43 0.155
Awissawella -3.99 0.023
Dartonfield -4.334 0.011
Galle -7.127 0.101
Hanwella -1.705 0.005
Kalutara -1.33 0.003
Matara -5.825 0.073
Ratnapura -3.166 0.017
16

17.  Trends of all the locations were not
significant
 But the signs of the trends were negative
 The temporal variations of daily rainfall
variability were random in all the locations
17

18. Ambanpitiya
4000 Linear (Ambanpitiya)
3500
Rainfall (mm)
3000
2500
2000
1500
1000
500
0
1941
1945
1949
1953
1957
1961
1965
1969
1973
1977
1981
1985
1989
1993
1997
2001
Year
Temporal variation of annual rainfall in Ambanpitiya
18

19. Boundary line analysis on annual rainfall
Trends and the R2 Location Trend R2
values for the Ambanpitiya -65.8 * 0.35
lower boundary Awissawella -29.2 0.07
Dartonfield -18.7 0.03
Galle -26.6 * 0.24
Hanwella -12.0 0.05
Kalutara 1.2 0.00
Matara -34.4* 0.17
Ratnapura 10.3 0.06
* Significant at p<0.05
19

20. 3000
Minimum Linear trend
2500
Rainfall (mm)
2000
1500
1000
500
0
1943
1948
1953
1958
1963
1968
1973
1978
1983
1988
1993
1998
2003
2008
year
Temporal variations of lower boundary of annual
rainfall in Ambanpitiya
20

21.  The temporal variation of maximum and
minimum occurrences of annual rainfalls
events in some locations were statistically
significant
 This is an indication of having some years
with comparatively low annual rainfalls
21

22.  Temporal variations in wet and dry days
Linear trend and the Location Trend R2
respective R2 values Ambanpitiya -1.026*** 0.54
of wet days at each Awissawella -0.611*** 0.22
location Dartonfield -0.211 0.05
Galle -0.327** 0.156
Hanwella -0.458** 0.142
Kalutara -0.524** 0.132
Matara -0.827*** 0.421
Ratnapura -0.004 0.001
** Significant at p<0.01, ***Significant at p<0.001
22

23. 250
200 Wet days Linear trend
No. of Wet days
150
100
50
0
1973
1977
1941
1945
1949
1953
1957
1961
1965
1969
1981
1985
1989
1993
1997
2001
2005
2009
Year
Temporal variation of annual wet days together with
its linear trend in Ambanpitiya
23

24.  Trends in lower and upper boundary of
annual wet days were statistically significant
24

25. 250
Upper boundary Linear trend
200
No. of wet days
150
100
50
0
1953
1943
1948
1958
1963
1968
1973
1978
1983
1988
1993
1998
2003
2008
Year
Upper boundary line the trend fitted to annual wet
days in Ambanpitiya
25

26. 160
140 Lower boundary Linear trend
120
No. of wet days
100
80
60
40
20
0
1943
1948
1953
1958
1963
1968
1973
1978
1983
1988
1993
1998
2003
2008
Year
lower boundary line the trend fitted to annual wet
days in Ambanpitiya
26

27.  significant decline in number of wet days
 A risk of aggregating heavy showers
27

28.  Temporal variation of maximum dry run
Linear trend and the Location Trend R2
respective R2 values Ambanpitiya 0.58** 0.35
of annual maximum Awissawella 0.36** 0.31
dry run in each Dartonfield -0.41 0.12
location Galle 0.08 0.01
Hanwella 0.38** 0.26
Kalutara 0.25 0.07
Matara 0.73** 0.40
Ratnapura 0.14* 0.13
* Significant at p<0.05, **Significant at p<0.01
28

29. 70 Max. dry run
Maximum dry run (days)
60 Linear trend
50
40
30
20
10
0
1961
1941
1945
1949
1953
1957
1965
1969
1973
1977
1981
1985
1989
1993
1997
2001
2005
2009
Year
Temporal variation of maximum dry run with its
linear trend in Ambanpitiya
29

30.  Risk of having lengthy dry spells in some
locations in the Low country wet zone
30

31.  No significant change in annual rainfall
(Cumulative rainfall)
 Significant tendency of having incidences of
aggregated heavy showers in the low
country wet zone
 Signs of lengthy dry spells
31

32.  Adverse impacts on some operations like
crop establishment and fertilizer application
 Favorable for latex exploitation
32

33. • Director of the Rubber Research Institute of Sri Lanka
(RRISL)
• Dr. (Mrs.) Wasana Wijesekara, Head of the Biometry
Section of RRISL
• Mr. Vidura Abeywardena, technical officer of the
Biometry Section of RRISL
• Department of Meteorology
33

34. 34