There the rise in the minimum temperature is

There is evidence to suggest that
the urbanization and land use change the mean surface air temperature. An
assessment of urbanization effects on surface air temperature based on a set of
rural station data carried out by Jones et. al. (1990)
reveals that urbanization is at least an order of magnitude less than the warming
of  0.5 °C seen over land areas on a century scale. Recent studies carried
out in large cities report much higher values (Fujibe
2011; Jeganathan and Andimuthu 2013). Although it is difficult to separate
changes due to natural climate variability from those due to the increase in
greenhouse gases in the atmosphere, existing evidence suggest that the diurnal
temperature range is decreasing in many regions of the world (Karl et. al. 1993). The DTR is defined as the difference
between the mean monthly maximum and minimum temperatures. Karl et. al. (1993) reports that the rise in the minimum
temperature is in the order of three times that of the maximum temperature (0.84
°C compared to 0.28 °C) which is
approximately equal to the increase in the mean temperature during the period
1951 – 1990. Easterling et al. (1997)
and Jones et al. (1999) also reported a decrease in DTR over many
parts of the world. The DTR is generally consider as an important proxy for
climate change.

 

There is also a growing concern that climate change will adversely affect
the mountainous regions of the world (Diaz and
Brandley 1997). Change in climate can have a impact on the ecology and
implications for animals and plant species living in higher elevation areas (Schneider 1990). The published literature show
that temperatures in high elevation mountain areas have increased by 1-2 °C during the last century with the cold temperatures rising faster than
the warm temperatures (Weber et. al. 1997; Beniston
et. al. 1997). A study carried out by Diaz and Graham (1997) on decadal changes in temperature in the
tropical regions concludes that there are regional differences in temperature
trends, both spatially, and with respect to elevation in the middle
latitudes. 

 

In relation to Sri Lanka which is in the tropics, an analysis carried
out with a long term annual mean air temperature time series revealed significant
warming trends in all regions (Chandrapala 1996).
Statistically significant warming trends between 0.08 °C and 0.25 °C per decade
were reported for annual temperature records from 1961 to 1990. A study carried
out to find the impact of climate change on the selected areas of the hill
country reported a significant rise in the annual temperature series during the
last hundred years (Bandara and Wickremagamage
2004). The observed trend has been steeper during the latter half of the
last century. A study carried out to find the effect of deforestation on the plantation
areas in the central highlands indicates that the increasing trend is confined
to the higher elevation areas. However, due to meteorological observations
starting long after a large area of the forest was cleared for coffee
plantation, it was not possible to isolate the cause of the temperature rise in
the hill country (Wickremagamage 1998).

 

To our knowledge, information on the variation of DTR
over Sri Lanka is almost non-existent. Thus, the objective of the present study
is to investigate trends in DTR, the minimum temperature and the maximum
temperature in Nuwara Eliya on annual, seasonal and monthly time scales where
the highest warming trends were observed.