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THE National Environment Agency (NEA) had said last year that its data showed no significant annual rainfall trend in Singapore.
But an expert panel appointed by the Government to tackle the flooding problem said last week that Singapore had become wetter by 30 per cent in the past four decades.
Who is right?
The NEA told The Straits Times this week that it had reached a different conclusion because it used a different set of data.
It had said after the floods of last June that its conclusion was based on data from a single weather station in Changi.
The panel, on the other hand, drew on the NEA's data from a network of stations islandwide.
Panel member Lui Pao Chuen said that mass of data indicated that annual rainfall here went up by an average rate of 15mm a year between 1968 and 2008.
The panel also found that storms here had become more intense in the last 30 years, based on a study done by the NEA after the 2010 floods in Orchard Road. The agency had used data from 28 stations across the country.
Based on the trends, the expert panel has called on PUB to review the way it plans the drainage system here to cope with the bigger downpours.
Though the NEA's practice of using only one station as a reference point sounds counter-intuitive, it is technically in line with the method used by the World Meteorological Organisation (WMO).
The WMO's guidelines state that a 'reference station' - meant to monitor climate and detect changes at a national level - must have at least 30 years of rainfall and temperature data and be sited away from urban centres.
For the NEA, the Changi station is that reference station, and it said the rainfall trends there have reflected those at other stations across the island.
It said the Changi station has shown that more rain has fallen, but the increase has not been statistically significant.
But it conceded that half its weather stations across the island had logged higher, 'significant' increases in rainfall, including the stations in the central catchment area of MacRitchie and Paya Lebar; however, the stations near Orchard Road and Bukit Timah, which were hit by floods in recent years, had recorded no significant increases.
The agency is standing its ground on using the Changi station as its reference point, saying the method, and not using rainfall figures for the whole island as the panel did, fits WMO guidelines.
However, it said it would start putting on its website rainfall data from the various points across the island.
Climate scientists said the NEA should clarify what it considers a 'significant increase' in the amount of rainfall.
Assistant Professor Koh Tieh Yong at the Earth Observatory of Singapore said this would make clear if other groups such as the panel are evaluating the data using other standards.
Prof Koh recommended that the agency use at least some other stations that fit the WMO guidelines for reference stations to track rainfall trends across the island.
'If you want to know about rainfall over the island itself, then certainly you would welcome as much data as possible,' he said.
But an expert panel appointed by the Government to tackle the flooding problem said last week that Singapore had become wetter by 30 per cent in the past four decades.
Who is right?
The NEA told The Straits Times this week that it had reached a different conclusion because it used a different set of data.
It had said after the floods of last June that its conclusion was based on data from a single weather station in Changi.
The panel, on the other hand, drew on the NEA's data from a network of stations islandwide.
Panel member Lui Pao Chuen said that mass of data indicated that annual rainfall here went up by an average rate of 15mm a year between 1968 and 2008.
The panel also found that storms here had become more intense in the last 30 years, based on a study done by the NEA after the 2010 floods in Orchard Road. The agency had used data from 28 stations across the country.
Based on the trends, the expert panel has called on PUB to review the way it plans the drainage system here to cope with the bigger downpours.
Though the NEA's practice of using only one station as a reference point sounds counter-intuitive, it is technically in line with the method used by the World Meteorological Organisation (WMO).
The WMO's guidelines state that a 'reference station' - meant to monitor climate and detect changes at a national level - must have at least 30 years of rainfall and temperature data and be sited away from urban centres.
For the NEA, the Changi station is that reference station, and it said the rainfall trends there have reflected those at other stations across the island.
It said the Changi station has shown that more rain has fallen, but the increase has not been statistically significant.
But it conceded that half its weather stations across the island had logged higher, 'significant' increases in rainfall, including the stations in the central catchment area of MacRitchie and Paya Lebar; however, the stations near Orchard Road and Bukit Timah, which were hit by floods in recent years, had recorded no significant increases.
The agency is standing its ground on using the Changi station as its reference point, saying the method, and not using rainfall figures for the whole island as the panel did, fits WMO guidelines.
However, it said it would start putting on its website rainfall data from the various points across the island.
Climate scientists said the NEA should clarify what it considers a 'significant increase' in the amount of rainfall.
Assistant Professor Koh Tieh Yong at the Earth Observatory of Singapore said this would make clear if other groups such as the panel are evaluating the data using other standards.
Prof Koh recommended that the agency use at least some other stations that fit the WMO guidelines for reference stations to track rainfall trends across the island.
'If you want to know about rainfall over the island itself, then certainly you would welcome as much data as possible,' he said.
