Errors arise in climate data due to instrument
error, observation errors and transcription errors. Such errors can
unduly influence climate analysis particularly for climate change. Therefore
we need to assess the quality of the data. Such procedures are useful
to infill missing data.
Climate analyses is sensitive to
outliers arising from a variety of sources, like shifting of the stations,
instrumental errors and human error. Hence, prior to analysis it is important
to remove outliers.
Temperature fields should show spatial
uniformity. An anomalous rise in one station is likely to be associated
with a similar rise in neighbouring stations. Therefore we may compute
the standard error for each year for the anomalies for each station to
assess the degree of scatter in a given year for stations across the country
as a measure of quality.
Such quality analysis gives a way
to build homogeneous and complete data set and reconstruct the discarded
or missing data.
The precision of
climate change estimates from instrumental data is sensitive to the quality
of data. The quality of the monthly temperature and rainfall data at the
main stations of the Sri Lanka Department of Meteorology and Agriculture
were evaluated based on station histories, comparison with observations
at neighbouring stations and internal consistency of the data. The Global
Historical Climatology Network (GHCN) has previously carried out such
quality control for 11 Sri Lankan stations. We have undertaken quality
assessment for 18 stations each of which had a longer duration than used
in the GHCN analysis and had fewer missing records. The GHCN quality checks
lead to all data prior to 1950 from Trincomalee, Batticaloa and Colombo
and data from Hambantota prior to 1921 being discarded. The present quality
control leads to a much smaller set of data being discarded.
Inter Annual variations – Temperature at any station should relate
to that in neighbouring stations. We may use a statistical techniques
to estimate the temperature at station using the observations at neighbouring
stations alone. The comparison of such reconstruction and observation
is illuminating.
| ...::
Conference Proceedings |
Dec 1999:
with Gunaratne, A.U.K, A mass consistent wind model for Sri Lanka, Proceedings
of the 8th Asian Fluid Dynamics Congress, Shenzen, China 8:817-820.
Dec 2002: with Heli Bulathsinhala, Quality Evaluation
of Mean Historical Temperature Data in Sri Lanka, Sri Lanka Association
for the Advancement of Science, 58th Annual Sessions, University of
Colombo, Colombo, Sri Lanka
| ...::
Abstracts submitted |
Nov 2004,
Climate change assessment for Sri Lanka from quality evaluated data. International
conference on sustainable water resources management in the changing environment.
July 2004, Topographically informed interpolation of
temperature in Sri Lanka. Submitted to: First national symposium on Geo-Informatics,
PGIA, Sri Lanka. |
Given
its size, Sri Lanka shows a remarkable variation of climate among its
regions. The variation in temperature is modest with the mean value being
27oC with a mean daily range of 6oC. The relative humidity varies from
60% to 90%. Westerly winds prevail over the island from May to September
and North-Easterly winds prevail from December till February. Rainfall
measurements are available for Colombo from 1853 and there are a dozen
stations which have a 130 year rainfall record and over 500 rainfall recording
stations with a 50 year record. Some of these stations are shown in the
figure below along with the topography
Sri Lanka has been regionalized considering
-
....*
annual rainfall (as wet, dry and intermediate),
....* elevation (as up, mid and low country)
and based on
....* agro- ecological zones (considering
rainfall, elevation .......and soils).
Puvaneswaram and Smithson of University of Sheffield, UK. presented a
scheme that considers seasonal rainfall tables (see map) It is useful
as different climatic mechanisms dominate specific regions.
| ..:: Monthly
Regional Rainfall |
Rainfall is high from October
to December and from April to June through all regions of the island.
During the intervening periods, rainfall is augmented on the western hill
slopes from May to September and on the eastern hill slopes from December
till February.
There is no clear cut method of specifying
seasons for Sri Lanka. Traditional agricultural seasons are from -
....*
October to March (Maha)
....*
April to September (Yala).
....*
Meteorologists have demarcated the
seasons as the
....*
North-East monsoon (DJF)
....*
First Inter-Monsoon (MA)
....*
South-West monsoon (MJJAS) and
....*
Second Inter-Monsoon (ON)
The significant climatic
processes that bring rainfall are the passage of the Tropical Convection
Zone (TCZ) around April and November, orographic rainfall in the Western
hill slopes (MJJAS) and in the Eastern hill slopes (DJF) and cyclonic
storms particularly in November and December. The monsoon over the region
modulates the rainfall particularly in the boreal winter (DJF) and summer
(JJA).
Meteorological demarcation is useful for studies of wind and temperature
patterns but does not separate modes of rainfall well. For analysis of
rainfall, we often use a breakup of the agricultural seasons into their
wetter early half (AMJ and OND) and drier later halves (JAS and JFM).
|
- November 2005: Manjula
Siriwardhana, Janaki Chandimala, Siraj Razick, Upamala Tennakoon and Lareef Zubair, FECT Technical Report -7, 2005, Quality evaluation
of diurnal temperature range in Sri Lanka.
|
- November
2005: Manjula Siriwardhana, Heli Bulathsinhala, Kusalika Ariyarathna,
Irugal Bandara, Janaki Chandimala, Siraj Razick, Upamala Tennakoon and Lareef Zubair, FECT
|
- Technical Report-3, 2004,
Quality Evaluation of Historical Rainfall Data in Sri Lanka.
|
-
May
2005: Manjula Siriwardhana, Kusalika Ariyarathne, Irugal
Bandara, Heli Bulathsinhala, Janaki Chandimala, Siraj Razick, Upamala
Tennakoon and Lareef Zubair, FECT Technical Report-2,
Quality evaluation of historical maximum and minimum temperature data
in Sri Lanka.
|
- February,
2005, Current Climate and Climate Change Assessments for Coconut
and Tea Plantations in Sri Lanka. Submitted to: START, Washington, D.C.,
USA,
- December 2004: Heli
Bulathsinhala, Manjula Siriwardhana, Kusalika Ariyarathne, Irugal Bandara,
Janaki Chandimala, Siraj Razick, Upamala Tennakoon and
Lareef Zubair, FECT
|
-
December
2004: Irugal Bandara, Kusalika Ariyarathne, Janaki Chandimala,
Siraj Razick, Manjula Siriwardhana, Upamala Tennakoon
and Lareef Zubair, FECT Technical Report-4, Quality evaluation of
historical maximum and minimum temperature data in the agro-meteorological
stations in Sri Lanka.
- Technical Report-1, 2004,
Quality evaluation of historical mean temperature data in Sri Lanka.
|
