Mavis Toh, Straits Times 7 Jun 09;
Burnt out by the sweltering heat?
Last month, temperatures here hit a scorching 33.6 deg C, and it seems the heat is not likely to let up any time soon.
May is the second hottest month of the year in Singapore, following behind June, said the National Environment Agency's (NEA) Meteorological Services Division.
The average temperature last month was 28.7 deg C, up from 28.5 deg C in April and 27.2 deg C in March. The hottest day in May was recorded in 2005, when the mercury hit 35.4 deg C, just shy of the 36.0 deg C on March 26, 1998 - Singapore's hottest day ever.
The NEA said that the warmer weather in May and June can be attributed to light winds and the strong sun.
Associate Professor Matthias Roth of the geography department at the National University of Singapore explained that the hot weather results from the sun being directly overhead at the end of March.
'Temperature usually lags a little behind the sun,' he said. 'We also had a lot of clear days last month with no clouds to absorb the radiation and so we got the full impact of the sun.'
The low rainfall and light winds this month will also do little to relieve the heat.
Whenever May comes, sweaty Singaporeans are quick to point their fingers accusingly at the sun. But often, what's making them sticky and uncomfortable is the humidity.
Humidity can be explained as the amount of water vapour in the air, or the cause of the 'sticky feeling' one experiences on hot days.
When the humidity is high, sweat does not evaporate as quickly and hence 'we feel much hotter than the actual temperature', said an NEA spokesman.
In contrast, when the humidity level is low, sweat evaporates quickly, resulting in a cooling effect.
Dr Roth pointed out that this explains why 32 deg C in Singapore can feel much hotter than the same temperature in France, for example, due to the difference in humidity level.
'Humidity affects man's perception of comfort,' he said. 'The higher the humidity, the less comfortable we feel.'
Singapore's location near the equator explains its high humidity.
Nanyang Technological University Assistant Professor Koh Tieh Yong of the School of Physical and Mathematical Sciences said that the noon sun is high in the sky all year round because Singapore lies in the equatorial tropics. The higher temperature in the equatorial tropics encourages evaporation. This causes much evaporation from the surrounding seas, loading the atmosphere with plenty of water vapour.
The average relative humidity last month was 83 per cent, up from 79.1 per cent the same time last year. Humidity level is affected by air temperature and hence some months are more humid than others.
Although the high humidity prevents sweat from evaporating and may even cause heatstroke, it is not all bad. It also prevents people from suffering very dry skin and cracked lips, which are common occurrences in places with low humidity.
Singaporeans can expect cooler days come September, but experts say temperatures will increase in the long run. Man's continual production of greenhouse gases means global warming which, in turn, means the world's average temperature will increase gradually over decades and centuries.
Prof Koh said that in one scenario of projected greenhouse gases increase where no mitigation policies beyond the current ones are put in place, the 10-year global average surface temperature is estimated to increase by 1.8 deg C in the 2090-2099 period compared with the 1990-1999 period.
Dr Roth said: 'The solution must be a global effort, not a local one.'
