trends in extreme events of rainfall in low country wet zone of sri lanka
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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/TRANSCRIPT
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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.
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Introduction
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• Climate is changing
• Climate change affects both growth and the production of plants
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• 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
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• Both rubber and tea plantations have direct relationships with the climate
• Require well spread-out rainfalls Tea - 1000 to 1250mm
Rubber - 1650 to 3000mm
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Changes in the amount and the distribution of rainfall in Sri Lanka are not very apparent Jan Fe
bMar Apr
May Jun JulAug
Sep
Oct NovDec
0
100
200
300
400
500
600
Rain
fall
(mm
)
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Variability in climatic parameters: Variability due climate change may overwhelmed by the random variability
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
15002000250030003500400045005000
Year
Rain
fall
(mm
)
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Objective
to identify trends in extreme events of rainfall in low country wet zone of the Island
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Materials and Methods
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Daily rainfall data from 8 Agro meteorological stations for the period of 1941-2010 were used
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Agro ecological region, elevation, latitude and longitudes of Agro meteorological stations under investigation
Agro- met station
AER Elevation (m) Latitude Longitude
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
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At each location,
• Annual, monthly and weekly rainfalls
• Number of rainy daysA rainy day is defined as a day receiving ≥0.5mm rainfall
• Wet spells
• Dry spells 12
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• Extreme events were identified using the boundary line technique
• Regression techniques to identify trends
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Boundary Line Approach
Upper boundary
Lower boundary
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Results and Discussion
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Amount and the distribution of rainfall Linear trend and the respective R2 values of total
annual rainfalls at each location
Location Trend R2 valueAmbanpitiya -10.43 0.155Awissawella -3.99 0.023Dartonfield -4.334 0.011Galle -7.127 0.101Hanwella -1.705 0.005Kalutara -1.33 0.003Matara -5.825 0.073Ratnapura -3.166 0.017
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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
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Temporal variation of annual rainfall in Ambanpitiya
19411946
19511956
19611966
19711976
19811986
19911996
20012006
0500
1000150020002500300035004000
Ambanpitiya
Linear (Ambanpitiya)
Year
Rain
fall
(mm
)
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Location Trend R2
Ambanpitiya -65.8 * 0.35
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
Boundary line analysis on annual rainfall
Trends and the R2 values for the lower boundary
* Significant at p<0.05
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Temporal variations of lower boundary of annual rainfall in Ambanpitiya
1943
1948
1953
1958
1963
1968
1973
1978
1983
1988
1993
1998
2003
2008
0
500
1000
1500
2000
2500
3000
Minimum Linear trend
year
Rain
fall
(mm
)
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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
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Temporal variations in wet and dry days
Location Trend R2
Ambanpitiya -1.026*** 0.54Awissawella -0.611*** 0.22Dartonfield -0.211 0.05Galle -0.327** 0.156Hanwella -0.458** 0.142Kalutara -0.524** 0.132Matara -0.827*** 0.421Ratnapura -0.004 0.001
** Significant at p<0.01, ***Significant at p<0.001
Linear trend and the respective R2 values of wet days at each location
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19411945
19491953
19571961
19651969
19731977
19811985
19891993
19972001
20052009
0
50
100
150
200
250
Wet days Linear trend
Year
No.
of W
et d
ays
Temporal variation of annual wet days together with its linear trend in Ambanpitiya
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Trends in lower and upper boundary of annual wet days were statistically significant
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Upper boundary line the trend fitted to annual wet days in Ambanpitiya
1943
1948
1953
1958
1963
1968
1973
1978
1983
1988
1993
1998
2003
2008
0
50
100
150
200
250Upper boundary Linear trend
Year
No.
of w
et d
ays
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lower boundary line the trend fitted to annual wet days in Ambanpitiya
1943
1948
1953
1958
1963
1968
1973
1978
1983
1988
1993
1998
2003
2008
020406080
100120140160
Lower boundary Linear trend
Year
No.
of w
et d
ays
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significant decline in number of wet days
A risk of aggregating heavy showers
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Temporal variation of maximum dry run
Location Trend R2
Ambanpitiya 0.58** 0.35Awissawella 0.36** 0.31Dartonfield -0.41 0.12Galle 0.08 0.01Hanwella 0.38** 0.26Kalutara 0.25 0.07Matara 0.73** 0.40Ratnapura 0.14* 0.13
* Significant at p<0.05, **Significant at p<0.01
Linear trend and the respective R2 values of annual maximum dry run in each location
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1941
1945
1949
1953
1957
1961
1965
1969
1973
1977
1981
1985
1989
1993
1997
2001
2005
2009
010203040506070 Max. dry run
Linear trend
Year
Max
imum
dry
run
(day
s)
Temporal variation of maximum dry run with its linear trend in Ambanpitiya
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Risk of having lengthy dry spells in some locations in the Low country wet zone
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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
Conclusions
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Adverse impacts on some operations like crop establishment and fertilizer application
Favorable for latex exploitation
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Acknowledgements• 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
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THANK YOU