SINGAPORE'S resident population will decline and become older if the birth rate remains extremely low and new immigrants are kept out.

This will remain the case even if Singapore produces more babies while stopping new immigrants from coming here.

These are some of the findings from a 2007 project released yesterday by the Institute of Policy Studies (IPS).

Spearheaded by lead researcher Yap Mui Teng, the project generated 48 scenarios showing how Singapore's resident population - comprising citizens and permanent residents - would change based on its total fertility rate (TFR) and migration levels.

The TFR refers to the average number of children that would be born to a woman over her lifetime. Four key scenarios help to illustrate the problems the country faces.

Firstly, if the TFR stays at 1.24, the figure recorded in 2005, and with zero net migration, Singapore's resident population would peak at 3.68 million in 2020, and decline to 3.03 million in 2050 (Scenario 1).

Even if the TFR is raised to 1.85 - from the current rate of 1.15 - the resident population will peak at 3.73 million in 2030 before falling to 3.37 million in 2050, as long as there is zero net migration (Scenario 4).

Population growth beyond 2005 is attributed to "population momentum", whereby the number of births exceeds the number of deaths - until a stage when fewer young people reach reproductive age and the number of deaths increases as the population ages.

However, if 30,000 net migrants are added annually, the total resident population may rise from 3.55 million in 2005 to about 4.89 million in 2050 - even if the TFR stays at 1.24 throughout this period (Scenario 2).

And, if 60,000 net migrants are added annually while TFR stays at 1.24, the resident population may grow further to 6.76 million in 2050 (Scenario 3).

Given such scenarios, "it is impossible not to have in-migration", said Dr Leong Chan Hoong, IPS migration studies researcher.

"What Singaporeans want to know is whether the people we take in are relevant and beneficial to the Singapore economy and justified."

The study also found that, with low fertility and no immigration, the number of youth aged up to 14 is likely to decline from 699,000 in 2005 to 274,400 by 2050.

Adding 30,000 net migrants annually throughout this period will help to relieve this decline, with the number of youth in 2050 projected to be about 650,000 - slightly lower than that in 2005.

In the scenario where 60,000 net migrants are added annually throughout the projection period, the population of resident youth will be 1.04 million in 2050.

If fertility is raised but the population is closed to migration, the population of resident youth may decline to about 440,000.

The study found not much difference in the number of seniors in all scenarios until after 2030. This is because, until then, the seniors of the future are already born and exist in the population, and the results of in-migration will be felt only later.

Dr Leong said: "Most people are not saying that we should have zero net migration. It is essentially about how much we can absorb, based on psychological comfort, infrastructure and capacity."

Based on the research findings, he said: "As long as new immigrants do not infringe on the values of Singaporeans, most Singaporeans are fine."

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