Title of the Study: A Comparative Study of the Ambient Air Temperature Trends

at Anuradhapura and Maha Iluppallama

Investigator(s): T. K. Fernando and B.R.S.B. Basnayake

Scientific background and scope/objectives of the study:

Over recent years the concentration of greenhouse gases in the atmosphere has been increasing. Scientists are now convinced that human activity, such as the burning of fossil fuels, is responsible for the build up. This unnatural or forced increase in greenhouse gases results in the enhanced greenhouse effect.

More than 100 years of temperature and rainfall data at 14 meteorological stations including Anuradhapura (but not Maha Iluppallama), were analyzed for trends and rates of variation by Fernando and Chandrapala (1992). These analyses indicated that the annual mean air temperature, particularly over the period 1961-1990, has been increasing at all the 14 stations, by varying amounts.

The objective of this study was to compare the rates of variation (if any), of the mean minimum, mean maximum and mean air temperatures at Anuradhapura and Maha Iluppallama and investigate whether these variations (if any) are due to enhanced greenhouse effect or urbanization or both.

These two places were chosen for the following reasons:

a). the proximity of the two places (the distance is about 27 km, as the crow flies);

b). Maha Iluppallama is semi-urban / rural area compared to Anuradhapura which is a city that has undergone urbanization over the last 20-30 years;

c). the existence of two meteorological stations, one located at Anuradhapura and the other at Maha Iluppallama, and the availability of temperature data over a long period of time.

The meteorological office at Anuradhapura is located in the heart of the city, whereas that at Maha Iluppallama is located within the premises of the Field Crop Research and Development Institute, belonging to the Department of Agriculture, in a much more rural setting. Urbanization effects at Maha Iluppallama could be considered to be minimal compared to those at Anuradhapura.

Experimental Method:

The meteorological office at Maha Iluppallama was started in November 1952, whereas that at Anuradhapura was started much earlier, in 1870. Since this is a comparative study, the period used was 1953-2000. Temperature data for the months of January, April, July and October were analysed for possible trends by filtering the time series using the Gaussian low pass filter with nine weights, 0.01, 0.05, 0.12, 0.20, 0.24, 0.20, 0.12, 0.05 and 0.01. Mathematically the filter is represented by the equation,

where X_t is the filtered value of the series corresponding to the t^th term thereof, and w_I is the weight by which the value of the series i units removed from t is multiplied.

The different time series were then subjected to linear regression analyses to quantify the trends, if any.

Results Obtained:

1. Trend Analyses: Trend analyses indicate that the mean minimum, mean maximum and mean air temperatures have been increasing both at Anuradhapura and Maha Iluppallama, except for the mean maximum air temperature at Maha Iluppallama in July and October, where very insignificant decreases are indicated.

2. Linear Regression Analyses: Linear regression analyses indicated that the rates of increase of air temperature at Anuradhapura for all the series are gigher than those at Maha Iluppallama, with the exception of the mean minimum air temperature series for July. The following table gives the highest and the lowest rates of increase at Anuradhapura and Maha Iluppallama.

Rates of increase in air temperature (deg. C/year)

Anuradhapura – Mean Minimum Maha Iluppallama – Mean Minimum

	Amount	Month	R^2		Amount	Month	R^2
Highest	0.0281	April	0.652	Highest	0.0262	April	0.491
Lowest	0.0113	January	0.080	Lowest	0.0026	January	0.004

Anuradhapura – Mean Maximum Maha Iluppallama – Mean Minimum

	Amount	Month	R^2		Amount	Month	R^2
Highest	0.0575	January	0.860	Highest	0.0212	April	0.511
Lowest	0.0129	July	0.309	Lowest	0.0159	January	0.303

Anuradhapura – Mean Maha Iluppallama – Mean Minimum

	Amount	Month	R^2		Amount	Month	R^2
Highest	0.0338	January	0.617	Highest	0.0251	April	0.566
Lowest	0.0158	July	0.539	Lowest	0.009	October	0.199

Conclusions:

Taking into account the location of the meteorological station at Maha Iluppallama and the fact that both mean minimum air temperatures and mean maximum air temperatures at this station have been increasing, it is likely that these increases are due to enhanced greenhouse effect than to urbanization effects.

The fact that the rates of increase of all the temperature series at Anuradhapura (except for the mean minimum temperature series for July) are higher than those at Maha Iluppallama, and the fact that, at Anuradhapura, the rates of increase of mean maximum air temperature are, in general, greater than the rates of increase of mean minimum air temperature, suggest that these increases are due probably to both the enhanced greenhouse effect and urbanization.

Home